Cooperative
Extension
Service


University of Illinois
at
Urbana-Champaign


No. 6/May 1, 1998

Finding Pests That Aren't Pests

By the time you receive this issue of the Bulletin, May will be upon us. Unfortunately, a lot of growers, retailers, and applicators are frustrated by the delay in corn planting caused by the persistent wet weather. Nevertheless, some folks are keeping busy by watching for critters in the few fields that have been planted, and sometimes by foraging through fields that have yet to be planted. Consequently, people will find the occasional "worm" or "bug" that looks like it might cause a problem, but then again, maybe it won't. As a result, we receive occasional telephone calls that test our ability to identify organisms based upon the callers' sometimes unique and usually creative descriptions of the creatures lying on the desk in front of them. More patient observers send us specimens so that we can view the offenders up close and personal. (Please note that we prefer the latter approach. We have a miserable track record of identifying insects over the phone.)

I recently received a small bottle filled with soil in which the senders had placed a few small, wormlike creatures that resembled third-instar cutworms. They were dark brown to black, about 1/4-inch long, and in addition, the animals were curled head to tail, very much resembling cutworms at rest in the soil. Based upon their general appearance, the insects might easily have been mistaken for black cutworms. However, when I looked at them under the microscope, I learned that the "bugs" I had under the spotlight were not black cutworms--they were crane fly larvae.

Crane fly larvae are not pests of corn. They are found occasionally in the spring during or shortly after corn planting and are often mistaken for cutworms. However, the absence of both true legs and prolegs distinguishes crane fly larvae from cutworms. In addition, a crane fly larva's head is narrow and often retracted into the segments of the thorax. The last abdominal segment has two dark, circular spiracles, or breathing pores, and may have fleshy projections. (The specimens sent to me from McDonough County had fleshy projections on the last abdominal segment.) The larvae usually occur in damp situations where decaying plant material is abundant. A typical crane fly larva is depicted in Figure 1.

Figure 1. Crane fly larva.

Because crane flies do not injure corn, insecticides are not necessary for their control. Don't make the mistake of applying an insecticide to control a "pest" that's not a pest. Rely upon your diagnostic skills before you make a hasty decision, and if you are in doubt, send the specimens to us. We'll do our best to answer your questions quickly.

Kevin Steffey (ksteffey@uiuc.edu), Extension Entomology, (217)333-6652