Self Service (1974)

Hungry mosquitos, in search of a meal, find that fruit, flowers and other such fare doesn't satisfy. One enterprising bug hits the jackpot - a human! However, the victim vigorously resists joining the food chain, causing a number of winged casualties. The little buggers wait until the man falls asleep, then set up a number of enterprises: cafes, bars, filling stations, all serving blood. Things are going well, but then the mosquito Cosa Nostra moves in, and ramp production into high gear.