Color, protuberances and markings are important features when identifying caterpillars. Four common, and easily identified, caterpillars of note to gardeners are hornworms, cabbage loopers, monarchs and cecropias.
Tomato and tobacco hornworm caterpillars are large, bright green caterpillars approximately the size of a human finger. Both species have a long horn on the posterior end. Tomato hornworms have a black horn while the horn is red in tobacco hornworms. Tobacco hornworms have seven diagonal white streaks along the body and tomato hornworms have eight similar stripes. Both species have small red spots running the length of the body. These caterpillars are common garden pests capable of defoliating vegetable crops.
Cabbage looper caterpillars are bright green, inchworm-sized caterpillars with a thin white stripe running the length of the body. Their looping motion is the result of the presence of both fore and hind legs but no middle appendages. Despite their name, cabbage loopers feed on nearly any green garden plant.
Monarch butterfly caterpillars reach 2 inches in length and possess distinct black, yellow and white stripes. They have a pair of black antennae at the head and a similar pair of black horns in the rear. Due to their milkweed diet, the caterpillars are unpalatable to predators. Many people wish to attract the caterpillars because of a fondness for the show orange butterflies they become.
The caterpillar of the cecropia moth is roughly the size and color of a hornworm, but these caterpillars possess many spiked protuberances in blue, yellow and red instead of horns. These caterpillars feed on fruit tree leaves but pose little threat to trees or orchards. With wingspans of 6 inches, cecropia moths are the largest moths in North America.