Star magnolias were blooming at the Toledo Botanical Garden, and I wondered: would the mining bees be active?
Two years earlier, I was at the Botanical Garden teaching a Master Gardener class in early spring. On a lunch break, I took a walk and was amazed to encounter hundreds of busy mining bees beneath the still-bare canopy of a giant oak tree.
The bees were flying about 10 inches from the ground, darting back and forth then tumbling together to mate. Incoming bees would crawl down into holes in the ground, then fly off minutes later. Mesmerized, I spent the better part of the lunch break watching and photographing the bees, then returned with the Master Gardeners to show them these solitary native bees.
On a return trip this spring, two years later, the timing was identical. Star magnolias, daffodils and early rhododendrons were in bloom. I wondered, would the bees reflect the same phenology and again be active? As I walked to that same oak tree, I was excited to see small soil volcanoes (tumuli), indicators of active mining bees. Dozens of bees were in flight just above the soil surface, mating and tumbling as their grandparents had done two years prior.
Many gardeners have never seen or noticed solitary ground nesting bees, and are amazed to learn of their life cycle. Even experienced naturalists I met at a recent nature conference were surprised to notice bees flying in the soil near a sidewalk, having dismissed the small soil volcanoes as the work of ants.
Each solitary female bee returns to the place where she first emerged from the ground to prepare the ground tunnels for her offspring. The soil volcanoes are the work of these female bees as they drag and shovel soil out of the tunnel’s entrance.
Before you dismiss the idea of ground-nesting bees by lumping them with painful memories of being attacked and stung by “ground bees,” let me promise you that solitary ground nesting bees rarely (if ever) sting. Solitary bees have neither honey nor offspring to protect, and will only sting if threatened (as in held in hand).
The “bees” from your painful memories could be bumble bees, which do nest in the ground and will sting to protect the nest and offspring. Yellowjacket wasps, however, are the most likely culprit of the ground nesters to attack and sting. Both bumble bees and yellow jackets are social insects, meaning they have a queen and workers in the nest whose job it is to protect the nest from predators and stumbling human intruders. Workers send out alarm pheromones to their sisters, so the unfortunate intruder may be stung multiple times by multiple workers.
Solitary ground-nesting bees are, literally, completely different animals. These docile bees have no queen and no social structure. Each mated female works alone to gather food and prepare chambers called brood cells.
What we can’t see below ground is a network of tunnels and cells, reaching a foot or more deep and wide. Sometimes described as resembling a cluster of grapes, the tunnels branch off to individual brood cells. The female gathers pollen and nectar to make so-called bee bread — food for her offspring — then lays an egg in each cell.
With a bit of luck, each female may provision a dozen cells each spring; she dies shorty thereafter. The bee offspring hatch and feed on the food underground, usually taking the better part of a year to complete their development to emerge as adults next spring. These new adults mate, then females provision cells and lay eggs to complete the life cycle.
Mining bee is a general term for a number of different solitary ground-nesting bees, including the so-called cellophane bee that lines the nest with a waterproofing substance secreted from the female’s abdomen. Some mining bees nest along stream banks (where waterproofing comes in quite handy), while others nest along well-drained south-facing slopes with sparse vegetation. While these are solitary bees, they may nest communally in suitable nesting sites.
Andrenid bees make up a large group of small to medium-sized mining bees, with around 100 species in our region. Many of these bees have a specific diet, preferring a narrow group of plants (asters for example), while others are less choosy in their taste and will forage on many available flowers. Most andrenid bees are active early in the spring, and are considered important pollinators of apples, wild blueberries and many other native plants.
Gardeners sometimes notice mining bees nesting in sparse turfgrass. While it’s sometimes thought that the bees are damaging the turf, the more likely scenario is that the soil is sandy and dry, creating a suitable nesting habitat for the bees but difficult growing conditions for turf grass. Since the bees are important early-season pollinators and will only be active for a month or so, the best advice is to let them bee.
Denise Ellsworth directs the honeybee and native pollinator education program for the Ohio State University. If you have questions about caring for your garden, contact her at 330-263-3700 or click on the Ask Denise link on her blog at www.osugarden.com.