As an Extension professional, I am on the receiving end of a lot of questions, just like my colleagues across the state. These questions come in the form of telephone calls, emails, text messages, photographs, personal conversations and actual samples. Sometimes these questions are answered easily with a quick reply. Sometimes the question needs additional information, photo documentation, more researching, or should be sent on to the OSU Plant and Pest Diagnostic Clinic (https://ppdc.osu.edu/).
Earlier this week an Ask An Expert question came through with a pretty good photo to aid in its swift identification (see photo below). The person was at a park, and happened to come across this insect that they were unfamilar with. They included some basic information about where they were at when they saw the insect, and confirmed the timing (it was earlier in the week, and not three months ago as timing can be important). Something that I always suggest when taking a photo is to include something for scale - maybe a quarter, ruler, pencil - something universal in size so we don't have to guess - ie., someone's hand or shoe, or another object that could be found in a variety of sizes.
The insect in question was IDed as the zebra caterpillar (Melanchra picta (Harris)). While I was not familiar with the caterpillar personally, it had some distinguishing characteristics that made it fairly easy to confirm. Colorado State University has a publication, Caterpillars on Field Crops, that describes the caterpillars as an insect easily distinguished from other crop caterpillars by two bright yellow stripes running along each side of the body and separated by alternating black and white stripes running around the body. This insect can be found defoliating a variety of broadleaf field and vegetable crops, ornamental trees and flowers. It is generally not considered to be a serious pest. Damage from these insects can be expected in late May and June and again in late August and September. The caterpillar can be up to 1 1/2 inches in length.
Dr. Dave Shetlar mentioned from his own experience, the zebra caterpillar is a pretty common pest of cole crops. Maybe a fan favorite! With that said, the critter does has a pretty wide host range and being a rather spectacular caterpillar that is easily noticed, it may leave people wondering - what is it? The University of Minnesota Extension describes the host range to include cabbage as well as broccoli, asparagus, spinach, potato, and tomato. It also attacks flowers, such as aster and hydrangea.
Joe Boggs first encounter with this critter was in the former Rose Garden at Secrest Arboretum where the caterpillars were feeding heavily on the roses. At first glance, he thought they were sawfly larvae because of their general shape and genuine appreciation of the roses, but the prolegs just didn't add up. Remember - caterpillars have five or fewer pairs of prolegs with hooks at the base of the prolegs called crochets, where as sawflies have six or more pairs of prolegs and no crochets.
The caterpillars are gregarious leaf skeletonizers in their early stages, but they become solitary as they get older and can be observed feeding individually. When the caterpillars are alarmed, they roll up into a ball and drop off the leaf.
The adult moths have a long flight period, so both adults and caterpillars can be found throughout the summer and into fall. As the fall season winds down, the caterpillars pupate and overwinter in the soil. They will emerge the following season as adult moths. Below are a couple photos of these stages of development.
So when you are out and about in your garden or landscape, or maybe even visiting a local park, garden or arboretum, while you won't come across an actual zebra, you may just happen to see a zebra caterpillar. Let the searching begin!