A “Shore Bug,” Pentacora sphacelata

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January 18, 2024 by Matt Pelikan

First Vineyard Record of Pentacora sphacelata

While kayaking in the channels cutting the salt marsh adjacent to Felix Neck in July 2019, I noticed a number of small, dark insects darting about on mud and algae exposed by the falling tide. Balancing precariously, using my paddle to anchor the boat while I held the camera with one extended arm, I managed to snap a few photographs.

It wasn’t until almost two years later, in June 2021, that I got around to reviewing the photos and uploading the few usable ones into iNaturalist. I was able to identify these insects only to the family level: Saldidae, or shore bugs, a small family of true bugs that are typically found in wet habitat at the water’s edge.

Fast forward another two and a half years, to January 18, when aquatic insect expert Matthew Pintar came across my photos and was able to provide a species-level identification: Pentacora sphacelata, a broadly distributed species strongly associated with salt marsh. It occurs all along the east coast of North America, with records also from California, South America, and the West Indies. It also occurs, apparently as in introduced species, at a few sites on the Mediterranean coastline.

This interesting bug is said to be common, and the worldwide database of the Global Biodiversity Information Facility (GBIF) contains 278 records (including two from Boston Harbor islands in Massachusetts). But as my own experience shows, getting a good look at one requires braving mosquitoes and salt marsh muck: relatively few amateur observers seem to have found this bug, and the one from Felix Neck represents the only Massachusetts observation in iNaturalist.

The episode is a great illustration of how effective iNaturalist can be at connecting amateur observers with scientific experts. It also piqued my curiosity about this specialized and relatively unknown family of bugs: how common is P. sphacelata on Vineyard marshes? Are there other members of this curious family present? How do these insects behave, and what do they eat? My only other observation of this family came from a very different habitat – a gravelly sand bar on the shore of the Edgartown Great Pond – and therefore might represent a second species of shore bug. But the poor cell phone photographs I managed in that instance don’t seem good enough to support of precise ID.

So Saldidae is now on my list for further investigation when warm weather returns! My guess is that at least a few other members of this family are present along Vineyard shorelines.

Matt Pelikan is the director of the Martha’s Vineyard Atlas of Life project at BiodiversityWorks. An enthusiastic paddler on the Vineyard’s ponds and bays, he keeps a camera handy at all times.