Monarch - Hodges#4614 (Danaus plexippus) Caterpillar 2nd Instar
Photographed on a common milkweed at Mendon Ponds Park near Rochester, NY on Aug. 10, 2017. Length=8 mm. The year 2017 seemed to be a good one for monarch butterfly breeding in western New York State.
Species page at BugGuide.net