Approaching destructive swarms of insects can often be forewarned by distinct morphological variations of individuals, be they solitary or gregarious. E.g. solitary female locusts have a pronounced pronotal crest relative to gregarious (the swarming type).
Individuals with knowledge of the pest group (animal skill) can predict the coming of a plague, swarm, etc.
Swarms are one of the things that can happen to a community. See Stochastic Disasters. The level of stochastic disasters can be set as a community variable.