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caterpillar, and the tent caterpillar; the last spins a tent which serves as a shelter in wet weather.

The larvæ of some moths damage the trees by boring into the wood of the tree on which they live.

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Such are the peach, apple, and other fruit-tree borers common in our orchards. Some species of beetles produce boring larvæ which eat their way into trees and then feed upon the sap of the tree. Many trees in our Adirondack Forest Reserve annually succumb to these pests. Many trees are killed because the beetle girdles the tree, cutting through the tubes in the cambium region. Most fallen logs will repay

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a search for the larvæ which bore between the bark and wood.

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Among the bugs most destructive to trees are the scale insect and the plant lice, or aphids. The San José scale, a native of China, was introduced into the fruit groves of California about 1870 and has spread all over the country. It lives upon numerous plants, and is one of the worst pests this country has seen. It is interesting to know that a ladybird beetle, which has also been imported, is the most effective agent in keeping this pest in check. Insects of the House or Storehouse. The weevils are the greatest pests, frequently ruining tons of stored corn, wheat, and other cereals. Roaches feed on almost any kind of breadstuffs as well as on clothing. The carpet beetle is a recognized foe of the housekeeper, the larvæ feeding upon all sorts of woolen material. The larvæ of the clothes moth do an immense amount of damage to stored clothing especially. Fleas, lice, and especially bedbugs are among man's personal foes.1

Beneficial Insects. Fortunately for mankind, many insects. are found which are of use because they either prey upon injurious

1 Directions for the treatment of these pests may be found in pamphlets issued by the U.S. Department of Agriculture.

insects or become parasites upon them, eventually destroying them. The ichneumon flies are examples already mentioned. They undoubtedly do much in keeping down the number of destructive caterpillars.

Several beetles are of value to man. Most important of these is the natural enemy of the orange-tree scale, the ladybug, or ladybird beetle. In New York state it may often be found feeding upon the plant lice, or aphids, which live on rosebushes. The carrion beetles and many water beetles act as scavengers. sexton beetles bury dead carcasses of animals. countries are particularly useful as scavengers.

The

Ants in tropical

Insects, besides pollinating flowers, often do a service by eating harmful weeds. Thus many harmful plants are kept in check. We have noted that they spin silk, thus forming clothing, that in some cases they are preyed upon, and support an enormous multitude of birds, fishes, and other animals with food. Make a balance sheet showing the benefits and harm done man by insects.

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How the Damage done by Insects is Controlled. bating of insects by the farmer is controlled and directed by two bodies of men, both of which have the same end in view. These are the Bureau of Entomology of the United States Department of Agriculture and the various state experiment stations.

The Bureau of Entomology works in harmony with the other divisions of the Department of Agriculture, giving the time of its experts to the problems of controlling insects which, for good or ill, influence man's welfare in this country. Such problems as the destruction of the malarial mosquito and control of the typhoid fly; the destruction of harmful insects by the introduction of their natural enemies, plant or animal; the perfecting of the honeybee (see Hodge, Nature Study and Life, page 240), and the introduction of new species of insects to pollinate flowers not native to this country (see Blastophaga, page 45), are some to which these men are now devoting their time.

All the states and territories (except Indian Territory) have, since 1888, established state experiment stations, which work in coöperation with the government in the war upon injurious insects. These stations are often connected with colleges, so that young

men who are interested in this kind of natural science may have opportunity to learn and to help.

The good done by these means directly and indirectly is very great. Bulletins are published by the various state stations and by the Department of Agriculture, most of which may be obtained free. The most interesting of these from the high school standpoint are the Farmers' Bulletins, issued by the Department of Agriculture, and the Nature Study pamphlets issued by the Cornell University in New York state.

REFERENCE BOOKS

ELEMENTARY

Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American Book Company.

Craigin, Our Insect Friends and Foes. G. P. Putnam's Sons.

Crary, Insects and their Near Relatives and Birds. J. Blakiston's Son and Company.

Dahlgren, The Malarial Mosquito. Guide Leaflet 27, American Museum of Natural History.

Davison, Practical Zoology. American Book Company.

Dickinson, Moths and Butterflies. Henry Holt and Company.

Doane, Insects and Disease. Henry Holt and Company.

Farmers' Bulletins, 45, 59, 70, 78, 99, 155.

Howard, L. O., Insects as Carriers of Disease. Year Book, U.S. Department of Agriculture, 1902.

Howard, L. O., Mosquitoes. McClure, Phillips, and Company.

Lubbock, Bees, Ants, and Wasps. D. Appleton and Company.

ADVANCED

Bulletins of Division of Entomology, 1, 4, 5, 12, 16, 19, 23, 33, 34, 35, 36, 47, 48, 51. Folsom, Entomology with Reference to its Biological and Economic Aspects. P. Blakiston's Son and Company.

Sanderson, E. D., Insects injurious to Staple Crops. John Wiley and Sons.
Wheeler, Ants. The Macmillan Company.

XXI. THE MOLLUSKS

Problem XXXIII (Optional). A study of mollusks and their enemies with reference to their economic importance. (Laboratory Manual, Prob. XXXIII.)

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To the average high school pupil a clam or oyster on the half shell" is a familiar object. The soft body" of the animal lying between the two protecting" valves" of the shell gives the name to this group (Latin mollis-soft). Most mollusks have a limy shell, either bivalve (two-valved), as the oyster, clam, mussel, and scallop, or univalve, as in the snail. Usually the univalve shell is spiral in form, some of nature's most beautiful objects being the spiral shells of some marine forms. Still other mollusks, for example, the garden slug, have no external shell whatever.

This limy shell envelope when present, is formed from the outer edge and surface of a delicate body covering called the mantle. The mantle may be found in the opened oyster or clam

sticking close to the inside of the valve of the shell in which the body rests. Between the mantle and the body of the clam or oyster is a space, the mantle cavity. In the space hang the gills, platelike striated structures. By means of cilia on the inner surface of the mantle and on the gills a constant current of water is maintained through the mantle cavity bearing oxygen to the gills and carbon dioxide away. This current of water passes, in most mollusks, into and out from the mantle cavity through the siphons, the muscular tubes forming the "neck" of the "soft clam" being an example of such an organ.

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Fulgar, a univalve mollusk common in Long Island Sound, which does much harm by boring into the shells of edible mollusks.

The food of clams or oysters consists of tiny organisms, plant and animal, which are carried in the current of water to the mouth of the animal, this water current being maintained in part by the action of cilia on the palps or liplike flaps (p. 269) surrounding the mouth. A single muscular foot aids in locomotion when the animal moves about. Many mollusks, as the oyster, are fixed when adult.

The shallow water of bays and other quiet bodies of salt water where clams and oysters live, literally swarm with tiny plants. The conditions for the growth of such plants is ideal. Water from the rivers containing organic waste and depositing daily its load of mud on the bottom

gives one basis for the support of these plants. The carbon dioxide from the thousands of species of fish, mollusks, crustaceans, worms, and other forms of animal life gives another source of raw food material for the plant. The sunlight penetrating through the shallow waters supplies the energy for making the food. Thus conditions are ideal for rapid multiplication; hence the water becomes alive with all kinds of plant life, especially the lower forms. Among these plants are always found bacteria, both harmless and harmful. Mollusks feed upon these plants, including the bacteria; man feeds on the mollusks, and, if he eats them raw, may eat living bacteria as well. Thus disease might result, and, as a matter of fact, epidemics of typhoid fever have been traced to such a source. Some Common Mollusks. The fresh-water clam, a common resident in shallow water in inland ponds and rivers, although not useful

for food to man, has become the source of a very important industry. The making of pearl buttons has so depleted the number of adult clams in our Middle West that the state and United States governments have undertaken the study of the life habits of these animals with a view to restocking the rivers. The development of the fresh-water clam or The egg develops into a free-swimming larval form which fastens to the gills of a fish and there lives as a parasite until almost mature. Then it drops off and begins life in the sand of the river or lake where it lives.

Shell of fresh-water clam, the left half polished to show the prismatic layer from which buttons are made.

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mussel is complicated.

The Oyster. The chief difference between the oyster and the clam lies in the fact that the oyster is fastened by one valve to some solid object, while the clam or fresh-water mussel

moves about. This results in an asymmetry in the shell of the oyster.

Oysters are never found in muddy localities, for in such places they would be quickly smothered by the sediment in the

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metry.

water. They are found in nature clinging Shell of oyster, showing asymto stones or on shells or other objects which project a little above the bottom. food is abundant and oxygen is obtained from the water surrounding them. Hence oyster raisers throw oyster shells into the water and the young oysters attach themselves.

In some parts of Europe and this country where oysters are raised ar

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