The Following Message Has Been Approved By The Kirkton Horticultural Society
Justin Toews sent this picture to me wondering what had left this tangled mess on his soybean leaf. I suspect others have asked the same question this year walking their soybeans and finding this symptom. You will see it on random, widely scattered plants. The chewing is confined to one or two leaves and doesn't spread to other leaves or plants.
It is caused by the thistle caterpillar which during the process of building his home leaves a tangled web and chewed up leaf. It takes him about a week to do his business and then he pupates. This is when the Horticultural Society gets excited.
The adult of the thistle caterpillar is the painted lady butterfly. Flower lovers adore butterflies. A few mangled soybean leaves are a small price to pay in order to keep the Horticultural Society happy.