The spot where they attach and insert their sucker thing is coated with a substance from them that keeps the opening open and allows the digested tissue to flow. That substance is what causes the itch. The chigger itself falls off, just like a tick, after sucking your flesh. Poor choice of terms.
A good source on chiggers at this link from Missouri;
http://mdc.mo.gov/nathis/arthopo/chiggers/
We need a chigger smiley....
A good source on chiggers at this link from Missouri;
http://mdc.mo.gov/nathis/arthopo/chiggers/
We need a chigger smiley....