Cotton Worm, the caterpillar of an owlet moth, of the tribe of noctuae (N. xylina, Say). The perfect insect is of a triangular shape, about an inch in length; the upper wings reddish gray, a dark spot with a whitish centre in the middle; the under wings are darker. The caterpillars have 16 legs, but the foremost prop legs are so short that in creeping they arch up the back like the geometers or span worms; the color is green, with light yellow stripes and black dots along the back; the second and third generations are darker than the first; they grow to the length of an inch and a half. The eggs, from 10 to 15, are deposited on the under surface of the tender leaves, to which they are firmly attached, and of a color resembling the leaf; the period of incubation is variously stated from 6 to 15 days, depending probably on the heat of the season; the time of hatching is at night, and the young begin to eat very soon, growing very rapidly; the skin is changed several times before they attain their full growth.
In 15 to 20 days after attaining the full size they cease to feed, and form an imperfect cocoon of a leaf and silk; in this the chrysalis state is passed, from 10 to 12 days; after this the moths lay their eggs, and die after a period of about a week, or, according to some observers, survive mild winters. This insect is in some years exceedingly destructive to the cotton, sometimes cutting off the entire crop of certain districts; it appears often in a sudden and unaccountable manner, as if it must migrate from the south. They were first noticed as destroyers of cotton about the year 1800, since which their ravages have been more or less serious almost every year; it is believed by some that they appear at intervals of three years in the same districts, and that their greatest ravages occur after intervals of 21 years; the years 1804, 1825, and 1846 were remarkable in this respect; the time of year varies from June to October. A moderate degree of cold is sufficient to kill them, though moisture and strong winds do not appear to disturb them. They devour both the short-staple and the long-staple cotton, and rarely, if ever, touch any other plant. When they appear early in the season, there are usually three broods.
Dr. Burnett is of opinion that this insect comes from South America, and that the last brood perish entirely, either from cold or starvation, leaving no progeny behind them. Fires in the fields have been recommended as attracting and destroying this moth; white cotton flags, about a yard square, are said to attract it, and to be used as deposits for the eggs; great numbers may be caught by molasses and vinegar spread on plates. But these and similar contrivances will be of little avail until the exact appearance of the first moths is ascertained; then their speedy destruction would prevent the production of the second and third broods, and thus limit, if it did not arrest, their ravages. - Another insect destroying great numbers of cotton buds is the boll-worm moth, belonging to the same tribe of noctuae, and probably to the genus heliothes. This is a tawny, yellowish moth, which may be seen toward evening, in summer and autumn, hovering over the cotton blooms, and depositing a single egg in each flower; the egg is hatched in three or four days, and the worm eats its way into the centre of the boll, causing its premature fall; the insect instinctively leaves the boll when it is about to fall, and enters another, and finally attacks the nearly matured bolls, rendering the cotton rotten and useless.
The caterpillars have 16 feet, creeping with a gradual motion, unlike the true cotton worm; they vary much in color, some being green, others brown, but all more or less spotted with black, and having a few short hairs. A single moth will lay 500 eggs, and, as three broods are produced in a year, a whole field will be very soon infested with them. - These are the two greatest enemies on the cotton plantations, and the same remedies are effectual against both. In the "Agricultural Report of the Commissioner of Patents" for 1855 is an excellent article by Townend Glover on the insects found on the cotton plant, on the stalk, on the leaf, on the terminal shoots, on the flower, and on the boll, whether injurious, beneficial, or indifferent. Many cotton worms are destroyed by spiders, beetles, and ichneumon flies.
Cotton Worm. - 1, 2. Noctua xylina and larva. 3, 4. Heli-othes and larva.