Natural History

The Spiny Tachina Fly is a member of the Tachinidae Family. They are large flies, growing to 1/2 - 3/4 inches in length and have black and yellow or brown bodies which are covered with bristly hairs. Spiny Tachina Flies occupy foothill and mountain habitats. Adults are active from late summer through early fall and are usually found sucking nectar on plants in the aster family, especially rabbitbrush and coyote brush.
 

Females lay a small whitish egg upon the skin of a caterpillar. This egg is glued tightly and is large enough to be readily seen by the unaided eye. When the larva fly hatches it eats its way through the egg and into the caterpillar's skin living inside of the body of it's host which it usually kills. When the larva becomes full grown its skin hardens into a brown pupa case within which it changes into a pupa. A little later the pupa changes to a Tachina fly which breaks apart the pupa case and flies out into the world.