More Fungus Beetles, Please

Cast-off exoskeletons of the pleasing fungus beetle pupae (Gibbifer californicus),
Imagine them hanging straight down — I turned them up to catch the light.
They are not quite an inch long.

A number of ponderosa pine trees around the house have died from mountain pine beetle infestation, the real culprit being the blue stain fungus that the beetles carry.

I had my eye on one large dead tree as a firewood source, mainly because it was next to the little dirt road that goes up in back. The woodpile was shrinking early last spring (the snowiest time of the year in this area), so I felled it. Just its top and thick limbs were enough to get us through — the rest I cut into rounds and stacked by the road.

Pleasing fungus beetle (Jeff Mitton)

Then warm weather came, and I procrastinated on bringing the rest down until last month.

Whereupon I found these cases on one of the split pieces — but what were they? I turned to What's That Bug, linked in the right-hand sidebar under "Resources."

Very soon I learned that they were the cast-off exoskeletons of the larvae of the pleasing fungus beetle, Gibbifer californicus, of the family Erotylidae, Pleasing Fungus Beetles. (Don't ask me, "pleasing to whom?")

The pleasing fungus beetle develops on soft conk fungi on aspen, ponderosa pine and other logs in forested areas. The biology of the insect is largely unknown; some apparently spend the winter in the adult stage laying eggs in spring; others survive as larvae within the fungus.

The larvae feed on the fungus during late spring and early summer, consuming large quantities. When full grown the larvae hang from the underside of the logs and transform to a pupa, often in groups of several dozen. With this habit, a grouping of pupae may appear some what like a miniature bat roost.

As larvae, they look like this. You can see how that matches the photo above.

As adults, they "feed on nectar, pollen and the bracket fungi growing on rotting logs. Larvae feed exclusively on the bracket fungi, so if you want to see adult and larval pleasing fungus beetles, search rotting logs with bracket fungi," writes University of Colorado biology professor Jeff Mitton.

I am pleased to know this now.