Most of what we read in the news about declines in bee populations focus on (non-native) honey bees. Yes, those populations are suffering declines from the combined impacts diseases, habitat loss, pesticide use and other factors. However, there are nearly 4,000 bee species in North America, and many of them are dealing with the same pressures and threats as honey bees. In addition, honey bees are social insects, living in large collaborative colonies of workers and queens. The vast majority of bees in North America, however, are not social, and they succeed or fail on the backs of single moms.
At first glance, some solitary bees might appear similar to honey bees (I’ve certainly been guilty of making that mistake many times) but while their appearance might be somewhat similar, their life stories are very different. This one is a solitary bee in the genus Svastra. At least I think it is…
Solitary bees – bees that don’t live in colonies – are all around us, but they go largely unnoticed. Many escape our attention because of their small size, but others are as big as or bigger than honey bees. Solitary bees can vary greatly in their diet preferences. Some are generalists, feeding on nectar and pollen from a wide variety of flower species. Others have much more narrow diets, feeding only from sunflowers, for example, or other categories of flowering plants.
Most solitary bees in prairies live in underground burrows, though others live in hollow plant stems or similar spaces. In colonies of social bees, the work of gathering food, maintaining and defending the home, and feeding and caring for the kids is split between hundreds or thousands of bees. In the case of solitary bees, the single mom does everything. In most cases, she finds a likely spot, digs a burrow and prepares it for eggs. Then, she flies around the neighborhood in search of the kinds of flowers she can collect food from. As she nears the flowers, she’s likely to encounter males of her species, who basically spend their entire lives buzzing from flower to flower, hoping to find females to mate with.
A male solitary bee (Dufourea sp.) waits for females at a sunflower.
Assuming the single mom can find food nearby, she returns from foraging with a load of pollen and nectar, which she combines into a ball of sticky dough. She places that in a cell within her burrow, lays an egg on or next to it, and seals up the cell. Then, she takes off to repeat the process: find food, mix it together, lay an egg with it, seal up the cell. Later, the eggs will hatch, and the larvae will stay in their cells and feed on the dough balls provided for them until they grow into adults and leave the nest.
As you might imagine, life isn’t easy for single mom bees. They have to gather food for themselves and their kids, while fighting off overly-enthusiastic males with only one thing on their minds. When they aren’t out finding food, they are building and provisioning baby rooms or sitting vigilantly at the entrance of the burrow, defending it from marauding wasps or other threats. After mother bees have filled their burrow with eggs-in-cells, they seal up the whole nest and fly away, hoping for the best.
Single mom solitary bees have difficult lives, but there are ways we can help them. First, we can help ensure the availability of nesting sites. Some ground-nesting bees need areas of bare ground, and many others need at least access to the soil without having to fight through a dense layer of plant litter. Similarly, stem nesters would appreciate it if you didn’t chop down all of last year’s plant skeletons, especially those of raspberry, sunflower, rose, leadplant, and other plants with hollow stems. Providing this kind of nesting habitat is important in prairies and other natural areas, but also in backyard gardens and other urban areas. Because solitary bees aren’t aggressive toward humans, there’s no downside to sharing your yard or garden with them (and, as pollinators, they’ll work for their housing).
A “long-horned bee” (Melissodes sp.) on dotted gayfeather (Liatris punctata).
Perhaps more importantly than housing, what bees need most is food. The key to supporting strong bee communities is plant diversity. A prairie or garden with lots of different kinds of flowers will support lots of different kinds of bees. Specialist bees will be able to find the particular flowers they need, and generalist bees won’t run out of food when one kind of flower stops blooming, gets eaten by insects, or is wiped out by disease. Early spring can be a particularly difficult time for bees to find food because of the relative scarcity of flowers at that time of year. Boosting the spring-time abundance of both native wildflowers and flowering shrubs in gardens and natural areas can be very helpful.
In prairies and other large-scale habitats, it’s important to think about the flight range of bees. Honey bees can travel up to several miles to find food. Most solitary bees are considerably smaller, however, and they may be limited to a range of a few hundred yards or less from their nest. During their nesting season, bees will need to find everything they need to survive and supply their nests from that relatively small circle of habitat. The availability of abundant flowers of many kinds within that circle helps ensure that bees can find food throughout the season. If a large area surrounding a bee’s nest is mowed or grazed intensively, it is left stranded with a nest in the middle of a food desert.
This tiny sweat bee fits perfectly into this puccoon flower (Lithospermum carolinense). Its size gives it access to flowers larger bees (including honey bees) can’t get into, but that size also limits its ability to forage far from its nest.
If you’re a landowner or land manager, think about your property from the perspective of a single mom bee. Pick a few spots on your land and visit them every few weeks to see what the abundance and diversity of flowers looks like. If a bee was nesting where you stand, could she find what she needs for food within a short distance of that location? Are there times of year when it’s hard to find abundant flowers? If so, can you tweak your management or implement restoration strategies to make more flowers available? Are there places where bees can find bare soil for nesting, or is there a layer of thatch covering the soil across your whole site? Burning, intensively grazing, or haying portions of your land each year can help reduce thatchiness and help ensure bees’ access to soil. However, creating patches of prairie habitat representing a full spectrum of vegetation structure types (tall/dense, short/sparse, mixed-height, etc.) will be of maximum benefit to both bees and other insect and wildlife species.
Single mom bees deserve our respect and admiration. They build and prepare their nest, seek out and harvest food while dodging predators and lustful males, and provision their eggs with food and a safe place to grow up. Oh, and along the way, they also pollinate and help ensure the survival of the majority of plants on earth. It seems only fair that we should acknowledge their work and do what we can to help them out.
More information:
While the vast majority of native bees are solitary bees, some are social as well, including bumble bees, some sweat bees, and others. Bumble bees, in particular, are very important pollinators because of their size and mobility as well as their willingness to visit many different kinds of flowers. As opposed to honey bees, whose colonies can survive the winter intact, all bumblebee individuals except fertilized queens die at the end of the growing season. Those fertilized queens overwinter and then become single moms in the spring. Once the queen’s first brood matures, those bees take over the foraging work and take care of the queen. You can learn much more about solitary bees and other native bees here.
Many thanks to Mike Arduser and Jennifer Hopwood for reviewing this post for accuracy. Any remaining errors are mine, not theirs.
The Prairie Ecologist 