Uncommon Oak Defoliator in Warren County

While doing some work in front of my barn I noticed small caterpillars falling onto my project from an overhead chestnut oak. I didn’t recognize what type of insect they were, but since they didn’t appear to be causing too much damage to the tree, I went back to my work and forgot about them. Then later that same day, I headed back into my woodlot to check on something and noticed that quite a few of my white and chestnut oaks were almost completely defoliated.

 My first thought was gypsy moth, but I also noted that the red and black oaks appeared untouched, which didn’t seem to make sense. I looked around for a while and could find no evidence of gypsy moth. After returning to the house, I gathered a few of the caterpillars and started looking for them in reference materials – then on the internet. It turns out that the caterpillars damaging my white oaks are a relatively little known species native to the eastern half of the country from Ontario to Georgia, called the Black–dotted Brown Moth Cissusa spadix. This particular caterpillar is relatively unknown because it is almost never considered a pest. However, according to articles on the internet, there has been an unexplained population explosion of the insect in several southern states, which occurred last month. Given the seasonal difference between here and Georgia, an outbreak occurring in New Jersey a month later makes sense. It might be good for landowners to be aware that oak defoliations this year may be caused by something else in addition to Gypsy Moth.