WordNet sense 1 (a group of many insects):

swarm

WordNet sense 2 (make overcast or cloudy):

overcast

WordNet sense 3 (make less visible or unclear):

becloud, befog, fog, mist, obscure, obnubilate, haze over

WordNet sense 4 (place under suspicion or cast doubt upon):

corrupt, defile, sully, taint, defile

WordNet sense 5 (colour with streaks or blotches of different shades):

dapple, mottle