Colourful beetle's strange egg-laying habits

Near the summit of Mount Coot-tha earlier this week, I found a beautiful orange beetle with black spots. My first impression was that it was a leaf beetle in the Chrysomelidae family, and looking up the Brisbane Insects website later confirmed not only this, but its membership to the Cryptocephalinae subfamily, with a tentative genus placement of Cadmus.

I often find it more helpful to learn about insect families, subfamilies and tribes than it is to have a narrow focus on genus and species, and that was the case with this beetle. Reading the Hangay and Zborowski (2010) field guide to Australian beetle families, I was informed that when the female cryptocephalinid beetle lays eggs, she coats them in faeces which then become a shelter-providing case that each larvae lives inside of. This caught my attention because when I examined the photos I had taken of the beetle I had seen, I could see it was depositing large droppings onto the dead stump, and it turns out these may have actually contained eggs.

In Australia, adult cryptocephalinids feed mostly on eucalypts and acacias, but the larvae eat dead plant material on the forest floor, so seeing the adult beetle so close to the ground is perhaps another sign of egg laying activity.

When I uploaded this sighting to my iNaturalist Australia account (@christianperrin), another helpful user provided a link to a fascinating series of observations on the larvae of a British cryptocephalinid beetle. If you care to learn more, just click here.

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