Squash bees evolved in tandem with squash plants, which are native to the Americas.  These wild bees are specialist pollinators – they visit cucurbits, that is, squashes, pumpkins, gourds and melons.  The bees’ geographical range coincides precisely with the range of such plants. Although domestic honey bees may be seen at times feeding on the nectar of squash blossoms, squash bees are such efficient pollinators that they generally succeed in pollinating all of the flowers of a squash plant by early morning, before honey bees brought in as crop pollinators reach the blossoms.  Squash bees are exceptional pollinators of zucchini and butternut squashes. 

Squash bees are unusual because of their ability to fly through the dark in order to arrive on host plants before sunrise.  A squash bee's ocelli -- its three small eyes located between its two larger main eyes – are enlarged for this purpose.  Squash bees begin their daily feeding early because squash flowers tend to wilt by mid-afternoon.

Squash bees are excellent pollinators for other reasons.  They are fast fliers, and thus able to visit more flowers per day than honey bees.  Squash bee are also large and hairy; their hair collects pollen, and the bees' size guarantees more surface area to which pollen can stick. These last qualities make even male squash bees excellent pollinators.  It is not unusual to see a male squash bee with pollen coating the hairs of its face and thorax.

In The Bees in Your Back Yard, authors Wilson & Carril detail the interesting nesting habits of these bees. Squash bees emerge from overwintered nests in spring to feed on the nectar of squash blossoms. Initially, both males and females sleep in the flowers. Eventually, the bees mate and the females begin constructing new nests:  they dig as deeply as 1 1/2 feet into the soil, forming tunnels with side-burrows in which the females deposit eggs. Thereafter, the females collect and carry pollen back to the nest, where they overnight and work provisioning the egg cells for the time when the young hatch. The bees then seal off the cells.  After the larvae hatch, they overwinter in their nests, feeding on the provisions left there. In early summer, the larvae metamorphose into bees and sally forth into the warm air just before squash plants begin flowering.

At Stone Barns, squash bees are prevalent in plantings of winter squash and zucchinis. During growing season, the bees can be seen flying from one orange squash blossom to another, or hanging head downwards inside the flowers, their striped abdomens pointing upwards. When the squash blossoms wither under the afternoon sun, the males crawl inside them to sleep; if you uncurl a wilted winter squash or zucchini flower at Stone Barns, more often than not you’ll find a squash bee sleeping there.