An alert observer and the power of iNaturalist (iNaturalist.org) recently combined to add a regionally important insect record on Martha’s Vineyard! iNaturalist observer abgeorge found the animal, a large water bug known as Benacus griseus or Eastern Toe-Biter, on the beach below the overlook at the Gay Head Cliffs in Aquinnah on March 30. Taking excellent photos of the top and bottom of the insect, abgeorge uploaded the sighting via the iNaturalist mobile app and accepted a tentative identification, Lecotherus americanus or American Giant Water Bug, from the options proposed by the iNaturalist identification algorithm.
The ID was very plausible based on the appearance of the insect and the distribution of L. americanus, which is common in a broad swath across the middle of North America, according to the map of iNat records. The sighting caught the expert eye of iNat user mpinter, a post-doctoral specialist in aquatic insects at Florida International University with more than 66,000 (!) iNat identifications to his credit. Noting some fine details of anatomy that abgeorge‘s photos had captured, mpinter corrected the identification to the similar, closely related, but far more surprising species Benacus griseus.
Benacus griseus has a largely southern distribution, reaching southern New England but really centered in the deep South — Florida and the Gulf Coast. abgeorge‘s record is currently the northernmost East Coast one for Benacus in the iNaturalist database. The magisterial BugGuide.net database contains coastal-state records for B. griseus only as far north as Pennsylvania. It is not clear that Benacus actually lives on the Vineyard: the time of year and the recent pattern of strong southerly winds suggest that this individual may have been blown here from a more southerly location (yes, adult water bugs can fly). But abgeorge‘s attentive observation and photography resulted in a notable geographic data point for this insect. The record is included in the Martha’s Vineyard Atlas of Life project (run by BiodiversityWorks) on iNaturalist and can be viewed here: https://www.inaturalist.org/observations/72882056