The spiny tachina fly is yellow-orange with heavy black bristles and rather large at about ½ – ¾ inch in length. The distinctive bristly body of these flies has led to them being commonly referred to as “hedgehog flies.” The advantage derived from the presence of the thick bristles is not known. The antennae have three segments, with a large lobe at the end. As with all flies, spiny tachinas have a single pair of wings attached to the thorax or mid section of the body. In place of a second pair of wings is a pair of rod-like balancing structures called “halteres,” which are found behind the wings on the aft portion of the thorax.
Larvae of this fly and others in the family Tachinidae tend to be parasitoids, meaning that they feed on the host and ultimately kill it. Most are generalists in the choice of hosts, the eggs being deposited by adult females onto the bodies of other insects, such as caterpillars of butterflies and moths, beetle larvae, grasshoppers, and larvae of other flies. Eggs hatch quickly and the larvae burrow into the tissues of the host insect, where they feed on the tissues of the host. Other tachina species lay eggs on leaves or in the burrows of hosts, depending upon the host passing by and coming into contact with the larva which is searching for the host. Some tachina species are merely parasites, living off the tissues of the host but not killing it.
Adults feed on nectar from late summer flowers and pollen and are not parasitic. Thus the species is termed “protelean” which refers to animals that are parasitic or parasitoids during the larval stage but free living as adults. Flies may overwinter by taking refuge in leaf litter or pupate and stay inside the bodies of hosts until the following spring.
In their ecological role wherein they prey on and diminish or destroy other insect pests, such as gypsy moths, cutworms, squash bugs and others, tachina flies can be agents of biological control on pest species and thus beneficial to agriculture crops and to vegetable gardens. They also function as pollinators of the flowers they visit, complementing the actions of bees and hummingbirds.