What is "tachinidae"

The Tachinidae are a large and variable family of true flies within the insect order Diptera, with more than 8,200 known species and many more to be discovered. Over 1300 species have been described in North America alone. Insects in this family commonly are called tachina flies or simply tachinids. As far as is known, they all are Protelean parasitoids, or occasionally parasites, of arthropods.