Answer: Caterpillars are larvae (the "worm" forms) of insects in the order Lepidoptera??the butterflies, skippers, and moths. In number of species known, Lepidoptera is the second largest of all insect orders. Consequently, caterpillars are numerous; more than 11,000 species occur in North America, with over 5,000 species in the eastern United States alone. Most caterpillars are plant feeders. They occur on a wide variety of plants, and many are serious pests. Caterpillars are among the most common of all insect forms found on foliage of forest, shade, and ornamental trees. Most are host specific - tomato hornworms feed exclusively on foliage of plants in the Solanaceae family, but lookalike hornworms can be found on ash trees.
Hornworms are larvae of sphinx moths, sometimes called hawk moths or hummingbird moths (Family Sphingidae). These are rather large caterpillars, 2 to 4 inches long. Bodies are generally smooth, except for the characteristic sharp, but harmless, spine or "horn" arising from the top of the eighth abdominal segment. Several species of hornworms feed on foliage of trees. In addition to tomatoes, tomato hornworms (Manduca quinquemaculata) feed on tobacco, eggplant, potato, and pepper, as well as related weeds of the plant family Solanaceae. Two examples of related hornworms are catalpa sphinx (Ceratomia catalpae), which feed on catalpa, and waved sphinx (Ceratomia undulosa), which feed on ash tree leaves. What you found in your ash tree looked very much like a tomato hornworm, but it was a different species.
Hope this clarifies things for you.
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