Predaceous Diving Beetle (from lower Michigan)

2014 August 9

On July 30, 2013 we were downstate visiting Sandy’s parents (near Manchester), and Sam found this moderate-size beetle (about half an inch long) swimming in a mud puddle.

It looks to me like a Predaceous Diving Beetle, family Dytiscidae.

As it happens, I just got a new reference book this week, “Beetles of Eastern North America”, by Arthur V. Evans, so let’s see if we can find it in there.

Hm. Well. The color scheme looks most like the genus Coptotomus, but the example of that genus in the book is more elongated than this specimen. Aaand, following up on BugGuide, it says “genus needs revision mainly because of high morphological similarity between adults of various species and possible hybridization/intergradation of individuals once deemed as separate species”. Which pretty much translates to “don’t bother trying to narrow it down to species, because even the experts don’t agree on exactly which is which”.

The last time I had pictures of a beetle in this family, it was a dried specimen that had lost most of its legs, and I commented that the forelegs were probably enlarged to aid in grabbing prey. But, in this specimen, the forelegs look pretty unexceptional.

I’m seeing some suggestion that there are only a few species in the family with the enlarged forelegs, and even then it is only the males. But anyway, these have fiercely predatory aquatic larvae like this one that I photographed years ago, and are one of the things that are very helpful for keeping down mosquito populations.

5 Responses
  1. Katbird permalink
    August 9, 2014

    This is a place where some sort of scale would be helpful- what’s the weave size on that tablecloth or paper towel?

  2. August 10, 2014

    Katbird: this was a moderately-large beetle, roughly a centimeter long.

  3. August 12, 2014

    The streamlined shape f the bug got me searching for 1950’s camping trailers, thinking there was a similarity. Then I hit the jackpot.

  4. August 12, 2014

    “of” the bug, not “f” the bug. I think the bug is just fine and does what it was meant to do. I would in no way hurl invectives at it.

  5. August 13, 2014

    KT: Well, that’s a relief. I’d hate to think that you had suddenly taken a dislike to inoffensive beetles like this one.

Comments are closed.