Last week, my lab crew found a few different caterpillars feeding in our soybean plots at the ISU Northwest Research Farm. They were hesitant to identify it in the field, so they brought one to me for a confirmation. First, I noticed it had a green body and green head and four pairs of prolegs on the abdomen. It is common to see green caterpillars in soybean (e.g., green cloverworm, soybean looper), but most don’t have four pairs of prolegs like this specimen.
Upon closer inspection, the body seemed velvety and covered with black hairs. Most caterpillars I see have a smooth body or have relatively few hairs. The final clue was the two, thick, white stripes along each side of the body. The lines had blobs of orange and pink. It had to be alfalfa caterpillar! Most of you are familiar with the adult of this species – a white or yellow butterfly.
Two adult color forms of the alfalfa caterpillar.
Photos by Charles and John Bryson, www.ipmimages.org.