The eggs are very small and are usually placed on the lower edge of the leaf. These hatch and the small green worms appear. Throughout the summer there are a number of broods produced and an enormous amount of damage is done. Just before frost the last caterpillars search for protected places where they pass to the pupal or resting stage for the winter. No cocoon is spun by this caterpillar.
Where measures are not taken to control the cabbage worms they destroy much of the cabbage crop each season. The white butterflies can be seen any day during the summer visiting cabbage, mustard, radishes and other similar plants. By destroying all of the worms and millers in the early spring one has less trouble later. This can be done by hand picking, or where the patch is large by spraying with a poison solution to which soap is added to keep the solution from rolling off in large drops. Poison can be used until the heads are well formed, but if the first worms in the spring are destroyed, later spraying is unnecessary though an occasional handpicking will help.
Observations and Study
Cabbage worm feeding, slightly enlarged.
Pupa or chrysalis of cabbage miller.
Go into the garden and examine the cabbage for small green worms which vary from one fourth to a little over an inch in length. What is the nature of their work on the leaf? Where do they feed most, on the outer or inner leaves? Do they eat the entire leaf? How does the work of the young worms differ from that of the larger ones? Do they spin silk? Are they on the top or under side of the leaf? Examine under the dead and dried leaves at the ground and see if you can find small, hard, gray objects which have sharp angles and which are tied to the leaf with a cord of silk. What are these objects? Watch the miller as she visits the cabbage and see if you can find the small eggs which she lays on the under side of the leaves. When she visits a cabbage plant she bends her body up under the outer leaves and stops but a moment, fluttering all the while as she sticks the small egg to the leaf. It is about the size of a small crumb of bread. What does the miller feed on? Does she visit flowers? If so, what flowers?
Breeding Work
Collect a few of the worms and put them in a glass jar with a piece of cabbage leaf. Examine them carefully and watch them crawl. How many legs do they have? Where are they placed on the body? How can they use so many legs while crawling? How many joints are there to the body? Note the short fine hair all over the body which gives it the appearance of green velvet. What color is the head? How does the caterpillar feed? Write a brief description of the worm. Do not mistake it for the cabbage span-worm which is also green, but which walks by humping up its back.