Southern Carpenter Bee

Appearance

"X. micans" is a large carpenter bee, ranging between 15 and 19 mm long and 8 and 9.5 mm wide. The body of the bee is generally a metallic black and reflects light with blue or green tinges. The bees have a flat clypeus and relatively short mandibles in addition to a set of lateral ocelli set below the top of the head. Both males and females have short, dense pubescence on the head. Although the males and females of "X. micans" are largely monomorphic, they differ in the amount of hair covering their bodies. Females have sparse, dark pubescence on the scutum and scutellum, whereas males have scutum and scutellum that are densely, pubescent with bright-yellow coloring. Furthermore, whereas females have bare terga 1–4 and white tufts of hair from term 5 and 6, males have all terga 1 and 2 covered in yellow pubescence, and terga 3–6 with black pubescence.

Like other "Xylocopa, X. micans" creates nests by excavating in woody plant material, such as the dead wood of nearly any species. However, the nests of "X. micans" have rarely been observed in nature. Females use strong jaws to vibrate holes in wood, and then burrow to form a nest of roughly 8 mm in diameter, with several brood cells spaced along the length of the nest. The entire length of the nest is roughly 12 cm.

Distribution

"X. micans" is found in several states in the southeastern United States, along the coast from southeastern Virginia to Florida, and west along the gulf to Texas. The bee can also be found further south in Mexico and as far south as Guatemala. The bee can be found only in the warmer months in certain regions such as the Lower Rio Grande Valley, but is generally found year-round elsewhere.

Specimens of "X. micans" have also been found moving as far north as Prairie County, Arkansas. The northward expansion may be reflective of range shifts of species predicted by climate change; similar impacts of climate change have been seen on the Edith's checkerspot butterfly. Conversely, since the specimens found in Arkansas were mainly co-located with Interstate 40, the range expansion could be caused by human activity; the southern carpenter bee could burrow into commercial lumber that could then be transported northward for several hundred miles.

Behavior

Southern carpenter bees are nectarivores. Males will forage from 12 PM until 4 PM at the latest during the summer months, although males with territories will forage for only one hour before returning to defend their territories. "X. micans" bees exhibit risk sensitive foraging, where bees demonstrate risk-aversion to completely empty flowers and favor flowers with nectar. "X. micans" is also polylectic, meaning that "X. micans" bees are general pollinators and can collect pollinators from a broad variety of plants. They also have special abilities for pollination, since they are capable of buzz pollination, a technique that allows the bees to dislodge tightly held pollen using resonant vibration. This ability expands the types of plants that "X. micans" is capable of foraging on.

Evolution

All carpenter bees of the genus "Xylocopa" are solitary and therefore generally do not form colonies. Both males and females of "X. micans" overwinters in old nests as adults until the following spring; each generation lives for roughly one year. In early April the adults emerge from their nests for the mating season.

Nests are preferably recycled by bees, who prefer to avoid the energy-intensive activity of excavating a new nest. When necessary, females will excavate nests by boring a hole into a piece of wood, making a sharp orthogonal turn, and boring down to form a tunnel with several brood cells, moving one inch every six days. Each brood cell is provisioned with a ball composed of pollen and regurgitated nectar. On top of the food ball, the female will lay an egg, and then plug up the respective brood cell with wood pulp. After filling each of the brood cells in this manner, the female dies.

Bees of "X. micans" develop from egg to adult over the course of seven weeks. New adults break out of the brood cell partitions several weeks after reaching adulthood, generally in late August, to collect pollen to store for overwintering. The bees quickly return to their nests to overwinter."X. micans" is a member of the subgenus "Schonnherria", which is largely neotropical"." "X. micans" likely became separated from a South American ancestor species during Pleistocene glacial maxima in Florida. In the current period between ice ages, it has moved back southwest toward Guatemala.

"X. micans" serves as a key example for step-wise evolution in the genus "Xylocopa". Many "Xylocopa" bees demonstrate resource defense polygyny, and many demonstrate lek polygyny. "X. micans" serves as a bridge between the two, exhibiting both states. It serves as an intermediate in terms of mesosomal gland size between those species requiring resource defense polygyny and those species requiring lek polygyny. "X. micans" also demonstrates that evolution of sexual dimorphism followed the evolution of non-resource defense mating strategies in "Xylocopa". Monomorphism is the ancestral state, and "X. micans", which shows both mating strategies, have males partially covered in light hairs, showing the beginnings of sexual dimorphism that grows more prominent in species that require lek polygyny.