As of spring 2022, Rachel Fordyce is employed as a laboratory technician in the Department of Entomology (the branch of zoology that studies insects) at Cornell University in New York State. Every morning, on her way to her workplace, she passes a large cemetery in the municipality of Ithaca and quickly notices a “abnormal presence of insects”reports Wired. The young woman then spoke about it to one of her colleagues, Bryan Danforth, an entomologist.
After collecting a few specimens, their analysis revealed that it was a colony ofAndrena regularisalso called “sand bee”. In this species, which has so far been little studied, the female digs nests in the ground and deposits her eggs in incubation cells containing pollen and nectar. When the eggs hatch, the larvae continue to develop underground. They overwinter, and end up coming out into the open air when the apple trees bloom in spring.
By pushing their investigations further, the scientists discovered historical archives revealing the presence of this insect in the cemetery since the beginning of the 20th century. They then launched a vast inventory of bees and quickly realized that they had discovered one of the largest concentrations in the world. The results of this study are published in the journal Apidologie.
An underground megacolony
To identify these foragers, the research team installed ten traps in the 5,000 m cemetery.2. These nets, covering a square meter of soil, redirected the bees emerging from the ground towards a glass container, to be counted. According to researchers’ estimates, this impressive colony brings together between 3 and 8 million individuals, for an average of around 5.5 million bees, the equivalent of more than 200 hives of domestic bees.
This discovery made it possible to learn more about the biology of this bee. In particular, we observed that the males emerged from the ground a few days before the females from the first warm weather in April, in order to optimize their chances of reproduction. Scientists have also highlighted the complex relationships that structure this population: among them, parasitism exerted by another bee, Nomada imbricata, a bee strangely resembling a wasp, which lays its eggs in its host’s nests, to the detriment of its offspring.
This study highlights the importance of preserving wild bee nesting sites. Old urban cemeteries (this one dating from 1878), with their sandy soils and low exposure to pesticides, constitute particularly favorable refuges.
Fearing that entire colonies could disappear due to development work or urbanization, researchers launched a citizen science program. The objective is to invite the public to report underground bee colonies in order to better identify and protect them before the fragmentation of their habitat threatens their survival.
