Mystery Maggots

Caterpillar, not maggot–see the six true legs and 10 prolegs?

The weather has been hot here, and all the doors and windows stand open all day. With no window screens, that means an array of bugs (and the occasional bird) pops in and out of the house. It’s not unusual to find flies, butterflies, damselflies, etc. on the windows. 

Still, I did a double-take when I saw maggots on my desk the other day. I knew they hadn’t flown in on their own—they must have been hatched nearby. I checked for unseen dead things on the shelves above, but found nothing. There was another maggot this morning, and I did a second unsuccessful check for the source. Then, while I was away from my desk for fifteen minutes, another appeared.

This time I pulled out the microscope and had a closer look.

It wasn’t a maggot at all. It was a tiny caterpillar.

I could think of no reason for a bunch of caterpillars to be living on my bookshelves and dropping onto my desk.

Then I remembered earlier in the day I’d shooed a wasp out of the office several times.

Bingo!

The wasp was a European tube wasp. These little insects seek out cracks and holes to nest in. They fill their nests with up to 20 caterpillars as food for their larvae and then seal the nest with mud.

That would explain the bits of dried soil that accompanied some of the ‘maggots’.

We’ve seen the same thing with our native potter wasps. Last year I had to put tape over all the screw holes in the underside of the dining table, because potter wasps were stuffing them with paralysed spiders (and the spiders kept falling out all over the floor).

As I write, the wasp has returned. Empty-handed this time, she’s fossicking around for a new place to raise her young. Maybe she’ll find one her caterpillars will stay in this time.