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Malacosoma americanum
I agree with KimSerno. This is an Eastern Tent Caterpillar. They are pretty common around here in the Northeast (I'm in NY).
Gypsy Moth caterpillars look like this:
http://www.projectnoah.org/spottings/107...
Looks like a Tent Caterpillar. Probably the Eastern Tent Caterpillar as you're in NJ. They're in the family Lasiocampidae :)