On a sunny day a couple of weeks ago, I stumbled on a nesting aggregation of mining bees on campus, in one of Trinity’s campus “biodiversity” areas. In excitement, I rushed to tell my adviser, Jane Stout, only to discover that she and Cian White had simultaneously discovered it and rushed to tell me! Together, we went back to the aggregation to admire the busy bees zipping around in their aggregation, mating, and crawling into their nest holes covered in pollen.
Figure 1 Mating mining bees
On both sides of us, students and visitors walked past without noticing the aggregation. Mining bees are small, inconspicuous insects and are completely harmless. In fact, we have nicknamed them “tickle bees” in the States, as their stinger cannot penetrate human skin.
Figure 2 A beautiful, freshly emerged, female mining bee (Andrena haemorrhoa).
Mining bees are solitary, meaning they do not form a hive. There are no workers or queens. Instead, each female digs into the ground and makes a ball of pollen and nectar on which to lay an egg. Each nest cell contains one pollen ball and one egg and after each cell is completed, she seals it off and starts a new nest cell. Each pollen ball requires many foraging bouts.
Figure 3 Male mining bee.
You may be wondering why these bees form nesting aggregations if they are solitary. I like to think of these aggregations like apartment complexes. Each bee has her own home and they don’t share any of the work, but they live together in the same area. There may be different reasons for this: for example, there may be safety in numbers, or the soil conditions might just be perfect in this area. We don’t really know why aggregations form for sure, but we do know that they’re easier to find than when a bee forms a nest all by herself!
Of course, these bees are not perfectly safe, even in a large aggregation. As we observed them, we also saw that their cleptoparasites were flying around in the aggregation. Cleptoparasitic bees are bee species that don’t bother collecting their own pollen. Instead, they lay their eggs in the nest of another bee. Like the cuckoo bird, these cuckoo bees rely on other species to do all the difficult nest building work.
Figure 4 A male mining bee (left) next to a cleptoparasitic/cuckoo bee (right).
Figure 5 A cuckoo bee hanging around the aggregation.
But not only are these bees beautiful and interesting, they are also incredibly important pollinators. As my work in New York apple orchards showed, they provide the bulk of pollination services to apple blossoms in the Fingerlakes, even when farmers invest quite a bit of money to rent honeybee hives. You see, the foraging behaviour of honeybees and solitary bees differs; because honeybees need to make honey for the winter, they do not contact the reproductive parts of the flowers on about half of their visits to the flowers. They sip nectar from the side of the flower instead.
On the other hand, our lovely solitary mining bees make no honey and they collect both pollen and nectar on every visit, meaning that each time they visit a flower they are contacting the reproductive parts of the flower. This makes them much more effective at transferring pollen and much more efficient as pollinators.
It’s clear that Trinity’s Campus Pollinator Plan is having some real results and it’s great to see the university protecting these incredibly important (and beautiful) pollinators!
By Dr Laura Russo, Marie Skłodowska-Curie Post-doctoral Fellow in Botany‘s Plant-Animal Interactions Research Group in Trinity‘s School of Natural Sciences.