Thick-headed fly, Conopidae (probably Zodion sp.) attacking Leafcutter bee, Lithurgus sp., on flower of Engelmann's prickly pear, Opuntia phaeacantha discata. Female Conopid flies wait in ambush for bees, then dart out and quickly thrust an egg through the membrane between the abdominal plates of the bee. The fly larva develops inside the abdomen of the host bee, eventually consuming its internal tissues. Saguaro National Park, Arizona
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