Saturday, July 15, 2017

Innocent White Moth

Walking a trail on an overcast day I spotted a small white moth on a leaf.  After a quick photograph it started to drizzle and I clipped off the branch to inspect later.  The next morning the moth hadn't moved until I nudged it but it still hung on tight.  There was a fuzzy white patch on the underside of the leaf and a smaller one under the moth when I bent the leaf.  I could see a mass of eggs and surprisingly the moth didn't fly off.  After photographing it I kept it for a week with the now dead moth clinging to the leaf.

Eggs in underside of leaf

This is the Fall Webworm Moth, Hyphantria cunea.  WAIT!   Before you hit the delete remembering those hated masses of silk on your tree during their big year in 2016, follow along to know thine enemy.  After mating H. cunea lays around 400 eggs on the underside of a leaf.  The eggs are bright green in many pictures but also described as "hair-covered masses of several hundred each" in others.  The hair comes from the female's body.

The female typically clings to the leaf until she dies, in this case covering her last batch of eggs.  I checked the leaf daily and on day 8 a few caterpillars emerged.  these were black-headed, typical of the spring hatch.

Emerging caterpillar
Empty egg cases

After filming them, I took the now dry crisp leaf out to a small elm tree and clipped it onto a fresh leaf.  The next morning they were crawling over a portion of the new leaf, eating the top green surface only.  You can see one emerge in this video.
Leaving the eggs
Skeletonized leaf - University of Florida
The larger next instar will eat both surfaces of the leaf leaving the structure of the leaf with no surface cells.  The final instar completely skeletonizes the leaf, eventually leaving only major veins, a view hidden by the ugly webs we all hate.

Dinner for the first instars

More on the subject is at this University of Florida link.