Have you ever been dive-bombed by a tree swallow? When I went out to the garden one time, years ago, to harvest greens into a colander, a swallow kept swooping just above me. I put the colander on my head and fled for the house. The greens could wait.

This year, a pair of swallows is nesting in a bluebird box alongside our driveway and near our Christmas trees. They don’t seem to mind the moving traffic in the driveway — wheeled or on foot — but when I stopped to photograph them, I was, once again, dive-bombed, but never actually hit.

In the evening, when I’m pruning the Christmas trees several feet from the nest box, the swallows keep me company, flying above and catching insects on the wing. This damp year, the insects are abundant and the swallows must be well-fed.

What do they eat? According to an Environmental Protection Agency report at epa.gov/ne/ge/thesite, “Tree swallows feed primarily on emergent aquatic insects that can potentially assimilate sediment-associated contaminants.” A good reason to eliminate the contaminants…

Prey, said the EPA, usually ranges from 0.04 to 1.7 inches and includes Diptera (flies, 46 percent), Homoptera (“true bugs,” including aphids, scale insects, cicadas and leafhoppers, 26 percent), Ephemeroptera (those ephemeral Mayflies, 11 percent), Odonata (dragonflies and damselflies, 5 percent), Coleoptera (beetles, 4 percent), Molluska (molluscs, 4 percent), Aranae (spiders, 2 percent), Psocoptera (booklice and barklice, 1 percent), Hymenoptera (sawflies, wasps, bees and ants, 1 percent) and small amounts of other orders of insects.

Those Diptera that make up 46 percent of tree swallow insect catches include mosquitoes, gratefully. They may also include midges, some of which feed on Christmas trees and others of which compete with the midges that feed on Christmas trees.

And the Odonata — dragonflies and damselflies — that the swallows consume: They may have eaten some of the bugs that affect Christmas trees. Plenty of Odonata remain, despite the swallow family’s persistence.

I cheer the swallows for eating the bugs that bug me or that bug the trees, but wonder at the complexity of the ecosystem out there, and in the end just trust in nature to keep different life forms in balance. So far, things are working fine.

Tree swallows are also frugivorous — they eat fruit. The berries of the Myrica family, including bayberry (M. pensylvanica) in the north and wax myrtle (M. cerifera) in the south, are coated with a wax that swallows can metabolize, and I have seen tree swallows de-fruit a bayberry hedge in late summer afternoon as they switched their diets from insects to fruits to gather energy for their migration.

Perhaps tree swallows are responsible for the spread of bayberry shrubs within our Christmas trees. (And when the shrubs don’t interfere with tree growth, we leave them there.) I started several bayberries from seed when we first moved here almost 30 years ago, planted the seedlings around the house and in our little orchard, and stood back. About 10 years later, I started seeing bayberries popping up in our landscape, and even along the side of the road up to a quarter of a mile away.

You never know what you might start when you plant a seed or put up a nest box.