Bee of the Month

Bi-colored striped sweat bee.

May 2021

Bi-Colored Striped Sweat Bee

by Liam Cullinane, former Jeffco ISM Specialist

Photo credit: bugguide

The bi-colored striped sweat bee (Agapostemon virescens) is a very common bee species found in Colorado ecosystems. It is active for nearly the entire growing season from April to October.

The head and thorax of this bee species is brightly metallic green, making it one of the easier native bee species to spot foraging on various plants. It is a generalist and will collect pollen and nectar from a variety of plant families so it is common in urban backyard and parks.

Like all Halictid bees, this species nests in the ground in a variety of habitats (lawns, open fields, hillsides, etc.). It is also a communal ground nester, meaning more than one female will share nest entrances.

However, unlike most social bee species there is not division of labor in these communal nests. Under the nest entrance each female creates their own area of the nest and will lay their eggs in these separate parts of the same nest. While there is no shared labor between occupants of the same nest, communal nesting allows for an increase in protection from predators and other enemies!

Cuckoo bee.

April 2021

Cuckoo Bee

by Liam Cullinane, former Jeffco  ISM Specialist

Photo credit: Penn State Extension

Nomada is a genus of bees that includes over 850 species worldwide. They are some of the most unique bees in terms of appearance and behavior. Bees in this genus are very colorful, ranging from red, to yellow, to black, to metallic or any combination of those. Their wings are also very distinct with a smoky glean near the tops and tips of the wing. Nomada species vary greatly in appearance but are some of the hardest bees to identify to species, and new species are still being discovered and described. 

These bee species also lack hairs that are a common feature of bees. Because of this, their appearance is similar to wasps, and they are often misidentified as such. In addition to their unique appearance, Nomada species also have a unique life history. 

They are parasites of other bee species and have the common name cuckoo bees. They do not provision nests, which is why they are known as nomadic bees (in Latin, Nomada). These bees will travel around looking for their host bee species foraging on flowers. Once they locate them, they follow them back to their nest and lay eggs in the nest of the host bee. The eggs of the cuckoo bee hatch first, and if the adult bee had not already eaten the larvae of the host bee, the newly hatched cuckoo bee will do so. 

Many bee species in the Andrena and Agapostemon genera are hosts of Nomada species. Bees in this genus are active when their host bees are active, so many of them emerge in the early spring. Be sure to look out for them lurking on early flowering shrubs and trees.

Blue orchard bee.

Photo credit: bugguide

March 2021

Blue Orchard Bee

The blue orchard bee is a beautifully colored cavity nesting bee species, active in the early spring to summer. This bee is partially domesticated by humans due to its easy-to-control nesting habits. 

Bees in this species nest in small, already made cavities in wood or other structures, including human-made structures (they are known to occasionally nest in garden hoses or abandoned pipes). Humans have created structures to support these bee species and actively breed them for agricultural purposes. 

Because these bees are active in the early spring, they are important pollinators of trees and shrub species, including important trees for agriculture. Their importance in the agricultural industry is how they derived their common name, the orchard bee. They are particularly efficient at pollinating apple, pear, and cherry trees, but are effective pollinators of many different plant species. 

Be sure to thank this bee species the next time you are eating an apple, pear, or cherry!

Violet miner bee.

February 2021

Violet Miner Bee

Andrena violae 

Violet miner bee (Andrena violae) is a medium sized, pollen specialist bee. Bee species that are floral specialists only collect pollen from plants in specific genera or families. In the case of the violet miner bee, this species collects pollen exclusively from plants in the violet genus (the picture above shows this species on a blue violet plant). Because of this specialization, these bees must time their emergence with the flowering time of violets. As such, they are usually found flying around in early spring from March to April. 

Bees in the Andrena genus nest in the ground in sandy soils, often under shrubs or trees. This species is mostly found in the eastern U.S.; however, Colorado’s unique ecotypes allow this species to persist in relic habitats in the northern Front Range. Be sure to look out for these bees on wild violet blooms in the early spring!

Cellophane bee.

January 2021

Compact Cellophane Bee

Colletes compactus 

Photo credit: bugguide

The compact cellophane bee is a late summer emerging ground nesting bee species. These bees dig long narrow nest tunnels deep into bare soil and then create horizontal off shoots from the main tunnel in which they lay their eggs. This species is a solitary bee, meaning there is only one female bee in each nest. The “queen” gathers pollen and nectar from nearby flowers and creates pollen balls (a combination of pollen and nectar molded into a small ball like structure) on top of which they lay one single egg. Once an egg and pollen ball are placed into the horizontal tunnel, it is closed and sealed off.

Cellophane bees line their nest cells with a material that is waterproof and looks like plastic when it is dry, hence their name, cellophane or polyester bees. These bees have a forked tongue that allows them to create this unique material. In addition to the waterproofing, bees in this genus also line their nest cells with a natural bactericide and fungicide, linalool, for extra protection against diseases.

Although this species is solitary, females have been known to nest in aggregations, so there can be hundreds of bees in the same area. All bees in the genus Colletes are non-aggressive, so these aggregations are a great place to witness solitary ground nesting bees in action!


November 2020 

Tripartite sweat bee

Halictus tripartitus

Tripartite sweat bee is a very small, generalist bee species in one of the most common bee genera in North America (Halictus). Bees in the genus Halictus are the most abundant species of sweat bees, and are some of the most abundant native bees found in ecosystems in Colorado. This species is broadly distributed across North America, with its range stretching from southern British Columbia down to Mexico and from the west coast to Missouri.

Sweat bees derive their name from the unique behavior of being attracted to human sweat, which they drink for its salinity. This species of bee (and all sweat bees) nests in the ground in small holes in bare soil. This particular Halictus species is also semi-social. Daughter bees remain in the nest to assist with brood care instead of colonizing their own nests.  

Tripartite sweat bees are floral generalists, meaning they will visit plants in many different families to collect pollen and nectar. These bees can be seen from spring to early fall, so the chances of coming across this species in open space areas or even in your garden is very high! They are very small and move quickly from flower to flower, so make sure you stay very still and focus on one or two flowers in a large patch to catch a glimpse of these bees.


October 2020

Hunt's Bumble Bee

Bombus huntii

By Liam Cullinane, ISM Specialist

Photo Credit: bugguide

Hunt’s bumble bee (Bombus huntii)  is one of the most common bumble bee species in Colorado. Like many other bumble bee species, it is a generalist, collecting pollen and nectar from a variety of plant families, genera, and species. 

This bumble bee species nests in the ground, in already existing holes (e.g. abandoned rodent burrows, bird nests). 

Bumble bee species are somewhat unique in the bee world in that they are some of the only bee species that are highly social. A single colony of the Hunt’s bumble bee can have around 1000-2000 members throughout the growing season. In the beginning of the summer (March-May), Hunt’s bumble bee queens will emerge from their overwintering nests and begin searching for a new nest to start their colony. 

Once a nest is established, the queen will begin producing unfertilized female worker bees, which are significantly smaller in size than the queen. These workers carry out most of the pollen and nectar collection for the remainder of the season. Colony sizes reach their maximum around mid-summer (June). Then, near the end of the summer, the queen begins producing larger females (presumed to be next year’s queens), as well as male bees. 

At the end of the growing season, the queen, all worker bees, and the males perish, with only next year's queens surviving the winter. 

Make sure to look out for this species in parks and open space areas and in your garden!

Sunflower chimney bee.

September 2020

Sunflower Chimney Bee

Diadasia enavata

 By Liam Cullinane, ISM Specialist

Photo Credit: bugguide

Sunflower chimney bee (Diadasia enavata) is a solitary ground nesting bee species that specializes on a subset of plants in the Asteraceae (Sunflower) family. Bees in the genus Diadasia are often called chimney bees because they create chimney-shaped structures on top of the entrance to their nest. 

Research suggests a few explanations for this behavior. The first is that these “chimneys” prevent debris or other insects coming into their nests. The other explanation is that they use the extra soil to plug their nest holes after they have laid their eggs. 

Bees in this species time their emergence from their nest when their host plants begin blooming (mid to late summer). They are very efficient at collecting pollen from these host plants (as seen in the picture) and provide invaluable pollination services in their ecosystems. 

They are one of the most common and widespread bee species in the Diadasia genus and can be seen across most of North America. Be on the lookout for these bees on sunflower blooms in late summer!

Squash bee.

August 2020

Squash Bee

Peponapis pruinosa 

Squash bee is a solitary bee species that specializes on plants in the Cucurbita genus (squash and gourd plants). Because of this specialization, females only collect pollen from plant species in this genus (summer and winter squashes, pumpkins, gourds, etc.), hence why this bee’s common name is the squash bee. These bees are similar in size to honey bees (although they are a bit larger) and are sometimes misidentified as such, however, squash bee females nest in the ground in well-drained bare soil and males can often times be found resting in squash flowers. A defining characteristic of this bee species is their foraging behavior, collecting pollen around sunrise, when squash plants open their flowers. This bee species occurs throughout the United States and Mexico and is active in the mid-summer (June-August).