Chigger

A chigger is a small, parasitic mite which lives in tall grass. It is a member of a larger family known as the Trombiculidae. 
The species of Trombiculidae which bite in their larval stage cause "intense irritation", or "a wheal, usually with severe itching and dermatitis". 
Their color can range from bright red to brown. Chiggers are almost too small to see with the naked eye, so checking grass for them is near impossible. Chigger bites appear 2-3 hours after a host is bitten, and can last for a few weeks. They bite in hot, moist places, such as the armpits, under the knees, and the genitals.
Trombiculidae live in forests and grasslands and in low, damp areas such as woodlands, berry bushes, orchards, along lakes and streams. It does live in drier places, such as lawns, golf courses, and parks. They are most numerous in early summer when grass, weeds, and other vegetation are heaviest. 
In their larval stage they attach to various animals and feed on skin, often causing itching. 
The best known species of chigger in North America is the hard-biting "Trombicula alfreddugesi" of the southeastern United States, humid midwest and Mexico. In the UK, the most common chigger, the "harvest mite", is "Trombicula autumnalis". It lives through Western Europe to Eastern Asia.