Purple beach bug
April 17, 2010
I was on the beach yesterday and noticed a lot of these little critters flopping about. I was right near the water line, and I’m not sure if these were water critters that were getting beached or if they were beach critters that were getting swamped. They are small, about 2-3mm in length. As you can see, they have long appendages, but I couldn’t tell you for sure whether they are all legs or legs and antennae. Between the wind and the water, I couldn’t get one to stay still long enough to really see. Any ideas?
Windward/North shore, O’ahu, Hawaii
Many things in the world of insects and other arthropods resemble other creatures and mimicry is often used as a survival strategy. Our first impression, before lightening your image, was that this might be a Harvester missing a few legs, but we quickly ruled that out. The creature does appear to have six legs and antennae which is consistent with it being an insect. The front legs appear to be raptoral, a characteristic of many true bugs including predatory aquatic bugs. The behavior you describe was key to our hypothesis that this is some species of Water Strider in the infraorder Gerromorpha which is represented by several families on BugGuide. The inhabitants of family Gerridae are known as the Water Striders, and according to BugGuide the habitat is the “surface of temporary or permanent ponds, and slow-moving areas of streams and rivers.“ One of the photos posted on BugGuide looks very similar to the shape of your creature. Another family in the infraorder Gerromorpha is Veliidae, and the inhabitants are called the Broad-Shouldered Water Striders. One image posted to BugGuide from Florida and it is listed as a Marine Water Strider, Trochopus plumbeus. While we do not think that either of the images on BugGuide are your species, we do feel that they are close enough in appearance and behavior to lend credence to our hypothesis. We eagerly welcome more authoritative assistance with this identification.
Eric Eaton provides information
April 19, 2010
The “unknown creature” from the Hawaiian beach is indeed a water strider, possibly of the genus Halobates, which are pelagic (“open ocean”) water striders. There are, however, at least a couple of other genera of marine water striders in Hawaii. The person who sent the image might consult the Bishop Museum in Hawaii to see what they have to say.