It's often very difficult to identify insect larvae in the field, especially when they're covered with mud. Unfortunately, one of these larvae, the crane fly, which is not a pest of corn, is often confused with the black cutworm. Crane fly larvae, also known as "leatherjackets," are occasionally found in the spring in crop fields and pastures. Ron Hines, senior research specialist at the University of Illinois Dixon Springs Agricultural Center, found one of these creatures as he dug in their wireworm bait traps in Pope and Massac counties the first week in April. Crane fly larvae are found along or just below the soil surface. They prefer moist conditions, such as poorly drained fields, and feed on decaying matter, fungi, and moss.
Crane fly larva found in a wireworm bait trap. (Photo courtesy of Ron Hines, Dixon Springs Agricultural Center.)
Illustration of crane fly larva showing the absence of legs and the presence of fleshy protuberances on the anal segment.
Black cutworm larva and cut corn seedling.
Approximately the same color and size of a fourth-instar black cutworm, crane fly larvae are dark colored, with poorly developed heads and fleshy projections around the tail end of the body. The distinct difference between crane fly and black cutworm larvae is the legs. Crane fly larvae are legless, whereas a black cutworm larva has three pairs of true legs on the thorax behind the head and fleshy prolegs on the abdominal segments. Black cutworm larvae also have a well-developed head and no tail-end projections. Once again, it's important to remember that correct identification of insects and accurate diagnosis of potential insect problems save time and money in the long run.--Kelly Cook