By Linda Williams, DNR Forest Health Specialist, Woodruff
Linda.Williams@wisconsin.gov or 920-360-0665

Webbing and a collection of frass (caterpillar excrement) around these cones is the web nest of pine webworm. / Photo Credit: Wisconsin DNR

Pine webworm (Pococera robustella) is a native moth whose caterpillars feed on pine needles. In Wisconsin, the caterpillars prefer young jack pine and red pine. A single generation per year occurs in Wisconsin.

Young larvae mine needles, feeding within the needle. Older larvae form a compact web that they fill with small, oval pieces of frass. In early fall, the larvae drop to the ground to pupate and spend the winter.

Tearing open ta fall webworm nest reveals two pine webworm caterpillars within. / Photo Credit: Wisconsin DNR

Pine webworm adults are moths. This insect is different from pine false webworm, which is a sawfly.

Recently, a few of the web nests were observed in a young jack pine plantation in Oneida County.  Historically, in Wisconsin, this insect has only rarely caused small, localized outbreaks and does not result in notable mortality of young trees. Small outbreaks occurred primarily in central Wisconsin from 1958 to 1961, and again in 1979 (Grant County) and 1991 (Adams County).

Management is mostly natural, with eight parasites and several predators (including birds) that attack or eat the larvae and keep them in check.