Why zucchini needs squash bees to thrive

So much is happening in gardens in July.

Summer is grandly underway, and plants are growing and blooming rapidly. Each week brings new surprises.

In the vegetable garden, memories of all the grinding work of putting in the garden, of pushing wheelbarrow load after wheelbarrow load of compost, of laboriously forming beds, of weeding errant bindweed and Bermuda grass, of assembling all the various components of a drip irrigation system, of tenderly planting a multitude of vegetable starts - have disappeared into oblivion. Now the garden appears to have emerged spontaneously from the ground, and the plants boast of their strength.

Their humble origins are long forgotten and only the future stretches ahead. The seasonal march of the zucchini has begun, and just as you feel caught up, an army of new fruits announce themselves and demand attention.

Our thoughts scour the rank of friends or neighbors who may be potential zucchini recipients, and plots of ambush are laid.

Bouquets of basil, a few cucumbers, a handful of carrots and beets, and a fat bunch of Swiss chard are great disguisers of the zucchini overflow, and act to camouflage and distract from the main purpose of the offering. And yet there are some of us who can’t eat enough of it.

But what pollinates our zucchini? An important and original pollinator of squash and gourds is the squash bee, (Peponapis pruinosa).

It is a ground-nesting, solitary native bee that exclusively gathers pollen from plants in the squash family (genus Cucurbita), including pumpkin and gourds.

The bees may visit other flowers for nectar. Female bees make small burrows in the ground with branching chambers. They gather Cucurbita pollen and form it into balls, then lay an egg on each pollen ball, and repeat this process about five or six times.

The larvae eat the pollen, and then pupate, emerging as adults that summer or the following one. Adult bees feed primarily on nectar.

Squash flowers open at dawn when squash bees are out foraging. These bees make an entrance into the day at dawn and can pollinate all the days squash flowers before honeybees get out of bed.

Squash bees forage until about mid-day, when squash flowers begin to wilt. New flowers emerge each day.

It takes about 6-9 bee visits to pollinate each flower. Cucurbits are completely dependent on bee visitation for pollination as male and female flower reproductive parts are held in separate flowers. Pollen is heavy and held deeply in the voluminous flowers and does not blow in the wind. Before the introduction of honeybees by Europeans, squash bees pollinated indigenous people’s squash and gourd plants throughout the Americas.

Squash bees are found throughout much of the United States and into eastern Canada and are easy to identify.

Simply go out early in the morning and peer into your zucchini flowers. What you are likely to see are the boy bees, who sleep in the flowers while the industrious females sleep in their hard-dug burrows.

Sometimes there will be a conglomeration of four or five boy bees peering back at you. Don’t worry, solitary bees are not defensive and male bees have no stingers. As the flowers wilt at around noon, the males sleep in them (They are able to chew their way out).

The female bees roughly resemble honeybees, but they are slightly larger, broader, have longer antennae, and have very hairy hind legs that loose pollen adheres to. If they are carrying pollen, the hairy legs will be very noticeable. Males do not collect pollen and have a yellow dot on their faces.

Squash bees’ nest in the ground near squash plants. The exterior of the nest may resemble a messy ant nest until you see a bee going in and out. Squash bee nests are a good reason to adopt no-till methods in your vegetable garden. Tilling destroys the nests and the bees in them.

There are many surprises awaiting us in our gardens.

Kate Frey’s column appears every other week in Sonoma Home. Contact Kate at:,, Twitter @katebfrey, Instagram @americangardenschool

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