During the summer months the worms are common, being most abundant in August. In the fall the mature worms go into the ground and change from the worm to a large, oval, brown pupa with a jug-handle-like appendage on the under side. These are often turned up when the garden is plowed in the spring. After tomato plants are well started the large greyish humming-bird-like moths comes from the ground and begin laying eggs. The moth expands from four to six inches and is often seen at dusk visiting the blossoms of "jimson weed" and other large tube flowers. They are also found around lights at night.
Young tomato worm.
Where they are troublesome the plants should either be sprayed with a poison when the injury is first noticed or else the worms should be picked off and destroyed. There is a small parasitic wasp which is very helpful in destroying this caterpillar. They live inside the worm and when mature bore out through the skin on the sides and back where they spin small white egg-like cocoons from which later the small wasps emerge. Often a hundred or more may come out of one worm.
Study and Observation
Observe the worms where they are at work on tomatoes. Disturb them and hear them grind their jaws together. Do they eat the foliage rapidly? Dust a little Paris green on the foliage where a worm is eating and see what happens in half an hour. Collect a number of the worms in a glass fruit can and give them tomato leaves to eat and watch them grow. How many segments are there to the body? How many of the segments have small black spots on either side? These are holes through which the worm breathes. Is the horn at the end of the body stiff enough to stick into your hand? This is thought to be a sting but it is only an ornament and is entirely harmless. When full grown they will burrow into the sand in the jar and change to the pupa.
Full-fed tomato worm slightly reduced.
Chrysalis or pupa of tomato worm. Note the jug-handle-like sheaths enclosing the proboscis.