The answer once again is its small size. An itch is in fact how our brains recognize small skin pain. The skin response is pain, but the lack of size sends the signal to the brain and instead of perceiving it as pain, we perceive it as an itch. Ask anyone who has been in the outdoors camping and they'll take a dozen mosquito bites over a single chigger bite any day. The best medicine here is prevention.
Chiggers are common to the southern United States.
They are found in brush and grass and cling to the vegetation waiting for a victim to walk by. Once they jump on their victim they burrow seeking out warm moist areas to feed. Bites will be clustered around pant legs and any place where clothing is restrictive. To avoid being bit, it is best to lightly spray the target areas as well as your clothing with a bug spray that states it is effective against chiggers. Wear light clothing as they seem to be more attracted to dark clothing and also you can spot them on lighter clothes.