The cabbage looper, Trichoplusia ni, is one to the most destructive insect pests of lettuce and cole crops; broccoli, cabbage and cauliflower. The looper larvae also feed on tomatoes, cotton, and celery as well as several species of weeds. Alfalfa looper, Autographa californica, is similar in appearance to cabbage looper and also feeds on lettuce, but cabbage looper is the predominate species. The two species need not be distinguished when monitoring vegetable fields as the damage, action thresholds and controls are the same for both species.
Cabbage looper gets its name from the crop that is its primary host, cabbage, and from its looping appearance when walking. A looper larva has three pairs of true legs in the front of its snake-like body and three pairs of fatter unjointed prolegs near the rear of its body. When the larva moves it forms a "loop" by holding on with the front legs, arching the middle section of its body bringing the prolegs in the rear forward, and then extends the front of the body forward by releasing the front legs. This looping motion is repeated over again and again to propel the insect forward; therefore, entomologists and lay people alike call these larvae loopers.