Wild Side: Bee happy

There are loads of bees on the Island, in every shape and size.

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With more than 200 species of bees having been documented on Martha’s Vineyard, it’s no surprise that our bee fauna exhibits a huge amount of variation. Large and small, social and solitary, specialist and generalist — we’ve got them all.

To take size as an example, our largest bees are impressive insects. Queens of a couple of our bumblebee species flirt with a full inch for their length; females of the Eastern carpenter bee, Xylocopa virginica, are larger still. And females of the nonnative giant resin bee, Megachile sculpturalis, established here though not yet common, can approach an inch and a quarter in length.

At the other extreme, a hefty majority of our bees are less than half an inch in length, and several fall well short of a quarter-inch. Yet these tiny bees do everything their larger relatives do: mate, build nests, gather pollen or other food supplies, and deal, in one way or another, with a host of potential predators and other threats.

Unless you’re seriously interested in insects and have some experience observing them, our smallest bees are below the size threshold for what you’re likely to notice. And it’s not just small size that makes them elusive: Most of these species spend most of their time down low, among vegetation, making them even harder to spot. But some of these bees can be quite common, at least locally, and they all exhibit complex and fascinating behavior.

So I was quite happy when West Tisbury naturalist Sharon Britton turned up a population of a tiny bee called Holcopasites calliopsidis at a conservation property in West Tisbury. Despite the impressive length of its name, Holcopasites is a tiny critter: Both sexes average around five millimeters long, and even that figure doesn’t do justice to the impression of smallness this species creates. A Holcopasites patrolling low over the ground, which is what they often do, is a tiny speck from the perspective of an upright, six-foot observer.

While it may actually be fairly common, this bee is a tough one to find, so I planned a visit to the site to see if I could repeat Sharon’s success. And I had a second tiny bee on my mind as I did so: Calliopsis andreniformis, a shade larger than Holcopasites and locked with that species in a very tight ecological embrace. Holcopasites is a kleptoparasite on Calliopsis, meaning that the former species, instead of making and provisioning its own nest, lays its eggs in the nests of Calliopsis. Larvae of the parasite grow to maturity on the food the host species stored for its own young, and sometimes by eating the larvae of the host species as well.

Accompanied by Molly Jacobson, a pollinator ecologist visiting from the College of Environmental Science and Forestry at the State University of New York in Syracuse, I wasted little time in visiting the site. Molly’s position, like my own at BiodiversityWorks, is funded by the Betsy and Jesse Fink Family Foundation, and the foundation arranges periodic visits by Molly so she can teach me and help with various projects I’m working on.

It was not hard to find our first Holcopasites, patrolling over hard-packed soil on a trail that runs along the edge of the preserve. Seen well, it’s a distinctive bee, stout in structure and sporting a white-spotted, reddish abdomen. Calliopsis took a bit longer to find, but we knew it had to be there: Why would a specialized kleptoparasite be common at a site that lacked its host species? Eventually we found one of the distinctive yellow-legged, yellow-faced males of Calliopsis andreniformis, and shortly after that, the plainer and slightly larger female. 

With patient observation, we realized that a modest colony of Calliopsis and its parasite stretched along about 100 feet of trail, giving us a superb opportunity to watch these two species interact. Male Calliopsis patrolled over the bare soil, searching for Calliopsis females to mate with. Holcopasites also patrolled, looking for Calliopsis nests to enter and lay eggs inside; a few Holcopasites also visited the yellow centers of daisy flowers to take nectar. And female Calliopsis were hard at work, some digging nest burrows, others entering completed nests with full pollen loads.

With so many of their nest parasites around, it was not surprising to find that female Calliopsis carefully concealed their nests at the bases of small clumps of grass or clover. This contrasts with other reports of the species nesting right in the open. Perhaps the presence of the parasite altered the behavior of female Calliopsis, or perhaps this population has existed long enough so that females with an instinct for nest concealment have come to dominate it.

Two hours and several hundred photographs later, Molly and I finally had to move on to another site. But spending such intimate time with two tiny, infrequently observed bees, and witnessing their interactions, left us feeling fortunate indeed.