The Wonderful Worlds of Native Bees
With spring's return, we have more than just plants pushing up shoots: native bees are on the wing! Most bee species - close to 90% by current estimates - live a solitary life and do not form social colonies like Bumble bees and honey bees. Unlike Bumble bee species here, Honey bees are not native to North America, but instead hail from Eurasia. Interestingly, though perhaps not too surprising considering their history of coevolution, studies have found that native bees are better pollinators for native plants than Honey bees.
In the first weeks of the spring season, every Bumble bee you see is a young queen, usually in search of a site to set up her nest, flying low and investigating old burrows and other cavities. Not long ago I watched one such queen crawl into an opening in the leaf litter near the base of a mature Late Boneset plant in our garden. Evidently it wasn't up to snuff by her standards, because within seconds she lifted off and flew away to continue the search. Once her nest is established and eggs have hatched, the female workers take over nectar and pollen gathering duties while the queen focuses her energy on rearing more workers. In the fall, a new crop of young queens and males will be born and emerge from the nest to mate. The males die off after mating and the nascent matriarchs bed down in interstitial spaces between the leaf litter and soil to hibernate for the winter, awaiting the new spring and the renewal of the cycle.
Bumble bees are generalist foragers, meaning they gather nectar and pollen from a wide variety of plant species. We've observed them on most of our plants in the garden. They have long tongues, giving them the ability to drink nectar from deeper flower shapes, as well as from smaller flowers. And they are also physically stronger than other bee species, so they are able to pry apart closed flowers like those of Bottle Gentian and Turtlehead.
While Bumble bees are some of the largest and most charismatic native bees, at the other end of the size scale, we have small bees like the Yellow-faced Bees pictured at the top of the page, which can be as small as a few millimeters in length. Talk about tiny! Until I took some close-up pictures of them, I had no idea they were bees. I figured they were small flies or gnats. They are also cavity nesters like the Bumble bees, but they nest in hollow stems or other smaller cavities in rocks or wood. In spring, we see them on the flowers of our Golden Alexander and later, in summer, on Rattlesnake Master, Boneset, Rose Milkweed, and Great Blue Lobelia.
In contrast to Bumble bees and honey bees, they are a solitary nesting species, meaning females provision their own nest with food resources. They line their nests with secretions from their salivary gland that waterproof each of the cells in which they lay an egg. Considering one of their favored nesting places is in hollow stems, you can help Yellow-faced Bees by leaving older perennial stems standing from the prior year. The benefit of stems over things like bee hotels is that the stems degrade over time and are not often re-used as nests for that reason, whereas diseases and parasites can become a problem with permanent bee hotels.
Another common set of native bee species is the Metallic Green Sweat Bees (genus Agapostemon), which are a really stunning sight. They tend to forage on plants like Golden Alexander, Penstemons, Boneset, Ironweed, Vervains, including Hoary Vervain, and Coneflowers like the Purple Coneflower pictured above, and Yellow Coneflower. These species nest in the ground and can produce one or two generations here in the Northeast. The male Metallic Green Sweat bees do not live to overwinter, whereas the young females, similar to new Bumble bee queens in the fall, overwinter underground.
Long-Horned Bees (genus Melissodes) generally forage on aster family plant species like Sunflowers, coneflowers, Joe Pye, and Ironweeds. They're called 'Long-Horned' because they have very long antennae. Like the photo above shows, males often overnight together (quite adorably!) on flowers in aggregations. There is also a species in the genus, called the Denticulate Long-Horned Bee, that specializes in harvesting the white pollen of the Ironweeds (genus Vernonia), including New York Ironweed. Their larvae require Ironweed pollen in order to mature properly. If nothing else, the existence of species that specialize in harvesting pollen and/or nectar from specific plant species is a great reason to plant as diversely as you can.
Female Leafcutter Bees (genus Megachile), as their name suggests cut pieces out of leaves, just like they did to our Spicebush above. They use their sharp mandibles to do the cutting, and bring the leaves back to their nests (in stems or other cavities). They cap each cell that contains a larva and its provisioned nectar and pollen with the circular sections of leaves that they cut (see the Leafcutter female below).
Fascinatingly, at least one study showed that the vast majority of leaves gathered by Leafcutters were from plant species whose leaves have antimicrobial properties. Most of the Leafcutter species overwinter as larvae and develop into adults in spring.
Some of the most fascinating bee species are known as cuckoo bees, like the one pictured above (genus Coelioxys). They're cleptoparasites, with females that do not build their own nests, but instead sneak into other bee nests (in the case of Coelioxys, other Leafcutter species), and deposit their eggs in the nest cells by using the sharp spike on their abdomen to break through the plant material with which Leafcutter's line their nests. The resulting cuckoo larva then kills the Leafcutter host's larva or egg in the cell and uses the food provisions that the host had installed to develop into an adult. Talk about a brutal strategy!
There are way more bee genus/species than can be discussed in a quick post. These are just the most common that we encounter in our garden. For a better, more expansive discussion, please check out Heather Holm's wonderful book Bees: An Identification and Native Plant Forage Guide (2017), which I used as a resource for this post. She details each major genus, their seasonality, reproduction habits, active period(s), and their most common native forage plants for the Northeast, Midwest, and Great Lakes regions. It's truly a fantastic resource.
And with that, happy bee-observing in the garden!
-Andrew