Ectoparasite

Ordinarily, allergy to animals is due to either their fine dander which becomes aerosolized or to the exoskeleta, pupae, or feces of their ectoparasites.

Many of the chewing lice are highly host specific, but a few may occur on a variety of not more than a half dozen related host species. They feed on skin (epidermal cells), hair, feathers, body oils and secretions, dried blood (wounds), and even other ectoparasites, such as mites. Chewing lice are unable to survive for more than a day or two off the host and their dispersal is through direct contact of host animals.

I was so thrilled to see a live bedbug, I showed it off to every graduate student I ran into that day: Cimex lectularius[,] a small, flat, wingless, brown ectoparasite that hides in cracks and crevices in human dwellings and emerges under cover of darkness to feast on human blood. […] Bedbugs win neither praise for their sophisticated technique, nor very much respect for the fact that they don’t carry diseases, as most bloodsucking human ectoparasites do.