You may have recently read about our new pig, Miss Piggy; she just moved in with our older pig, Squealer. Pig introductions don’t usually happen without at least some scuffling to establish dominance. During the introduction, both pigs displayed quite a bit of piloerection, or raised hairs.
The word piloerection comes from the Latin root pilus, which means hair. Piloerection occurs in many mammals and happens when the tiny muscles at the base of each hair follicle contract. Piloerection can happen in response to cold and the raising of the hair helps insulated the skin. In humans, this process produces “goose bumps”.
In many mammals, the response has been co-opted by natural selection to serve as a signaling mechanism. The raised neck hairs (or “hackles”) on our pigs were not a response to cold but rather a signal to the each other of heightened awareness and the threat of aggression. Our pigs are getting to know one another and we aren’t seeing much piloerection now.