Saturday Critters: Chrysomelid beetle larva

Case-bearing Beetle Larva

This is a photo of an exciting find for my late husband and myself. It wasn’t just a lifer (bug hunters have lifers, just as birders do), it was one of an entire subfamily that I had never known, let alone seen. We all know leaf beetles to some extent: seed beetles, tortoise beetles, calligrapha beetles, the Colorado potato beetle, flea beetles, even lady beetles. But this is the larva of another: a case-bearing leaf beetle: “Larvae are casebearers, living in and protected by a case constructed of their fecal matter and sometimes plant debris. The case is shorter than the larva that remains folded inside it. Eggs are laid in carefully sculpted packets formed from feces and abdominal secretions. . . " (1)

I saw this minute lump, or dot, on an alder leaf in the top photo with my finger tip for scale. A flea beetle was inspecting the lump. I could tell immediately that this was a living creature because of the color and pattern on the dot. I did some shots, took the leaf, and carried it home for inspection. We had a great time figuring out what it was: we went through sawfly larvae, spiders (at one point, it looked like spider legs coming out of the case), until finally, after all the photos and observations, I thought of case bearers. Some case-bearers use leaf litter to construct their cases. This case-bearer uses its own poop (frass).

The only case bearers I knew of at that point were moths, but I searched for others and found Cryptocephalinae. Discovering the ID of a new-to-me insect without help from scientists is one of the most exciting things to do. Of course, what those entomologists have taught me through discussions of their finds and of my photos is what prepared me to be able to figure this out.

I kept the larva in a mason jar with alder leaves for a while but I didn’t like how the life cycle was progressing so I set it free. Unfortunately, I have never found another. I so wanted to see the adult. We could have identified which leaf beetle it was.

By the way: if anyone is interested in insect hunting, I suggest investigating groves of alders. They sustain a huge variety of insects and, therefore, the birds, especially warblers, are there to feed on them.

References: 

1. Bugguide: Subfamily Cryptocephalinae - Case-bearing Leaf Beetles

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Viewing Nature with Eileen

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