Image Credit: Ian Jacobs
Micro-Carpenter Bees (Anthophoridae: Ceratina)
Ceratina are small to tiny bees, immediately recognized by their metallic iridescence (weak in the commonest species) and facial markings. They are probably the commonest nest builders in the pith of broken plant stems. They seem to actively remove the old pith of blackberry (Rubus), butterfly-bush (Buddleja) and snowberry (Symphoricarpos) bushes in the Willamette Valley. The male and the female have contrasting markings on their upper lips.
The pollen-transport scopa on the hind leg is surprisingly small, even though one might expect it to be relatively small since they live in unforgiving narrow chambers. However, it raises the possibility that they might supplement the pollen load with swallowed pollen (like the Hylaeus bees do). Nests are apparently extremely simple – just the hollowed-out pith with no elaborations and a very wimpy effort at doors to separate cells in the series. Reproduction is usually the typical form in solitary bees with fertilized eggs becoming female and unfertilized eggs becoming male. However, typical reproduction is supplemented by parthenogenesis (reproduction without mating or “cloning”) in certain populations of our commonest species, C. acantha. To the south, in California, an introduced species (C. dallatorreana is apparently completely parthenogenetic.
Ceratina in the PNW are often rather darkly colored, and without direct sunshine appear black (resembling Hylaeus or some of the smaller Megachilidae). They do not have fasciae which shouldn help discriminate them from the megachilids but they often have yellow spots on the thorax that will continue the confusion with Hylaeus. They probably have multiple generations per year in the Willamette Valley.