How does Imidacloprid work?
Imidacloprid works by disrupting inhibiting stimuli transmission within the nervous system of a given insect when that insect either ingests or absorbs the poison into its body.  More specifically, imidacloprid blocks a certain type of neuronal pathways which are much more prevalent in insects than mammals. That is why the chemical is much more toxic to insects than humans or animals.

Products and Target Pests
Among the more well-known products containing imidicloprid are Dominion 2L Termiticide Concentrate, Maxforce fly baits, Merit Granules, Premise 2 Termiticide, and Pre-Empt Roach Bait Gel.  Target pests include a very broad spectrum of flying and crawling pests such as flies, termites, cockroaches, carpenter ants, and ground and ornamental pests.

Toxicity
The EPA gives Imidacloprid a class II or class III rating, meaning that is is "moderately toxic" and requires a Warning label.  It has been termed a “potential” pollutant of ground water.   Always follow the label directions.