The ceanothus are in full bloom in several areas of the park. They look blue to our eyes; some are shaded toward purple. The Black-tailed Bumblebee (Bombus melanopygus) can see blue and purple very well, and can probably also see dots of ultraviolet where the flower holds the sweet nectar. Notice how fast this bee is working the flowers. The ceanothus bush offers a lot of nectar but all in tiny doses, so that you have to work for it. That’s not a big problem for the bumblebee. Bees generally can distinguish shapes with colors much more quickly than human eyes can. To us, the tiny blue flowers seem to go by in a blur, but to the bee, each one is sharp and clear.
Oddly, bees can’t see red. They can make out reds mixed with yellow, but not pure red. Their eyes don’t have rods for red. In exchange, they can see ultraviolet, including blues and purples mixed with ultraviolet that human eyes can’t make out at all.
Both the ceanothus and this bumblebee are long-time inhabitants of California, present before the first Europeans landed here and brought over bugs, plants and other life forms from the Old World. The Black-tailed Bumblebee, in particular, is a resilient survivor, being the only bumblebee to still inhabit San Francisco. They nest in the ground or, alternatively, high up in tree cavities or in unused birds’ nests. The bee in the video is probably a female and very likely a queen. It mated last fall and spent the winter alone in a solitary nest. Now it goes around gathering pollen and nectar to provision a new nest where it will build up a food store for the eggs it will lay, to feed the larvae that hatch from the eggs. This will produce some workers who will then help the queen to gather even more food to feed even more larvae. At some point the queen will remain in the nest dedicated entirely to brood production while all those workers do the foraging and feeding of the brood. Eventually, new queens and males are also produced which will mate. The workers and males die off come winter. Each queen will spend the winter alone in its own chosen site until early spring, when the cycle starts anew.
This ceanothus, by the way, is one of the native bushes planted by the DAWN project in the early 1980s.
Thanks to Jutta Burger for the bee ID. Thanks to Peter Rauch for background on bee reproduction.