Chimney Bees

Watch your feet when out hiking! Oh, it’s not a matter of rattlesnakes or the odd cactus pad. No, it’s that odd cluster of round holes in the trail ahead, far too small for gophers, but clearly made by some living creature. Even odder, some of the holes project above ground like tiny chimneys. And there’s one that curves over at the top in the manner of an old ocean liner’s ventilating funnel. Weird!

These holes are the work of chimney bees. We have a couple of species here. One specializes in collecting pollen and nectar from sunflowers and the other from cactus flowers. They look like fat, hairy honey bees, but are even more yellow, and the pollen collecting system on body and legs is absolutely maxed out. They might as well be wearing chaps. Amazing!

Chimney bees belong to one of several families of mining bees and wasps, in this case, ones nesting in bare ground. Because the ground used is hard, saliva is often mixed into the soil as a softener and as glue to construct the distinctive chimneys of the genus. A single bee may make several nesting burrows. Brood chambers at the end or the burrow and along its sides are provisioned with balls of pollen for the larvae to eat once the eggs hatch. Though these are solitary bees, each to its own, they are colonial and a patch of ground may have dozens of holes within a fifteen or twenty-foot radius.

But why a chimney, you may ask? Good question, and though I don’t know the answer, I am willing to guess it has to do with predators and parasites. There are many critters that prey on or parasitize bee broods. These enter the nesting burrows and lay eggs, take larvae, feed on the pollen found or carry out similar nefarious deeds. At least that’s our moral take on such actions.

I rather doubt the chimneys do much to deter those species. But bee flies do not enter the nest of their victims. Rather, their eggs are delivered in flight, either flipped into, or deposited near, nest entrances. When a bee fly’s egg hatches, the larva must find the host bee larva where it is hidden in the burrow. For the bees, the chimney may be just the kind of barrier natural selection has “in mind.”

So look around and down next time you are out. Those little holes in the ground have stories to tell. Stop for a moment and take a read.