Sandy Gilliam brought by this nest of a colony of bald-faced hornets (Dolichovespula maculata). The nest was attached to the wall of his barn.

Bald-faced hornets are well-known for the vigorous defense of their nests, a strategy that often follows the Bush Doctrine of pre-emptive strike. Unlike honeybees, the female wasps can sting repeatedly without harm to themselves.

But this nest had no angry occupants. It was abandoned last year when the winter set in. This is part of the normal life cycle of the species: a solitary female starts a nest in the spring, builds a large colony through the summer, then the whole colony dies except for young queens who overwinter alone.

A glance at the nest’s entrance (located at the bottom tip of nest) shows that this is a special nest. Straw and feathers protrude. We can peek into the opening and see a tunnel of dry stems.

The nest was built against a wall, so it has no backing. Now that the nest is down we can easily see inside: another nest! House sparrows had climbed into the old insect nest, added some bedding of their own, then set up shop to breed.

This was a stroke of avian genius. No chipmunk or squirrel would be stupid enough to try to raid this nest. (In the tropics, some birds take this further, protecting themselves from raiding monkeys by nesting next to active wasp nests.) The nest also comes with its own insulation system. The hornets build multiple layers of cellulose around the core of their nest, allowing them to stay warm through the night and thereby start work earlier than most insects (see The Thermal Warriors by Bernd Heinrich for more on the the various ways that insects manipulate their thermal environments). The incubating mother bird no doubt benefited from the extra warmth.

The nest retained its old comb, revealing the hornets’ kinship with bees. Here are the hexagonal arrays again, but this time built from chewed wood, not wax.

Entomological enthusiasts should note that although we call these insects “hornets,” they are more accurately called “wasps” or “yellowjacket wasps.” True hornets belong to the genus Vespa and have bulkier heads and abdomens than the more slender “yellowjacket” species (Dolichovespula and Vespula).

I’ll close with my thanks to Sandy for bringing this remarkable nest-in-a-nest to my attention.