How to Identify Large Green Caterpillars

Any child who remembers Alice's chat with the hookah-smoking caterpillar in Wonderland will delight at the squiggly green insects in a yard. The gardener of the family may, however, feel differently. Huge caterpillars of any color have huge appetites and may work through tender new foliage at an alarming rate. If the child within you wants to know the names of these beasties before deciding whether or not to evict them from paradise, then know how to identify them.

Naming Names

When you have guests in the garden, it's always polite to learn their names. A garden's big green caterpillars -- those over 2 inches long -- are likely to be one of the following specimens:

  • The larvae of a member of the Saturniidae family of moths, also called royal moths and silkworm moths.
  • The larvae -- known as hornworms -- of a member of the Sphingidae family of moths, also called sphinx moths.

Moth Magic

Butterflies and moths go through a multistage metamorphosis in their lifetimes, changing from egg to larva to pupa to adult. In the larval stage, they are , with long, cylindrical bodies and defined heads. Once hatched, caterpillars grow from small to big, shedding their exoskeletons up to nine times before pupating. They require food to fuel this growth, often looking to tender greens in the garden, chowing down an impressive amount of foliage during this "eating" stage of the metamorphosis. Hornworms are considered garden pests, but royal moth larvae are not because only a few appear in a garden at one time.

Who's Who

Caterpillars don't get to eat a bit of mushroom and decide how big to grow. Because of that, size is a good way to identify them. "Big" caterpillars, those 3 inches or longer, are in the minority, and they stand out because of their size. Generally, the larvae of royal moths are largest, and any caterpillar over 3 inches is likely one of their number. Hornworms -- both tobacco and tomato varieties -- are roughly 3 inches long when mature.

Caterpillars' markings are particular enough that you can identify most species quite easily if you get close enough. Caterpillars' period of activity is another clue to their identification.

Royal and Silkworm Moths

  • Polyphemus moth larvae
    Almost 3 inches, bright green with brown head, thin yellow line on abdominal segments, present May through October
  • Actias Luna moth larvae over 3 inches, lime-green body with three pair of true legs toward the front and five pair of false legs toward the back of the body, present spring through fall
  • Hickory horned devil 4 to 5 inches, dull green with darker spines, present July through October
  • Imperial moth larvae 4 inches, light to dark green with orange head, white hair on body, present June through August
  • Io moth larvae 2 to 3 inches long, pale lime green with red-brown and white stripes along its length, covered with spines that have black ends, present July through October
  • Cecropia moth larvae
    3 to 4 inches, pea green with orange and pale-blue knobs, May through August

Hornworms/Sphinx

  • Tobacco hornworm
    3 inches long, light green with angled white lines on sides and red horn at end of back, present June through September
  • Tomato hornworm
    3 inches long, light green with angled white lines on sides pointing toward head or in V shape and black horn at end of back, present June through September
  • Whitelined sphinx
    3 inches long, dull-green body with two yellow and black lines running parallel down back, present spring to early fall