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Squash bees are unknown experts in their field (and mine)

Nathan Baker • Jul 14, 2019 at 12:00 AM

Recent visitors in my backyard garden turned out not to be the bees I thought they’d be.

I found them early one morning when checking my raised beds while taking the dogs out for their morning constitutionals.

As I moved a zucchini blossom aside to look for fruit underneath, a winged insect buzzed out of it and flew off into the rising sun. It was about the right size and shape, so I assumed it was a friendly neighborhood honey bee.

The next day, I noticed a few more bees huddled together deep in the cups of the zucchini flowers. Their behavior seemed strange — Don’t honey bees live in hives? — so I decided to do a little research.

It turns out, my backyard bees weren’t honey bees at all, but squash bees, a species I’d never heard of.

Unlike honey bees, which were introduced to North America from Europe in the 1600s, squash bees belonging to two genera, Peponapis and Xenoglossa, are native to this side of the Atlantic. I believe mine belong to Peponapis, which live throughout the United States, Mexico and parts of Canada.

They feed almost exclusively on the pollen of squash, pumpkins and gourds, and have adapted a mutually beneficial relationship with the prehistoric crops cultivated by America’s indigenous people.

Squash bees don’t live in hives and don’t have a rigidly structured social order like honey bees.

They sleep in the deep squash blossoms while they’re closed in the afternoon and evenings and come out to eat and mate when the flowers open in the early morning.

Once a female mates, she burrows into the ground and digs a cavity in which she lays a single egg. She stocks the cavity with enough pollen to feed the larva once it emerges and digs a branch from her original tunnel with another egg cavity.

The larvae hatch, eat the pollen and overwinter underground in a cocoon. The next summer, new squash bees dig out of the ground to start the life cycle again.

Females usually dig their burrows near the plants they’ve chosen for feeding.

I don’t want to disturb the larvae when I clean up my beds for replanting, so I looked under the leaves for a bee-hole in the dirt, but I couldn’t tell my bee-holes from the other holes in the ground.

I found squash bees so interesting because they’re so specialized. They almost literally live, breathe and eat squash. They’ve developed alongside this prehistoric staple crop and have helped it thrive.

Their existence depends exclusively on the nearby availability of a very specific group of plants. They’ve evolved and adapted to be the best bee at feeding on and propagating those plants.

Because they are such early risers, and because their bodies are better suited to transfer pollen between male and female flowers, squash bees present on the site of their specialty crops render honey bees superfluous for pollination. By some insect experts’ estimates, squash bees pollinate two-thirds of the commercially grown squash in the U.S. and are present in small backyard gardens like mine.

If you like zucchini and onions or buy a pumpkin at the store for your Halloween jack-o-lantern, there’s a good chance you’re enjoying the vegetables of squash bees’ labor.

But these bees don’t get the credit they deserve. Honey bees enjoy the limelight — and rightly so, their contributions to our food supply are great — while squash bees are unsung heroes.

Next time you’re in your garden in the morning, take a peek inside your squash blossoms and see if you’ve got any of these hardworking specialists in there. If you see them, let them know you appreciate them.

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