Saturday, August 6, 2011

Aquatic Beetles in a Wheelbarrow

When I think of beetles, what comes to mind are ladybugs, ground beetles, fireflies...maybe stag beetles. All of these are terrestrial beetles and are pretty neat, but why stop at land? There are a number of aquatic beetles that are just as cool, and can be found in rivers, streams, and standing water.

I was canvasing my yard the other day when I came upon a wheelbarrow that was full of standing water. I've checked it a few times before for insects, but usually only find mosquito larvae. Last summer I did find one aquatic beetle, but I never got around to investigating what it was.

When I checked it this time, however, I found a much more diverse assemblage of creatures.

 Acilius mediatus

The orange you see in that picture is rust, while the green gelatinous stuff is an egg covering from one of the species of aquatic beetles in the wheelbarrow. Either that or it's algae or something similar. The beetle Acilius mediatus is in the family Dytiscidae, the predacious diving beetles. You can see its hindlegs, which it uses as oars to swim through the water. I watched the beetle for a little while, and from time to time it would swim up to the water surface, thrust the back of its abdomen out of the water, then swim back down to the depths, hiding under debris. By doing that, the beetle grabs an air bubble and traps it under its elytra, using it as a physical gill. That's wild! The word for this bubble is also one of my favorite biology terms: a plastron. 

A brighter picture, with size comparison to a penny. The beetle about 12 mm long.


This isn't the clearest picture, but you can see more of the green gelatinous stuff. You can also see small black beetles. I'm not sure what those are, so I'll probably collect a few specimens soon.

 I was also able to learn a little more about the aquatic beetle I saw in the wheelbarrow last summer and collected one of them. Contrary to what I thought at first, the second beetle is NOT in the family Noteridae. Rather, like the previous beetle, it's in the family Dytiscidae.

 A small beetle, only about 5 mm long.


This beetle also has its hind legs modified for swimming, and utilizes a plastron as well. It might be in the genus Laccophilus, but that remains to be seen. UPDATE: This beetle is indeed in the genus Laccophilus, it's the species Laccophilus fasciatus.

As I was watching these beetles, I started wondering how they got into the wheelbarrow in the first place. I hadn't figured it out, so in the meantime I was trying to get a better picture of the beetle I collected. I had it in a small dish of water and picked it up, causing it to slide around frantically in my hand. 

Then it spread its wings and flew out of my hand. 

Oh. 

So that's how they get around to new bodies of water. Yeah, that makes sense. 

Beetles in the family Dytiscidae are predacious in the adult stage, so who knows how much longer they'll all be alive. Especially the smaller beetles, with that huge Acilius mediatus hanging around. I'll have to go back in a few days and see.


Unfortunately, this treehopper (Membracidae: Thelia bimaculata) was not able to thrive in the aquatic environment as well the beetles do.

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