The tailed Whipscorpions belong to the Order Uropygi which contains around 85 species worldwide. Only a few species are found in the United States, the largest being the giant Vinegaroons, Mastigoproctus giganteus, found in the Southwestern states.
The key identifying character is the long, thread-like segmented tail extending from the end of the abdomen. This tail is INCAPABLE OF STINGING (OR BITE, or anything by the way) , but the giant Vinegaroons aims a vinegar-scented mist from a gland at the base of its abdomen when disturbed. The spray contains acetic acid and another substance that attacks the exoskeleton of other arthropods.
Vinegaroons ARE BENEFICIAL creatures and should be left undisturbed when found. Should one enter a structure, it should be captured and released outside.