On a recent suburban safari to the wilds of Woodend Sanctuary in Chevy Chase Maryland, we met the interesting false milkweed bug foraging on beautiful oxeye blossoms. On a nearby roadway, dozens of rather large bees darted about a wooden guardrail. Beneath the cross members of the rail were several large holes, clearly the handiwork of carpenter bees like those we met in a previous episode. Upon closer inspection, the acrobatic bees performing nearby turned out not to be carpenter bees. No, these rascals were giant resin bees, exotic colonists from Asia first reported in the United States in North Carolina in 1994. In addition to their native Asian range that includes China, Japan, and South Korea, giant resin bees have been discovered in Italy and Switzerland in Europe. In North America they range from Canada to Alabama and have been reported in Maryland in nearby Prince George’s and Kent counties.
Giant resin bees belong to a family of solitary bees known as Megachilidae and are kin to mason bees and leaf cutter bees we met in previous episodes. Like mason bees, each female bee is reproductively active and therefore dissimilar to social bees like honey bees and bumble bees that have a queen. Their presence near a beam riddled with carpenter bee galleries is no mystery. Despite sporting powerful jaws, the potency of which I discovered after handling one, giant resin bees do not excavate galleries in wood. Their sharp jaws are simply not strong enough to do so. Instead, they rely on existing galleries to create a home for their brood. At Woodend, abandoned galleries of carpenter bees provided perfect chambers to colonize and raise their young. While male giant resin bees spend their time defending territories and chasing each other about, female bees gather plant resins to line the inside of the gallery. After each chamber is properly prepared, females collect pollen on fine hairs called scopa on the undersides of their abdomens, return to their galleries, and create pollen balls inside. Eggs are laid on the pollen balls, which serve as the food source for the developing larvae.
When not performing aerial antics, male giant resin bees can be found fanning their wings around co-opted carpenter bee galleries now occupied by female resin bees. Is he awaiting the appearance of a lovely lady while shooing away other bees?
The ecological impact of these nonnative bees is still largely unknown. They have been observed foraging on several imported plants from their native range including golden rain tree, Koelreuteria paniculata, glossy privet, Ligustrum lucidum, kudzu, Pueraria lobata, and Japanese pagoda tree, Sophora japonica. There is some concern that they may commandeer nesting sites of our native carpenter bees, but the true magnitude of this effect is still unknown. With the abundance of human made habitat for carpenter bees, there may be enough wood to go around for all wood-nesting bees. Who knows? Nonetheless, these goliaths of the solitary bee world are here to stay and they make an interesting study on a warm summer’s day.
We thank Woodend Sanctuary, Ann, Richard, and friends for providing inspiration for this episode. The interesting article “Invasive Megachile sculpturalis in Upstate New York’, by Robert G. Laport and Robert L. Minckley, was consulted in preparation of this episode. Bee guru Sam Droege, USGS Patuxent Wildlife Research Center, provided the fantastic image of a female giant resin bee featured in this episode.