A lek is a gathering of male animals where the males parade around, showing off their best features to their female admirers. By marking her score card, a female can then select the best father for her offspring. Leks occur just before and during breeding season, and may attract participants from great distances.
According to Wikipedia, leks are of two types: classical and exploded. In a classical lek, the males are in sight of each other and they may engage in physical contests. In an exploded lek, the animals are further apart and use vocal signals to spar with each other. Lekking behavior occurs in some species of birds, fish, bats, and insects.
Last August, I had been watching the goldenrod every day, photographing an assortment of pollinators. Then one day, I discovered the plant was covered with hundreds of tiny black bees. After capturing a few in a net, I made my best guess: I thought they were some kind of sweat bee, probably in the genus Lasioglossum (Halictidae). Good enough, but I couldn’t figure out why so many bees were so close together. When I tried to get near, they all flew aloft, but they reappeared as soon as I stepped away. It didn’t look like any foraging expedition I had ever seen.
So I asked Eric Eaton (Bug Eric) if he knew anything about this strange behavior and he clued me into lekking. And sure enough, Lasioglossum is one of a few genera that includes species with lekking-based mating systems. Like many other bee species, these tiny sweat bees also exhibit protandry, which mean the males are born first so they can mature and be in place by the time the females show up to make their selection.
These bees didn’t let me anywhere near, so the photos are iffy. But if you use your imagination, you can see all the males staking out their territory on the only goldenrod plant in the area. Click to enlarge.