Megachile mellitarsis
(By K. James Hung)
Despite the general drought conditions that continue to persist in San Diego’s ecosystems, there were still pockets of time and space this year where rainfall was sufficient to support excellent plant and pollinator communities. Earlier this spring, parts of the Anza-Borrego desert got some of the best rains in the last few years. Because of these rains, we were able to find some pygmy cedar in bloom! Contrary to its name (and appearance), the pygmy cedar is not a cedar—it is a unique plant in the sunflower family (Asteraceae), in a genus of its own: Peucephyllum schottii. And on this remarkable plant, we found some Megachile mellitarsis!
To our knowledge, the bee photographed above represents the first record of this species in San Diego County. Like almost all other members of the family Megachilidae (leafcutter, wool-carder, and mason bees), the female collects pollen not on her legs, but rather on a pollen brush on the underside of her abdomen. One can see that this female is quite productive; she has pollen overflowing even onto the top side of her abdomen!
Little appears known about the natural history of this leafcutter bee, though it can be readily identified by its orange tarsi (“feet”) from which it gets its scientific name (visible in the photo above). While this species is not restricted to foraging on pygmy cedar, available records indicate that it does generally favor plants in the sunflower family. It is interesting to see that this bee has chosen pygmy cedar as its host of choice here, given how rare pygmy cedars are in the area and the fact that the bee occurs in many areas that completely lack pygmy cedars. Perhaps pygmy cedar nectar is especially tasty? We only saw about 15 of them in bloom the whole day, and 100% of the M. mellitarsis we saw were on one of those 15 plants.
Megachile mellitarsis Cresson, 1878
Family: Megachilidae
Tribe: Megachilini
Active season: Depends on locality; mostly March through June
Range: Northwestern Mexico, western North America
Floral preferences: Appears to favor sunflower family, but may accept other flowers
Nesting biology: Unknown, though close relatives build solitary nests in pre-existing wood cavities using chewed leaves and mud.