The Great Lakes fisheries in Illinois waters are of insignificant propor tions. The total longshore product for Conk and Lake counties during the last census year was 812.500—about 82,000 less than the sum derived from our river turtles alone.
The fisheries of the state are of sufficient economic interest to make it the duty of all concerned to preserve them carefully and to take all prac ticable measures for their improvement and development.' The accompanying table shows in detail the fish catch in pounds for a single year. The stations are arranged in order from Henry, Marshall County, downstream to Meppen, Calhoun County, a distance of about 200 miles.
Insects.—In addition to the vertebrate animals already mentioned, Illinois is the home of myriads of invertebrates, the most important groups of which are the insects and mollusks.
The insects of the state are of great economic importance because of their relation to field crops, vegetable gardens, flowers, shrubs, and trees. Injurious insects are reduced in number and their ravages greatly lessened by the work of insec tivorous birds, predaceous and parasitic insects, and by man. The study of the life-histories of injurious insects and the best methods of combating them is carried on by state and national governments, and the results are widely published.
Among the more injurious insects to Illinois field crops are the chinch bug, Hessian fly, army worm, cut worm, corn-root aphis, corn-root worm, and green-oat aphis. Among the
garden pests are found the potato beetle, cabbage worm, striped cucumber beetle, squash bug, and aphids. Some of the insects which infest trees are the codling moth, San Jose scale, tent caterpillar, peach-tree borer, wooly apple aphis, and the tussock moth.
Many insects arc of value to man because they destroy injurious insects. These helpful insects are predaceous if they eat their prey; parasitic, if they live upon the bodies of other insects. Among the predaceous insects are the lady-bird beetles, lace-winged flies, and ground beetles. Some of the important parasitic insects are the braconoid flies, ichneumon flies, and chalcis flies.
Mollusks.—Snails and fresh-water mussels, or "clams," are the chief representatives of the mollusks in Illinois. Mussels are abundant in the principal streams of the state, and "mussel ing" has been carried on extensively on the Illinois, Mississippi, Ohio, and Wabash rivers. The shells are sold by the ton to button factories; the "meats" make good fertilizers. Pearls are sometimes found in the mussels. When "musseling" was at its height on the Illinois River, large jewelry establishments sent their representatives up and down the river in motor boats to purchase pearls of the fishermen. Prices varied from $3 for the smaller specimens to more than $2,500 for the largest and most perfect pearls.