Wild Side: Shoreline bugs

Though they sometimes turn up in places far from water, they call them “shore bugs” for a reason.

Pentacora sphacelata, a shoreline bug that is common on the East Coast. —Matt Pelikan

I’ve been thinking a lot about shorelines lately, and the complex mix of challenges and opportunities that the meeting of land and water poses for wildlife. An oceanic shoreline, especially, with its high salinity, constantly changing water levels, and periodic disruption by storm-driven surges and waves, is a fascinating thing to explore. What creatures live there, and how are they adapted to the volatile and often hostile conditions?

A shoulder injury has restricted my paddling activity over the last two years. But when I can do it, a canoe or kayak is a favorite way to explore the Island’s cove heads, creeks, marshes, and barrier beaches. A shallow-draft boat and a little arm power can take you to discoveries you could never make any other way.

On a warm day in early July 2019, I took advantage of high tide to take my kayak up into the channels that cut the saltmarsh adjacent to Felix Neck. If you time it right, you can ride the rising tide up into the marsh, explore with the water at its deepest, and then drift effortlessly out as the tide turns and the channels begin to drain.

My records for the day highlight swarms of flies, skittering over mats of algae. The photos I managed were not great — it isn’t easy to photograph tiny, active insects while also holding a small boat steady in a tidal current — but I think these were long-legged flies (family Dolichopodidae) in the genus Hydrophorus, which appears to be quite common in wet, especially brackish habitat on Martha’s Vineyard. I doubt I’ll get any farther: this is a big genus, with more than 50 North American species, and mediocre photos are unlikely to show the right details for a precise ID.

But that expedition also produced my first-ever observations of a much less frequently reported group: the shore bugs, in the family Saldidae. These are bugs in the precise sense — that is, members of the order Hemiptera — and while they are said to sometimes turn up far from water, they’re called “shore bugs” for good reason. Most species stick closely to shorelines, with different species showing preferences for different settings.

An aquatic insect expert recently helped me ID the shore bugs I photographed that day: Pentacora sphacelata, a widely distributed insect that is said to be common. It occurs along most of the East Coast and the Gulf of Mexico shoreline, in the Caribbean, and down to Central and South America; there are at least a few records from the Mediterranean, which, as far as I can tell, reflect introduced populations in a region where this species is not native.

One thing I can tell you about Pentacora is that it’s monumentally twitchy! They were easy enough to spot as they basked or foraged on mud or algal mats. But attempts to drift close enough to take photos invariably sent the bugs darting into concealment before I got within range. I found them much harder to photograph than the flies, which were themselves mighty wary insects.

But if actively stalking your subject doesn’t work, you can always try lurking in ambush. I found an area that had a lot of bugs. Lifting one leg out of the kayak and burying that foot in the muck at the bottom of the channel, I held the boat as close as I could to where I had seen the insects and twisted my body so I could point the camera roughly where the critters had last been active.

After a while (probably just a few minutes, though given my contorted position, it felt like hours), the bugs began re-emerging. I was able to watch them darting across the algae in search of food; I even saw a pair mating. With my camera pre-aimed, I managed a handful of decent photos (and a large number of indecent ones).

Aside from its uncooperative nature, very little seems to be known about P. sphacelata. Like most Hemiptera, they possess tubular mouth parts — essentially extendable straws — for piercing and sucking. While many Hemipterans apply that tool to plants, shore bugs are said to be largely predatory. (I didn’t see any take prey). As you’d expect, Pentacora, like other shore bugs, is highly adapted to life on the water’s edge, handling brief immersion with aplomb and undeterred by the high salt levels in its habitat.

Since that day, I’ve only encountered shore bugs one other time, on a gravelly section of shoreline along the Edgartown Great Pond. The very different setting suggests that this might be a different species from the one I found in the salt marsh. But the photos I managed on that occasion were simply too bad to do much with.

So there remains a lot of mystery around these insects on the Vineyard. How many species do we have? What types of shorelines do they live on? I’m already scheming up ways for a guy with only one functional shoulder to answer these questions in the coming year!