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Megachilidae

Cosmopolitan family of bees

  • 6 min read
  • 3 chapters

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Lifecycle

Nonparasites

Nonparasitic Megachilidae typically divide their nests into cells. Each cell receives a supply of food (pollen or a pollen/nectar mix) and an egg; after finding a suitable spot (often near where she emerged), a female starts building a first cell, stocks it, and oviposits. She builds a wall that separates the completed cell from the next one. The larva hatches from the egg and consumes the food supply. After moulting a few times, it spins a cocoon and pupates. It emerges from the nest as an adult. Males die shortly after mating, but females survive for another few weeks, during which they build new nests.

Nests are often built in natural or artificial cavities. Some embed individual cells in a mass of clay or resin attached to a wall, rock surface, or plant stem. Nest cavities are often linear, for example in hollow plant stems (snail shells are used by some Osmia, and some species readily use irregular cavities).

Pollen collection by tapping has been observed only in the Megachilidae. Only the females possess an abdominal scope, which they use to gather pollen by holding the abdomen horizontally over the anthers, repeatedly lifting and lowering it against the pollen source, packing the dry pollen between the dense bristles of the scope. Their legs may assist in packing the pollen. During this time the female may also collect nectar, storing it in their crop.

Parasites

Some genera of megachilids are brood parasites, so have no ventral scopa (e.g. Stelis and Coelioxys). They often parasitize related taxa. They typically enter the nest before it is sealed and lay their eggs in a cell. After hatching, the parasite larva kills the host larva, unless the female parasite has already done so, and then consumes the provisions. Parasitic species are of equal size or smaller than their victims. In 1921, the journal American Museum Novitates published a preliminary report on parasitic megachilid bees of the western United States.

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