Small Water Scavenger Beetle

2013 July 6

So, we’d all come back from a walk in the woods on July 31,2012, and I noticed this little beetle stuck in Sandy’s hair. It was only about a quarter-inch long.

This was another one that I couldn’t find myself, so I submitted to BugGuide for ID. It turned out to be one of the smaller Water Scavenger Beetles. V belov was of the opinion that it looked like Hydrobius fuscipes, a very common beetle that typically lives around forest pools that are filled with leaf litter. But, Tim Loh decided that it was actually Helocombus bifidus, a very similar beetle that lives in the same habitat, but that has longer maxillae and a different pattern of striations on the wing covers.

Part of the reason I had a hard time finding it was that it didn’t occur to me that it was an aquatic beetle, given where I found it. Although, they do fly, and we were walking near a swampy area at one point, so it probably flew into Sandy’s hair somewhere near the swamp.

Water scavenger beetles eat decaying aquatic debris as adults, but the larvae are predatory. There is a rather graphic description of the larva’s feeding habits here. I quote:

“In water they catch floating prey with their clamp-like mouthparts (mandibles), hold them tight and swim with the living prey intact to the water’s edge. Having found a good landing point, they put their abdomen on the solid ground and move themselves backwards with tracking the prey over the shore. They crush them with their mandibles. The exoskeleton of the prey gets covered over and over again with intestinal secretions. The prey is then kneaded into a pulpy mass which can be sucked up by the larvae. This takes 2-3 minutes. Finally the larva leaves the emptied skeleton and creeps forward back into the water. Cannibalism can become so prevalent among the larvae that they prefer to eat each other than to attack other insects.”

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