Wild Side

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Luna moth. — Photo by Danielle Zerbonne

The great outdoors can produce baffling mysteries. MVTimes Wild Side columnist Matt Pelikan tries his best to solve them. Got a question for the Wild Side? Send it to onisland@mvtimes.com

Here’s a good one –  a picture of a luna who battled his way inside my house and thrashed around until he finally settled on a jar of capers in my pantry. He was attracted to our porch light. Why is that? At one point I used to leave the porch light on overnight so I could go out in the morning and see what had gathered. But then I felt guilty watching the chickadees pick them off one by one from the screen in the morning.

The Pelikan brief:

You think a porch light is attractive to moths? Try putting out an ultraviolet “black light” sometime! Many kinds of moths just can’t resist black light; in fact, biologists studying moths routinely use ultraviolet light sources to attract moths for collection or observation. But while the tendency of moths to fly toward light, and toward ultraviolet light in particular, is well known, nobody has come up with a fully satisfactory explanation.

The rest of the answer:

Most likely several factors play a role, and it’s also probably that different moth species respond to light for different reasons. And it’s worth keeping in mind that, for most of the evolutionary history of moths, all or most of the light at night came from the moon, stars, or the sky glow before sunrise and after sunset. So today’s situation, with artificial light sources popping up everywhere in moth habitat, is not what moths evolved to experience.

Moths are simple animals, and their needs in life boil to the usual basics. They need food, they need a mate, and it’s helpful to have some way of finding their way around. Explanations have been offered that relate to all three of these needs. For example, many adult moths feed on nectar from flowers. And many flowers glow under the ultraviolet lightt that makes up part of incoming sunlight (it’s the flower’s way of advertising for pollinators to come visit). So there may be some primitive tendency in moths to fly toward ultraviolet light in expectation of a meal. This tendency, then, would bring moths in to human light sources, at least ones that emit part of their energy in the ultraviolet range.

Many kinds of moths may also patrol large areas to find mates, and in order to be efficient about it, would want to avoid going over the same area repeatedly. One way to do this is simply to fly in a straight line, and some moths may use the moon or bright starts to help this. If you head toward the moon, or keep it on, say, your starboard beam, you’ll keep moving in a roughly straight direction. But if you try this with a light source that is much closer than the moon, you either arrive there and then don’t know what to do next, or you end up circling the light in an effort to keep it at the same angle. Both mechanisms could bring moths to light.

Finally — and I get in over my head on this one — some biologists noted a similarity between the frequency of ultraviolet light and the resonant frequency of some of the chemicals, called pheromones, that moths produce to lure potential mates. In other words, ultraviolet light somehow remind moths of the irresistible smell of a mate, even though one stimulus is a visual one and the other is a scent.

So take your pick: any, or all, or none of the above. Many kinds of moths are attracted to light, and that’s really all anybody knows for sure. But there is also agreement that in today’s environment, moths are paying a price for their fondness for light. The moths around your porch light are essentially wasting their time, hanging around in a sterile habitat that is unsuitable for them to live or reproduce in. Disruption of moth life cycles by artificial lighting is a real problem, and it’s one you can help with by turning outside lights off unless you are actively using them.

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On the Vineyard, bog copper butterflies are only found in sphagnum bogs with thriving wild cranberry, and they rarely venture far from their specific bog. — Photo by Matt Pelikan

“The fox has many tricks,” goes the saying. “The hedgehog has only one — but it’s a good one.” And so it is in nature: some species thrive by being flexible, while others evolve to be perfectly adapted to a very specific niche.

Consider, for example, the bog copper butterfly. Of all the Vineyard butterflies, this is the one most closely tied to a particular setting: sphagnum bogs rich in wild cranberry. You won’t find this tiny, delicate insect on the Vineyard outside a bog, and its life cycle is intimately tied to both that habitat and the wild cranberry that is the only plant the butterfly’s caterpillars will eat.

The bog copper, with a geographical range encompassing the northeastern United States and much of eastern Canada, is a close relative of the American copper, a versatile butterfly which you likely have in your yard. But somewhere along the evolutionary road, the bog copper opted for hyper-specialization, a life cycle centered on the challenging but predictable conditions of a bog.

Perhaps the biggest challenge a bog-dwelling insect faces comes from changing water levels. With limited mobility or none at all, the eggs and caterpillars of the bog copper need to be able to survive by exposure to air and prolonged submersion. Indeed, bog coppers are so well adapted to a wet environment that drying out is the real risk they face. A detailed study by entomologist David Wright, published in 1983, describes the fascinating adaptations of this butterfly.

cranberry-blossom.JPG
The cranberry blossom.

Female bog coppers lay their eggs in late spring, one at a time, near the base of wild cranberry plants. In dry times, dew or any rain that falls beads up on the cranberry’s waxy leaves and is funneled down the stem to wet the butterfly eggs. And when water levels rise with fall or spring rains, the egg turns out to have a layer of air under its outer skin, allowing the egg to develop even under water.

The caterpillar begins its development inside the protective envelope of the egg, and then goes nearly dormant through the summer, fall, and winter, hidden from predators and buffered by the egg from changes in moisture. Come early spring, the caterpillar leaves its egg, begins feeding on cranberry leaves, and starts to mature. Again, it’s adapted to submersion: a tight layer of hairs on its body traps a layer of air that allows the exchange of gasses (specifically dissolved oxygen) from the water to the caterpillar’s tissues.

When mature, the caterpillar briefly pupates to change into an adult. Even here, the butterfly has a special talent: the pupa is equipped with a rasp-like structure that can make noise when the pupa twitches. It’s a tenuous last line of defense, but the noise might deter ants or other predators that attack the pupa.

Emergence of the mature butterflies is closely timed to the flowering period of the wild cranberry, tracking that bloom period through its year-to-year variation. The adult butterflies take nectar mainly from cranberry blossoms, and are likely an important pollinator of the cranberry plant. From time to time, adult bog coppers engage in brief, swirling mating flights or territorial disputes. But mostly, they sit — on cranberry plants, naturally — waiting for a member of the opposite sex to pass by.

Bog coppers are weak flyers with little inclination to leave their bog and their cranberry plants. I’ve never found this species outside a bog, and unless two bogs are very close together, there is little or no intermingling of the bog coppers that reside there. Ordinarily, you’d expect that inbreeding would weaken the gene pool of each of these little populations, resulting in its eventual extinction. But this butterfly is so well adapted that inbreeding actually strengthens its survival: the unique adaptations for survival in a particular bog are reliably passed down to the next generation, with little variation.

Bogs suitable for this butterfly are not numerous on the Vineyard. Small bogs can’t support enough butterflies for the population to persist for very long — though they may serve as “stepping stones,” helping the odd individual make it from one large bog to another nearby, if there is one. And commercially worked bogs usually don’t support the butterfly because of insecticide use or simply the physical disturbance of working the bog — a form of disruption evolution didn’t anticipate. But of the large and cranberry-rich bogs that we do have, a high percentage seem to support bog coppers. In some cases, the butterfly populations in those bogs may have been isolated from immigration for decades, even centuries.

The risk the bog copper takes, of course, is that conditions in its bogs will change, or that bogs will be destroyed. If the population in a bog winks out, recolonization of that bog depends on the rare arrival of a wanderer from another bog. And if no suitable bog is nearby, recolonization approaches impossibility. For now, several large bogs and bog complexes on the Vineyard support good numbers of this unique butterfly. But the bog copper’s survival here depends on keeping those bogs in a healthy, natural condition.

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If your oak tree is sporting bright green orbs, read on. — Photo by Danielle Zerbonne

The great outdoors can produce baffling mysteries. MVTimes Wild Side columnist Matt Pelikan tries his best to solve them. Got a question for the Wild Side? Send it to onisland@mvtimes.com

What’s this…thing growing on young oaks in the woods behind my house?

The Pelikan Brief:

Galls — actually pretty interesting — occur when an insect (generally a wasp) hijacks the tissues of a plant to produce a little wasp nursery. In effect, the wasp induces a tumor and then the wasp larvae mature inside the “tumor.”

The rest of the answer:

Galls are a catch-all term for abnormal growths on plants that are induced by insects. Generally, galls serve as nurseries in which insect larvae can mature. The structure of the gall protects the larva or larvae while it grows, and the maturing insect draws its nourishment from the tissues of the plant. To put it bluntly, galls are tumors that insects deliberately cause in plants to meet their own needs.

While they can be dramatic and (depending on your perspective) unattractive, galls rarely do any serious harm to the plant they’re on. The insect that forms the gall, clearly, has an interest in keeping the affected plant healthy, because the plant is nurturing the insect’s offspring. One exception to the “do no harm” rule, though, has been very much on the radar of Vineyard horticulturalists: a wasp named Bassettia ceropteroides apparently colonized the Island recently, and the lumpy little galls it forms on oak twigs block the flow of fluids through the oak’s transport system. The leaves and growing tips of the oak die, and without the ability to produce leaves, entire oaks die as well if they are heavily infested. In my Oak Bluffs neighborhood, several oaks about three feet in diameter, which must be hundreds of years old, succumbed after just two years of infestation by this tiny pest.

Beyond the basic commonalities of gall formation, this is an incredibly complex phenomenon. Many thousands of insect species are capable of forming galls; in most cases, each type of insect requires a specific plant species in order to form galls successfully. Often the plant needs to be at a specific stage of growth in order for a gall to form. Galls can form on roots, leaves, or stems. What triggers a gall to form varies depending on the insect: chemicals in adult insects, eggs, larval insects, or insect secretions or saliva can all be the active agent in triggering gall formation.

Gall formation is an especially common strategy among a wasp family called Cynipidae, which has many hundreds of species in North America alone (the villainous Bassettia ceropteroides is a Cynipid). You might say that this family evolved with gall-formation as its central reproductive strategy. But thousands of insect species across six different insect orders — from mites to moths — have been shown to make galls. Gall formation is a common ability in insects, and the ability to do it must have arisen multiple times during the course of insect evolution.

Which is pretty remarkable when you think about it: to form a gall, an insect species must develop the ability to hijack the biochemical processes that govern tissue production in a plant, producing a structure that perfectly suits the insect’s needs. Galls are a great example of the highly specialized interactions that govern the lives of many types of insects.

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This is a volatile butterfly, playing by its own rules, and I just can’t figure it out. The natural world never stands still, and most of the time, once you’ve answered a question about a wild species, it’s time to start answering it again.

The Juniper Hairstreak butterfly. — Photo by Matt Pelikan

I don’t know whether it’s a source of frustration or of ever-expanding interest. But the natural world never stands still, and most of the time, once you’ve answered a question about a wild species, it’s time to start answering it again. Your knowledge is always, always obsolete.

This principle is much on my mind right now as it applies to one of my favorite butterflies, the juniper hairstreak. Fifteen years ago, I felt I had a good read on this distinctive insect on the Vineyard: it was rapidly expanding from a beach-head in Oak Bluffs and Edgartown, and would soon occupy suitable habitat across the Island. But the expansion of the species on the Vineyard seems to have stalled, and I can’t quite tell if its numbers are plummeting, or if I’m not looking for it enough, or in the wrong places.

If you look where it occurs, the juniper hairstreak is fairly easy to find, and very much worth the effort. Like other hairstreaks, it’s a small butterfly, about the size of a dime when it perches with its wings folded over its back. Also, like other hairstreaks, its underside bears an elaborate pattern of stripes. But this species is distinctive because the basic ground color of its wings is olive — it is the Island’s only predominantly green butterfly, and fresh ones, especially, are stunningly beautiful.

The juniper hairstreak associates very closely with red cedar, though it uses relatives of this plant elsewhere across the butterfly’s continent-spanning range. Males spend most of their day perched on the tip of a twig, usually in the upper branches of a cedar. Females lay their eggs — tiny, ridged, pale green spheres — on twig tips as well, and the larvae, or caterpillars, spend their entire period of development eating cedar leaves. The species goes through two full generations each year on the Vineyard, with adults from the first one, which overwintered as pupae, active mostly in late April and May and adults from the second one flying in late July and early August.

Sometimes you can spot the profile of a juniper hairstreak perched on a twig-tip. During the appropriate season, I habitually scan cedar trees with my binoculars, looking for exactly this. But the best way to find this butterfly is to grab the highest branches you can reach on cedar trees and give a few hearty tugs. The main thing that happens is that a shower of prickly cedar leaves rains down on you, with much of the debris making its way scratchily down inside your shirt. But if you happen to be tugging on a cedar with hairstreaks on it, you’ll see them jolted into brief, swirling flight. Track them, wait for them to land, and enjoy binocular views of, arguably, our prettiest insect.

The juniper hairstreak’s history here is easy to recite since it’s quite short. Though looked for, this butterfly was unknown on the Vineyard until the mid-1990s, when a visiting naturalist named Paul Miliotis found some in a large stand of cedars on East Beach, Chappaquiddick. That alone was a bit of a puzzle: how long had they been there, and if they were recently arrived, why on earth did they arrive there instead of East or West Chop, both of which have plenty of cedars and both of which are closer to the mainland?

By 1998, my first spring on the Island, juniper hairstreaks proved to be all over Oak Bluffs; on some occasions, I found as many as 25 at a single location. I began shaking cedars elsewhere on the Vineyard, eventually finding this species as far south as Katama and as far west as West Tisbury. The pattern was one of expansion: where they were absent one year, they were present the next. But somewhere along the line, this pattern seems to have reversed. The cedars remain common, but it has been years since I’ve found the species outside of Oak Bluffs. Even there, it seems to be scarce at locations that formerly supported it in large numbers.

I found a juniper hairstreak this past weekend, probably an adult from the first generation, running late because of our protracted winter. I’ll check the area where I found it later in the season, hoping to find a solid population. But I’m wondering: was the abundance of this species circa 2000 a temporary thing? If so, how many times has the species expanded and contracted — possibly even disappeared and reappeared — on Martha’s Vineyard, and what prompts that pattern? How much of its current scarcity reflects a real decline in numbers, and how much reflects a shift of the population from places where I can find it to places where I can’t? This is a volatile butterfly, playing by its own rules, and I just can’t figure it out.

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With a long tail and short, rounded wings, male Cooper’s hawks are smaller than crows.

Juvenile Coopers Hawk — Calibas, Wikimedia Comm

Last weekend, while looking for butterflies along a fire lane in the State Forest, I was surprised by a sudden halt in the bird songs that were providing the soundtrack for my stroll. A prairie warbler, which had been reciting its ascending buzz with the regularity of a clock, missed his cue; a chipping sparrow bit off his song in mid-trill.

This sort of thing makes birders look up. So I did. And as is supposed to happen at such moments, I found myself trading stares with a smallish hawk passing almost over my head. A long tail, and short, rounded wings marked this as a Cooper’s hawk; its modest size, clearly smaller than a crow, marked it as a male. Gripped in its feet, pulled snuggly against its belly like a football in a fullback’s hands, the hawk carried a small, gray item – probably a meadow vole, hardy unprecedented but not quite a typical prey item for a Cooper’s, since this woodland hawk specializes in catching birds.

The hawk, making good time on firm, steady wingbeats and clearly aiming for a nearby stand of evergreens, did not appear happy to see me. It instantly veered off course and rapidly climbed. In a few seconds, it was in full soar, wings out straight and tail fully fanned, perhaps 200 feet above me. It circled a couple times, then banked steeply and dove toward a point on the other side of the evergreens it had originally been flying to. I lost sight of it, and in a few minutes, the birds were singing again.

It was not hard to figure out what was going on, and indeed, this kind of thing happens quite often these days. A hawk making a bee-line with prey in its talons in early June is on its way back to a nest, on the way home from doing some shopping for its mate and offspring. The sudden change of direction by the hawk I observed was aimed at concealing the location of the nest. The steep climb and circling simply reflected the bird taking a good look around, making sure I was alone and that no other threats were in the area. And the sudden plunge was probably the start of a more discreet approach to the nest, through the back door. I was probably standing within 100 yards of so of an active Cooper’s hawk nest.

The relationship between humans and Cooper’s hawks has not been a happy one. The hawks, being optimized for bird-hunting, have a hard time passing up chickens. And farmers, not wanting to lose chickens, for many years responded by shooting the hawks. Sport gunning for these “undesirable” birds of prey also took a heavy toll. While never really close to extinction, in the early 20th century the Cooper’s hawk was largely erased as a breeding bird in well-settled areas in our region.

Legal protection, a regional decline in farming, and a better appreciation of wildlife has resulted in fewer Cooper’s hawks being shot, and the species has steadily rebounded in numbers over the past few decades. Long a staple of the fall hawk migration on the Vineyard, Cooper’s hawks began (or, more precisely, resumed) breeding on the Vineyard about 20 years ago. It’s hard to tell how many pairs nest here, because these birds travel widely in search of prey, and they do their best to be discreet when they have eggs or young. But based on how often and how widely I see this species during the breeding season, I’d put our current nesting population somewhere around 20 pairs, and I’m convinced the number is growing slowly but steadily.

While known to nest in a wide range of settings, Cooper’s hawks are said to have a special fondness for nesting in white pines, and on the Vineyard at least, I think they almost always nest in evergreens of some kind. Concealment is surely the reason. While adult Cooper’s hawks have little to fear from other predators, the relationship between crows and Cooper’s hawks is one of mutual detestation. Crows simply can’t see one of these hawks without harassing it; they’d eat the hawk’s eggs or nestlings if they got the chance, and by mobbing adult hawks whenever they see one, crows spoil the hunting and delay the return of adult hawks to the nest.

Cooper’s hawks remain a common fall migrant on the Vineyard, their numbers peaking in early October, with some birds lingering on the Island through most winters. The species is much less obvious, and probably less numerous, during spring migration. One puzzle is whether our nesting population migrates south, or, as with our red-tailed hawks, reflects a distinctive, sedentary population of a generally migratory bird.

In any case, the Cooper’s hawk appears well established as a breeding bird here, and the eerie silence as songbirds catch sight of an approaching Cooper’s hawk will be a common event for alert Vineyard naturalists for years to come. Don’t forget to look up.

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Duskywings look like moths, but they are in fact butterflies. — Photo by Matt Pelikan

I’ve always had a fondness for groups of organisms that are closely related and similar to each other. There’s a certain elegance in the way nature improvises on the theme of a good idea, with a common ancestor rapidly (by evolutionary standards) diversifying into a cluster of species, resembling each other but each occupying its own niche.

The duskywings are hard to tell apart, but "hyaline" spots – like little translucent windows on their wings – distinguish one species from another.
The duskywings are hard to tell apart, but “hyaline” spots – like little translucent windows on their wings – distinguish one species from another.

The duskywings are a perfect example. These are butterflies in a particular genus, Erynnis, five species of which inhabit the Vineyard. Drab and only about an inch in wingspan, they don’t really fit the popular notion of a butterfly, and the untrained observer, encountering two different species of duskywings, might not even notice a difference. But butterflies they are, and to my mind they present a fascinating mix of similarities and individuality.

As is the way with butterflies, our duskywings differ in what type of plant their caterpillars feed on. Three of our species feed on oaks of various kinds; a fourth feeds on aspen; and the fifth, on a common wildflower of dry, sandy areas called wild indigo. Oaks, of course, are nearly inescapable on the Island, and it’s easy to find places where wild indigo overlaps with oak. There are even a few spots — the northwestern corner of Correllus State Forest is one — where these plants occur along with aspen, meaning that all five duskywings can occur in the same spot. I’ve found all of our duskywings along the fire lane that heads east from County Road along the northern edge of the State Forest.

As is also the case with related butterflies, the duskywings differ at least a little in the timing of when their adults are on the wing. But right about now, sometime during the second half of May, the flight periods of all five species overlap. So, in theory anyway, you could find all five in the same place at the same time! The most I’ve managed in a day is four species, but trying for a clean sweep is one of those pointless but amusing exercises that makes insect-hunting so much fun.

The similarity of duskywings makes identifying these butterflies a challenge, though it’s a challenge that eases rapidly once you learn a few tricks. Rapid, bouncing flight and a strong territorial tendency are behavioral traits that help one spot duskywings in general. But beyond that, these are basically dark brown insects with mottled patterns that are difficult to describe or remember.

Happily, one unambiguous trait divides our duskywings into two groups: the presence of so-called hyaline spots — little translucent windows in the wing — distinguishes three of our species, while the other two lack these details. And of the three with hyaline spots, two species feature large spots while on the third, the spots are tiny. So these spots are a critical aid for identification. Duskywings often perch, helpfully, with their wings spread wide, making it easy to look for hyaline spots.

Named after Roman poets, Juvenal’s and Horace’s duskywings are the ones with the big hyaline spots. Juvenal’s is invariably the first duskywing to fly each spring, usually by the third week of April, and is among our most common butterflies. Horace’s is rare and, unlike Juvenal’s has flight periods in both spring and summer (so a “big-spotted” duskywing in late July is surely a Horace’s). Otherwise, these two are hard to tell apart: a pair of pale spots on the underside, present on Juvenal’s but absent on Horace’s, is the most helpful field mark.

The “small-spotted” species, wild indigo duskywing, also has spring and summer flights but is fairly easy to identify because its distinctive hyaline markings. Also, this butterfly is rarely found more than a few feet from its host plant, so location offers a useful cue.

Of the “spotless” duskywings, the sleepy duskywing, an oak-feeding species, is by far the more common, usually on the wing in respectable numbers from late April through the end of May. It is a small and dark species, and after years of watching duskywings, I can often pick this species out even in flight by these characteristics.

Even smaller is the final duskywing, dreamy, which has the aspen-feeding caterpillars. Flying in late May and early June, it features extensive grayish frosting on the outer part of its wings. It’s the prettiest duskywing (which isn’t saying much), but sadly it’s also the least common on the Vineyard; I’ve only encountered it here a handful of times and have only managed one decent photograph of it, years ago in my pre-digital, slide-shooting days.

In the grand scheme of things, these are not particularly important insects. They’re neither helpful nor harmful from the human perspective, and their disappearance would likely have little ecological effect. But I value my acquaintance with them: knowing these insects, I feel like I have a secret perspective on the Vineyard landscape. And the season’s first Juvenal’s duskywing, bopping across a path or clearing, is always a welcome sign that spring is here to stay.

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The insect is probably Nomotettix cristatus, northern crested pygmy grasshopper, but the author does not know for sure, and may not be able to find out. — Matt Pelikan

Times have never been better for the amateur naturalist. Excellent field guides keep coming out, addressing harder and harder groups of organisms. Internet sources like Bugguide.net provide vast catalogs of indentified photos to compare a subject to. Digital photography has greatly simplified the process of capturing a good image of what you find. And a vast network of helpful experts is getting steadily easier to tap into.

But the study of natural history remains endlessly challenging. Sometimes you bang up against a genuine gap in knowledge — nobody may know, for example, how to tell the members of a fly genus apart without dissecting specimens. Other times, the knowledge is out there, but the subject is so obscure that you can’t find it. But most often, your own ignorance and wrong assumptions lead you astray. The study of nature has a built-in measure of frustration.

I’m wrangling with a good example of this, and the history of my relationship with the organism in question illustrates how the study of nature often goes (or doesn’t go). The story starts about a dozen years ago, when I first noticed some type of tiny hopping insect along the fire lanes of Manuel F. Correllus State Forest in early spring. Perhaps three-eighths of an inch long at most, these grayish mystery critters were perfectly camouflaged against the sand: I usually noticed them only when they jumped, and then my eyes simply couldn’t follow them. Unable to get a decent look, I had no idea what they might be.

Over time, after catching glimpses of dozens of these mystery insects, a vague impression of their appearance evolved. Stout and seemingly arched along the center line of their backs, they aligned most readily with my mental image of a leaf-hopper. So I perused photos of leaf-hoppers, hoping in vain for a match that might at least be close enough to point me to toward some subset of this vast family (it has more than 20,000 members worldwide).

Barking up this very wrong tree might have been the end of the story if one of these critters hadn’t landed, coincidentally, almost under my nose as I was photographing something else. Finally getting a decent look, and even a poor but possibly helpful photograph, I realized I was actually seeing a grasshopper, wholly unrelated to the leaf-hopper I had surmised. Grasshoppers I know at least a little about, so this seemed like progress!

But again, I bungled. Such a tiny grasshopper must be an immature nymph, right? And to be active early in mid-April, such a nymph would have to belong to a species that either overwinters as nymph, or hatches very early in the season, right? These seemingly reasonable assumptions had me searching for a match among photos of band-winged grasshoppers, a large grasshopper family that contains all the species I know of that are active in early spring on the Vineyard.

Meanwhile, I posted my bad photo on various websites and Facebook groups, seeking assistance putting a name to the beast. Shortly, I received a response that didn’t provide an identification, but at least revealed the flaws of my thinking: the insect wasn’t a nymph at all, but rather an adult member of a group called the pygmy grasshoppers. Aptly named, these tiny grasshoppers overwinter in their adult stage, a behavior I had never heard of among grasshoppers and therefore hadn’t even considered. And it had never occurred to me that there might be pygmy grasshoppers on the Vineyard.

With a gradually developing sense of what to look for and where to look for it, I finally managed to spot a few of these insects before they disappeared, and then, stealthily, I closed in for some better pictures of one in the moments before it bounded away, its powerful legs making an audible “snap” as it took off. The photos revealed an odd but distinctive design: as on most pygmy grasshoppers, the exoskeleton of the thorax extends backward to the insect’s tail end (the beast lacks visible wings). And along the center line of this extension of the thorax runs a raised and serrated ridge.

At present, I think these traits narrow this insect down to the genus Nomotettix. It’s probably the species cristatus, sometimes known as the northern crested pygmy grasshopper. I’ve sent my photos out to a couple of experts hoping to either confirm this, or else correct my latest error! But I’m prepared to learn that my photos aren’t sufficient to tell what species it is. In any case, the experience has been a useful reminder of how much patience matters to a naturalist, as you navigate a winding path through incomplete knowledge and false assumptions.

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There are scores of bee-fly species on the Vineyard alone, but like so many groups of insects, our bee-flies have never been seriously studied.

Bombylius major belongs to a family known familiarly as the “bee-flies,” due to their uncanny resemblance to bees. — Photo by Matt Pelikan

If you run into Bombylius major — and it’s easy to do, since this species is common on Martha’s Vineyard — you might find yourself puzzling over what, exactly, you’re looking at. About a half-inch long, plump and fuzzy with an almost spherical abdomen, Bombylius sure looks like a bee. But a closer look, if you manage one, tells a different story: this species has stubby antennae and only one pair of wings, physical traits that land Bombylius squarely in the fly department.

It’s not too surprising, then, that Bombylius major belongs to a family known familiarly as the “bee-flies,” due to their uncanny resemblance to bees. (The genus name “Bombylius” echoes “Bombus,” the genus to which our true bumble-bees belong). Bee-flies are a diverse and hugely successful division within the flies, with many thousands of species known (just the single genus Bombylius has more than 250 members). There are surely scores, and maybe hundreds, of bee-fly species on the Vineyard alone, but like so many groups of insects, our bee-flies have never been seriously studied.

Known commonly as the big bee-fly or greater bee-fly (despite the fact that its of middling size for this family), Bombylius major occurs naturally across much of the world. In addition to the traits I’ve already mentioned, this insect sports distinctly two-toned wings, with a dark leading half sharply distinguished from a transparent trailing half. The legs of Bombylius are long and delicate, and protruding from the front end is a fearsome-looking spike that might suggest a blood-sucking habit.

But don’t be alarmed: adult greater bee-flies are not the least bit aggressive, and they limit their diet to pollen and nectar taken from flowers. Given their early spring flight season on the Vineyard, these foods are often taken from blueberry and mayflower blossoms (about all that’s in bloom when Bombylius is at its peak of activity). The long proboscis, effectively just a straw, allows this fly to drink nectar from the deep, bell-like flowers of these plants.

If adults are benign, the larvae of the greater bee-fly are tough customers. Like most members of its large family, Bombylius is a parasite of ground-nesting bees. Female flies lay their eggs near or even in the burrow of a ground-nesting bee. I’ve never seen this behavior, but some accounts suggest that the eggs are flicked toward the bee burrow while the fly is airborne, aiming for the burrow like pilots releasing aerial bombs. The bee-like appearance of Bombylius may help it approach bee burrows without alarming the bees, and of course it may also deter would-be predators from attacking the fly.

Upon hatching, the fly larva bides its time while the bee industriously lays her own egg and provisions the burrow with pollen for the young bee to eat. As the larval bee nears maturity, the fly larva attaches to it, gradually devouring it as an external parasite. The maturing fly then overwinters in the bee burrow, tunneling its way to the surface in the spring before emerging as a fuzzy adult, ready to repeat the cycle.

Pollination is a beneficial role played by insects, of course, and it would be easy to frown on Bombylius because it preys on bees. But the greater bee-fly is itself a pretty fair pollinator, with its hairy body carrying pollen effectively from one flower to another. And there is presumably competition among bee species for pollen and suitable nest sites; bee parasites like Bombylius help keep bee populations in balance, ensuring that no single bee species grows so common that it squeezes out its relatives.

Greater bee-flies occur quite widely around the Island. But given their close association with ground-nesting bees, these flies are most common in areas with the dry, sandy soils that bees find most congenial for burrow construction. Fire lanes in Correllus State Forest are the easiest place to find Bombylius, and on a warm, sunny day in late April, I encounter one of these excellent flies every few yards.

Their small size and unobtrusive coloration make them a bit hard to spot, as does their active flight pattern: hover, dart, hover, nearly always within a foot or so of the ground. From time to time, you’ll spot a bee-fly visiting a flower, perching delicately on the flower’s rim and sometimes even continuing to beat its bicolored wings while that long proboscis probes the flower like a hypodermic needle.

Equipped, like other flies, with compound eyes that wrap around a good portion of the head, the greater bee-fly has remarkable vision and is very wary of moving objects (like people). When disturbed, they don’t usually move very far, but it is next to impossible to sneak up on one, and a pair of binoculars is almost essential if you hope to get a good look at this species. It took some crawling, but a high point of this past weekend was finally getting within camera range of one of my favorite flies!

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While there are plenty of dull-looking examples, beetles as a group include a lot of striking insects.

Even with frosty nights still lingering, ground beetles like this gnarly black Meloe are out and about, doing their thing. — Photo by Matt Peilkan

The earliest days that feel like spring rather than late winter are among my favorite days of the year — after the last of the snow has melted, and plants are just starting to break out of dormancy. It’s a time when the world still looks dead and it’s hard to imagine any insects stirring, until you look more closely and see that, in fact, a surprising variety of hardy bugs are on the move.

Following a crummy winter, it was not until this past weekend that it felt like spring had taken charge on the Vineyard. Sunday was not quite as warm as the bright sun suggested — our thermometer read 42 around noon. But the ground was thawing, and I inevitably ended up in Correllus State Forest, where sun-warmed soil along the fire lanes yields interesting early-season arthropods, as early as mid-March in some years.

It takes a certain amount of audacity for a cold-blooded insect to be out and about at this point in the season. A week ago, there was snow on the ground, and temperature at night still drops regularly below freezing. But the sun, shining stronger and longer with every day, can easily heat an insect up to operating temperature. For the relatively few insects that have mastered the problem of freezing while they’re in an active state, early spring is perfectly workable.

While there are plenty of dull-looking examples, beetles as a group include a lot of striking insects. An excellent example would be the so-called “oil beetle” I ran into on Sunday. More formally it’s a species (I can’t tell which one) in the genus Meloe. The six or eight species that seem possible on the Vineyard differ only in very subtle ways, but the odd qualities they share go well beyond the bloated, almost wingless, glossy black form these inch-long beetles take as adults. I find what I assume is the same species more springs than not on the same stretch of fire lane, and it makes me happy that I know a place where I can reliably find such a creature.

The name “oil beetle” (or “blister beetle,” a more general name for the entire family) derives from a bizarre defensive trait these insects have evolved. By and large, they’re sluggish insects, and you can tell by its looks that they are flightless and about as agile as a washing machine. But don’t mess with them. When disturbed, they’re said to exude a caustic chemical from their joints, a juice gnarly enough to raise blisters. This is not something I’ve felt it necessary to confirm by personal experience!

The life cycle of Meloe is bizarre as well, at least to human sensibilities, though it’s actually pretty tame by insect standards. Like most blister beetles, the members of this genus are known to be parasites of ground-nesting, solitary bees. Living as individuals rather than in colonies, such bees lay their eggs in burrows they’ve provisioned with pollen or other food for their offspring to eat while developing. In effect, a bee nest is a little cache of resources, and blister beetles, like a surprising number of other insects, have found a way to purloin it.

Blister beetles exploit the frugal provisioning habits of the bee by laying their eggs on flowers that the bees are likely to shop at. The larval beetle — which are even homelier than the adults if that’s possible — simply latch onto a bee’s body hair and hitch a ride to a burrow that’s being provisioned. There, the beetle grub lives on whatever the adult bee provides, and occasionally on the eggs or larvae she has produced.

At least some blister beetles reportedly locate areas rich in the appropriate kind of bee, whether by detecting the bees themselves or perhaps just by having an instinctive love of the same habitat the bees prefer. And while the associations of parasites and hosts is a vast subject that we know very little about, at least some blister beetle species are known to successfully parasitize only very specific bee species. Again, such tight and obligatory relationships aren’t unusual in the insect world.

Oddly, a second blister beetle species was on the move on Sunday, one that I had never encountered before. Tricrania sanguinipennis (it seems to have no common name) is smaller and has a more conventional shape than its cousin Meloe, with a prettier orange-and-black color scheme. But it shares much of the same biology. The females of both these species will mate and lay eggs in carefully selected sites as the spring progresses. The resulting larvae will waylay the requisite bees and, after maturing underground during the course of the summer, overwinter until the earliest spring days next year.

When I’ll be looking for them.

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Unimpeded in its upper reaches, Mill Brook winds its way through the Land Bank's Waskosim's Rock preserve. — Photo by Matt Pelikan

Matt-PelikanMatt Pelikan has been writing the Wild Side column since 2008. He is a restoration ecologist for The Nature Conservancy, and he lives in Oak Bluffs.

Native brook trout cling to survival in the brook’s upper reaches where cold water temperatures prevail.

Aside from a few brilliant seasons catching frogs when I was about nine years old, I haven’t spent much time exploring freshwater habitats. So I was happy to have the opportunity to learn from an expert last weekend, when I attended a presentation by Steve Hurley, Southeast District Fisheries Manager for the Massachusetts Department of Fish and Game.

The presentation, Sunday afternoon at the West Tisbury Public Safety Building, was attended by about 60 interested Islanders. Mr. Hurley discussed the results of two important studies of the Mill Brook, the Vineyard’s most significant stream system, which winds from Chilmark through West Tisbury to empty into the Tisbury Great Pond at the head of Town Cove. The Mill Brook is currently a subject of much study and debate as the Town of West Tisbury contemplates the future of the Mill Pond, an artificial impoundment on this stream just northeast of the town center and adjacent to the Edgartown-West Tisbury Road.

Streams, like any other ecological system, feature astonishing complexity. But as a practical matter, a few simple principles often suffice to explain a great deal about a stream. Drawing on a recent survey of the Mill Brook’s fish and a season-long effort to track water temperature at multiple points in the stream, Mr. Hurley developed an elegantly simple explanation for the distribution of various fish species.

The Island’s streams have always struck me as a bit incongruous in the Vineyard landscape: cold, gravel-bottomed, and often flowing quickly down fairly steep gradients, they seem like bits of Vermont transplanted to the coast. I learned from Mr. Hurley that this impression isn’t so far off. Fed mainly by groundwater, Island streams tend to be cold, and they support some cold-water fish species that one would also find in a northern New England river. The most notable of these is the brook trout, essentially a northern or high-elevation species that approaches the southern and lower limit of its distribution in cold groundwater streams of coastal Massachusetts.

Unlike cold streams in Vermont, though, our streams flow to the sea rather than into lakes or larger river systems. Some brook trout populations have developed a fascinating strategy to take advantage of this: during spring and summer, they descend their streams and enter saltwater, feeding in the rich waters of estuaries before returning to freshwater streams to spawn. In our coastal streams, in fact, such journeys are not unusual: many so-called “diadromous” fish split their time between freshwater and oceanic life. River herring, shad, smelt, salmon, and the American eel are among the diadromous species native to our region and requiring access from salt to fresh water.

Brook trout, wherever they are, require cold water, with about 70 degrees being the upper limit at which they can survive and temperatures below 60 needed for healthy growth. Historically, Mr. Hurley reports, sea-run or “salter” brook trout were abundant in the Mill Brook system. In the 2013 fish survey led by Mr. Hurley, a solid population of native brook trout – both adults and young fish – was documented in the upper reaches of the Mill Brook. But the species was virtually absent from the lower stretches of the stream, which were dominated by fish species that prefer warmer water, and there was no clear evidence of a sea-run brookie population.

An explanation for this pattern came from water temperature data from a survey supported by the Edey Foundation and the Sea-run Brook Trout Coalition. An array of data loggers placed at various points in the stream recorded water temperatures, and the results as presented by Mr. Hurley were startling. Predictably, upper reaches of the brook featured temperatures congenial to brookies. But at each artificial impoundment surveyed lower down in the stream, sun-warmed water from the pond crossed the spillway to heat the stream below. Above and below dams on the Mill Brook, sustained temperatures last summer reached well into the 80s, a level that produces brook trout chowder.

In addition to altering the temperature regime of the stream, Mr. Hurley pointed out, the half-dozen or so major dams on the Mill Brook form impassable physical barriers to brookies and other diadromous fish that might otherwise use the stream. Good numbers of eels were detected in the stream; but generally, the fish survey suggests, the Mill Brook functions poorly if at all as a resource for diadromous fish.

In considering whether to dredge the Mill Pond, remove the dam and restore the stream, or take some other course of action, West Tisbury will need to balance factors including ecology, recreation, scenery, and tradition. But Mr. Hurley’s presentation made it clear that, however natural one may think the Mill Brook is, in fact it’s a system that is vastly altered from its original state. Town leaders and residents should know that however familiar the stream’s artificial impoundments seem, they are recent developments in the overall history of the Mill Brook. And they are features that dramatically interfere with the life cycles of many fish that once flourished here, and could do so again.

For a complete report on the Sunday presentation, click here.