ID GUIDE TO WILD BEES - NEW YORK

SQUASH BEES

Squash Bee

(Peponapis pruinosa)  - 2/5" - 3/5" (medium-sized)

Squash bees evolved in tandem with squash plants, which are native to the Americas.  These wild bees are specialist pollinators – their sole hosts are 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 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.

 

Wilson & Carril, biologist-authors of The Bees in Your Backyard, write that squash bees are prodigious pollinators in part because of their habit of rising early, before other bees.  In addition, squash bees are fast fliers, able to visit more flowers per day than honey bees.  Finally, squash bees are large and hairy; their hair collects pollen, and the bees' size provides more surface area to which pollen can stick. These last qualities make even male squash bees excellent pollinators. (In most bee species, female bees alone are equipped with special pollen-collecting hairs called scopae.) It is not unusal to see a male squash bee with pollen coating the hairs of his face and thorax.

 

Wilson & Carril also 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 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.

 

According to the web database Discover Life, squash bees are preyed on by a species of cuckoo bee, Triepeolus remigatus. (This bee is shown in the photo strip at right and also appears in the cuckoo bee section of this guide.)  Triepeolus remigatus bees creep into squash bee nests and deposit eggs there. When the cuckoo larvae hatch, they kill off the squash bee larvae and eat the provisions stored for them in the nest.

​Squash bees are reportedly in decline, in part because of their sensitivity to commercial pesticides. Their specialized function as squash pollinators also makes them vulnerable, since they rarely forage on other plants. The bees do not inhabit Rockefeller Park State Preserve, which has no squash or melon plantings.  Nevertheless, the preserve, which surrounds Stone Barns, serves the important function of shielding the bees from exposure to pesticides.

 

Identification Information:  Squash bees are slightly smaller than the typical honey bee. They somewhat resemble honey bees in form, but are more robust and hairier and have abdomens ringed with distinctly defined dark and light stripes. Squash bees' thoraxes are covered with light-gold hairs.  Their legs are a dark reddish-brown.  Both males and females have big noses, as shown in the photos at right.  Males have pale patches on their faces.

 

Squash bees of the species Peponapis pruinosa are also referred to by the common names "hoary squash bee," "pruinose squash bee" and "eastern cucurbit bee".  The genus Peponapis belongs to the bee tribe Eucerini, also known as long-horned bees.  There are thirty genera (genuses) of Eucerini in all.  Another is Melissodes long-horned bees, shown elsewhere in this guide. 

Squash blossoms
at dawn

A squash bee bathed in the yellow light of a squash blossom

All photos (c) 2014 - 2017 Sharp-Eatman Nature Photography

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REFERENCES:  For a comprehensive list of references used in compiling this guide, click here:

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