Sweat Bees are one of the smallest, socially diverse and commonly-found bees in North America, aside from the Honey Bee. The average size of this species is 5-10mm in length. Several species of Sweat Bees we’ll hone in on were found at the Bee Sanctuary and Research Garden on Governors Island, NY.
Photo above by David Alexander.
Known for their striking green iridescence, Pure Green Sweat Bees (Augochlora Pura), are solitary bees, native to the eastern United States. The tiny bees (8mm long) of this species have a highly sculpted exoskeleton, called a carapace, which varies in an array of striking colors - from green to gold to blue. From the head, thorax and abdomen, their carapace are covered in many punctures. Males can be distinguished from females through some slight variations: males are typically smaller and have one additional antennal segment than females. Adult female Augochlora also have pollen-collecting hairs (scopa) on their hind legs, whereas males do not.
Metallic Dialictus Sweat Bees are very small bees that also have a metallic sheen to their bodies, which range in colors blue, dark green or bronze. Most Dialictus species are nearly impossible to differentiate between another. Some are covered in fine, pale hairs - such as the distinctive Hairy Lasioglossum - with a thick coat of tan hairs covering its abdomen and a bronze-gold thorax. If spotted in the garden, one might describe it as pale gold and fuzzy.
Photo above by Missourri Department of Conservation.
The New-York-native, Ligated Furrow Sweat Bees (Halictus Ligatus), are 7-10mm in size (smaller than the head of a dime), primarily brown-black in appearance with defined bands of pale hair on their abdomens, but lack the metallic sheen of their sister species. Female Halictus have dark mandibles and legs, with pale fur on their hind legs, while males are distinguished by yellow legs and partially-yellow faces with mixed red-brown mandibles. There are 25 species of Halictus in the Americas, six of which reside in the state of NY.
Adult Sweat Bees are ground dwellers that construct their nests in vacated insect burrows and moist, rotting wood or find temporary housing within logs. This species is utterly independent - in particular, the females do not rely on males in any way aside from fertilization. To females, their nests are fortresses of solitude, which they will fight to defend. It has been observed that females will treat even their newly-emerged offspring as intruders in their nests. The females have powerful jaws with which they don’t hesitate to use to physically remove an unwanted house guest.
However, Halictus Ligatus (Ligated Furrow Bee) is a family of Sweat Bee that burrows or mines into the ground to build their nests for colonies. Their behavior is distinctive from other Sweat Bees, in that they are eusocial beings with very diverse social behavior, ranging between both solitary and communal colony nesting. Within colonies, female Halictus use aggression to establish social hierarchy and coordinate division of reproductive duties. They also overlap generations in one season - unlike other Sweat Bee species.
Photo above by Imagine Our Florida.
This species is active from spring through fall, while those living in temperate, southern climates can be found throughout the year. Males are most active in the spring and only survive one season, dying in the fall; for this reason, females typically outnumber males by the end of a season. Females born late in the season usually live through one winter - referred to as ‘overwintering’.
As their name suggests, female Sweat Bees are attracted to human sweat and will consume it for its salt content, although males typically do not. Adult Augochlora collect pollen from flowers for their offspring and pick up small amounts of nectar to consume for themselves. Over 20 families of flowering plants can be pollinated by Pure Green Sweat Bees.
While being generalist pollinators, Sweat Bees are essential wild pollinators of a wide range of (commercial) crops, fruits, native flora and fauna. Halictus Ligatus are key pollinators of commercial sunflowers. Additional plants you might consider adding to your garden include:
Adults pollinate in forests and the adjacent fields or prairies. Up to 90% of the Sweat Bee population can be found in the canopies of wooded areas in the eastern U.S. Likewise, there is reason to believe this species is one of the few pollinators of the walnut.
Photo above by: Standing Outinmyfield.
Do they sting? While typically gentle, only female Sweat Bees can sting, and will do so only when feeling threatened.
Do they produce honey? This species of bee does not produce honey.
It’s important to remember that Pure Green Sweat Bees are native pollinators in eastern deciduous forests and are often found in or outside of wooded areas. This species has the capability to be pollination powerhouses in orchards or crops adjacent to wooded areas. One way we can help Sweat Bees survive is by leaving rotting or fallen trees for them to make their homes, unless the trees are hazardous. Unfortunately, it is common for the shallow nests of Sweat Bees to be easily destroyed by accident. A DIY way we can help maintain a safe habitat for Sweat Bees is by creating a dedicated area of loosely-covered, sandy soil, in a sunny spot, to provide them with optimal pollination conditions. Other ways to support their livelihood is to:
Photo above by Yardious.