This is a picture of a Gypsy Moth. I'm going to enter it into 
The moths were apparently brought to the United States in the late 1800s as part of an attempt the interbreed them with silkworms. As always seems to happen in these stories they escaped and have slowly been spreading across the United States since then.
I was first made aware of them when they came to my area in the 1990s. In the picture you see a female mouth as she is laying her eggs. That is the egg sack underneath her. When the eggs hatch next spring the caterpillars will float to other trees on a string of silk and eat the leaves, eventually forming a cacoon and becoming moths to start the cycle all over again.
This is really no different than other moths it butterflies but, due to their lack of pickiness of what trees to eat and lack of natural predators, the 500 or so eggs in each egg sack turn into 500 or so moths. You can see how the population can grow quicky.
If the population gets too great trees will die due to lack of foliage. This has left cities and property owners with no choice but to try to combat these pests, with many cities spraying from the air.
Apparently she actually use the hairs on her belly to coat the eggs in a protective fuzz.