This mesmerizing photo, shot by iNaturalist member “Stonebird,” is the best depiction of a mating lek I have ever seen. It is so dense with bees, it almost looks like a honey bee swarm. I cropped the photo a bit so you can see the details, but the branch holds many more of these striking creatures.
On iNaturalist, the description reads, “Agapostemon melliventris sweat bees gathering on goldenrain tree flowers along Ballona Creek at the end of the day.” The goldenrain tree, Koelreuteria paniculata, was introduce into the US back in 1763. It is a popular landscape species that is also known as China tree, varnish tree, and pride of India. Ballona Creek is a nearly nine-mile-long waterway in southwestern Los Angeles County.
What is a lek?
A lek is an accumulation of male animals that forms during mating season. Wikipedia describes it well: “A lek, from the Swedish word for “play”, is an aggregation of male animals gathered to engage in competitive displays, called lekking, to entice visiting females which are surveying prospective partners for copulation. Leks are commonly formed before or during the breeding season.”
In many ways, a lek is like a drone congregation area except that a drone congregation area forms in mid-air. A lek is usually in or near flowers. In some species, the females fly over the lek to look for a suitable mate, just like a honey bee queen flies over a drone congregation area.
A popular spot
This photo was taken in October, just at the height of the season for these bees. Stonebird wrote, “On the goldenrain tree I observed that the sweat bees were gathering on the very same small cluster of leaves for over a week toward the evenings.” That sounds exactly right. The males of many species often go back to the very same spot to spend their evenings.
Bees may find the right spot by detecting pheromones that remain from the previous day. In fact, pheromones are the reason a honey bee swarm may cluster in a spot that was previously used by a different swarm. Days, weeks, or even months may pass before the next swarm arrives.
On the other hand, something else could signal the spot. Honey bee drone congregation areas also occur in the same spot year after year. Since no drones live from season to season, there are no individuals that can pass on the information. Why or how they select the same spot every year remains a mystery.
A honey of a bee
The common name for these bees, the honey-tailed striped sweat bee, better describes the female than the male. As you can see, the male abdomen is striped with yellow and black. The female abdomen is often a golden honey color between light-colored stripes that are nearly white. Although their abdomens look very different, both sexes have a metallic green head and thorax.
Like other sweat bees, Agapostemon are solitary bees that nest in the ground. Most often, the nests are scattered randomly, so they are hard to find. Sometimes, however, they will nest close to each other, and occasionally females will share a nest entrance. Nevertheless, each female maintains her own separate nest within the burrow and cares for her own young.
A southwestern species
Although the genus Agapostemon is widely distributed across North America, this particular species is only found in the southwest from Texas to California, and south into northern Mexico. Lately, though, sightings as far north as Oregon indicate their range is expanding.
Oddly enough, as I was writing this, a random reader of this site sent me a photo of a female Agapostemon melliventris, and asked “What bee is this?” My guess is they are fairly common and, because they are so beautiful, people notice them.
Honey Bee Suite
Please Note: You can see many more photos by Stonebird at iNaturalist.org.