I came across a small silk nest on pin oak (Quercus palustris) earlier this week in northern Kentucky which I first thought was the handiwork of Fall Webworm (Hyphantria cunea). Nests of this native web-spinning caterpillar are currently obvious throughout Greater Cincinnati and oaks are on their menu.
However, the nest seemed far too small for second-generation fall webworms at this time of the year. A close examination revealed several yellowish-brown caterpillars with dark brown stripes that I had never seen before.
Thanks to a new USDA Forest Service publication, I learned the web-nesting caterpillars are Striped Oak Webworms (Pococera expandens, family Pyralidae (Snout Moths)). They will eventually grow up to be the native Double-humped Pococera Moth.
The striped oak webworm nest was comprised of two distinct architectural designs. The cobweb-like outer structure involved green leaves loosely webbed together by random strands of silk. The leaves showed signs of caterpillar feeding damage.
Embedded within the outer silk framework was a dense, hardened structure composed of brown, dehydrated leaves tightly bound together with silk. This inner sanctum resembled the pupal hibernaculum produced by some silkworm caterpillars (family Saturniidae). In fact, as I tore apart the hard structure, I expected to find a big fat pupa residing in a hollow cavity.
Instead, I found dry, brown leaf debris tightly webbed together with dense silk that held large quantities of insect frass (excrement) pellets. Several silk-lined tunnels were hidden within this inner structure and striped oak webworms popped their heads out when I squeezed their silk frass-house.
The USDA Forest Service publication notes that little is known about the biology of the striped oak webworm. This implies it's not a serious oak pest. I've never seen this caterpillar before and only found one nest on a large pin oak surrounded by several other equal-aged pin oaks. Thus, striped oak webworms currently seem to be more of an oddity rather than an ongoing threat to oak trees.
However, I now wonder how many times I've walked past striped oak webworm nests thinking they were fall webworms; particularly if the nests were out-of-reach high in the tree canopy. Perhaps this native moth has been flying below our radar.
Helpful Caterpillar ID Publication
The USDA Forest Service publication titled, "Illustrated Guide to the Immature Lepidoptera on Oaks in Missouri" was published this past June by the Forest Health Assessment and Applied Sciences Team. Of course, "Immature Lepidoptera" means caterpillars.
This user-friendly publication includes a helpful table that guides you towards a successful caterpillar identification based on "Feeding Guilds" (e.g. "Leaf Miners," "Web or Tent Makers on Multiple Leaves," etc.). Informative descriptions of a vast array of caterpillars that feed on oaks are illustrated by outstanding pictures. Although the focus is on Missouri, our two states share many lepidopterans.
You can view this 368-page publication and download a PDF version by clicking on this hotlink: