(A closer look with Gwen …)
This spring my friend Carl invited me to visit a site in Brackendale where many bees were active on warm days. The site is a field that until recently was mowed and is now being left to naturalize for the benefit of pollinators, birds, and other small critters.
My first impression was of small mounds of dried grasses and areas of bristly moss and sandy soil. Then I realized that there were hundreds of bees crawling on the ground or circling a few inches above the ground. This wasn’t feeding behaviour as there were only a few flowers in sight so I guessed that we were witnessing nesting behaviour. There were some holes visible in the sandy areas and this made it possible to photograph the bees but the areas with dried grasses seemed to be preferred for providing better cover for the nest entrances. We also saw mating behaviour, with many males competing for access to a single much larger female.
As I expected for this setting and time of year, we saw at least two species of Andrena (mining bees). The genus includes many species in BC and only a few can be identified in the field or from photos. All Andrena dig nest tunnels straight down, from 15 cm to more than a metre deep. They line the tunnels with a waterproof substance to protect the eggs and young from moisture and soil bacteria.
In addition to Andrena, we saw Nomada (nomad bees) who are cleptoparasitic, mostly on Andrena: they secretly invade host nests and lay their eggs there. An Andrena female creates a cell in a nest tunnel, lays an egg, provisions it with pollen and then leaves the nest to repeat the process. In the meantime, a Nomada female can take the opportunity to enter and lay an egg in the wall of the cell. This can happen up to four times in one cell. The parasite’s larva that hatches earliest eats its “siblings”, then the Andrena egg, and then the pollen intended for the Andrena. The survivor Nomada emerges next spring.
Carl reported that in the mornings he saw the Andrena tentatively using their antennae to check the temperature outside their nests to determine whether it was warm enough to emerge for the day. Unlike bumblebees, these species are not able to warm themselves so when it is cool they need the sun to warm their body temperatures to 10 to 16 °C before they can fly.
Many municipalities now recognize that leaving boulevards and similar areas un-mowed benefits pollinators and birds. Although this practice is not popular with some citizens because the areas appear unkempt, many understand that the benefits outweigh the disadvantages. Leaving insects and plants to complete their life cycles provides habitat and food for many species, including ground-nesting and migrating birds. This is all about conserving and promoting biodiversity. Please think about what you can do to help (and then do it!).
Information and photos shared by an interested amateur ….