1036 DISEASES AND INSECTS 



DISEASES AND INSECTS 



sense, a sense of direction, which enables the bee to 

 find its way for a mile or more back to its home. Insects 

 are doubtless able to distinguish the color of objects, 

 and some insects seem to prefer certain colors. Blue 

 is said to be the favorite color of the honey-bee, and 

 violet that of ants; ants are also apparently sensitive 

 to the ultra-violet rays of light, which man cannot per- 

 ceive. It is generally supposed that the shape and high 

 colors of flowers 

 attract insects; 

 but recent ex- 

 periments seem 

 to show that in- 

 sects are guided 

 to flowers by 

 the sense of 

 smell rather 

 than by sight. 

 The hard outer 

 skin of an insect has no nerves distributed in it, 

 hence it is not sensitive; but it is pierced with 

 holes, in which grow hairs that are in connection 

 with nerves at their base. It is by means of these 

 sensory hairs that insects feel, and are sensitive to 

 touch on most parts of the body. Doubtless insects 

 are not deaf, for we know that many of them make 

 sounds, and it must naturally follow that they have 

 ears to hear, for there is every reason to suppose that 

 they make these sounds as love-songs to attract the 



1296. The four stages in an insect's life egg, larva, pupa, imago. The codlin-moth. 

 (Egg much enlarged; others XIJi) 



1297. Nymphs of the four-lined leaf-bug, and adult of the 



tarnished plant-bug. 



The smaller one at the left is the nymph recently hatched. The 

 next is the nymph after the first moult. The imago is shown at 

 the right. Hair lines at the right of nymphs, and small figure near 

 imago indicate the natural size. 



sexes, as a means of communication, or possibly to 

 express their emotions. Some think that bees and 

 ants hear sounds too shrill for our ears. Insects have 

 no true voice, but produce various noises mechanically, 

 either by rapid movements of their wings, which causes 

 the humming of bees and flies, or by friction between 

 roughened surfaces on the body or its appendages, 

 thus producing the rasping sounds or shrill cries or 

 some crickets and grasshoppers. The house-fly hums 

 on F, thus vibrating its wings 335 times in a second, 

 while the wing tone of the honey-bee is A. Usually 

 the males are the musicians of the insect world, but it 

 is the female of the familiar mosquito which does the 

 singing, and the "biting" also. The male mosquito 

 doubtless hears the song of his mate by means of his 

 antenna?, as the song causes the antennal hairs to 

 vibrate rapidly. Organs which are structurally ear- 

 like have been found in "various 

 parts of the body of insects. The 

 common brown grasshoppers of 

 the fields have a large ear on each 

 side of the first segment of the 

 abdomen; one can easily distin- 

 guish with the naked eye the 

 membrane or tympanum stretched 

 over a cavity. Many of 

 the long -horned green 

 grasshoppers, katydids 

 and crickets have two 

 1298. Larva of a sphinx moth. similar ears on the tibia 



of each front leg. Some think that mosquitos have the 

 faculty of the perception of the direction of sound more 

 highly developed than in any other class of animals. 

 Insects undoubtedly possess the sense of taste. When 

 morphine or strychnine was mixed with honey, ants 

 perceived the fraud the moment they began to feed. 

 The substitution of alum for sugar was soon detected 

 by wasps. Bees and wasps seem to have a more deli- 

 cate gustatory 

 sense than flies. 

 Taste organs 

 have been found 

 in many insects, 

 and are usually 

 situated either 

 in the mouth 

 or on the organs 

 immediately 

 surrounding it. 

 Many experiments have shown that the antennae are 

 the principal organs of smell in insects. Blow-flies 

 and cockroaches which have had their antennae removed 

 are not attracted by their favorite food, and male 

 insects find their mates with difficulty when deprived 

 of their antenna?. The familiar world which surrounds 

 us may be a totally different place to insects. To them 

 it may be full of music which we cannot hear, of color 

 which we cannot see, of sensations which we cannot 

 perceive. Do insects think or reason? Why not? 

 Their actions are said to be the result of inherited 

 habit or instinct. But some of them have been seen 

 to do things which require the exercise of instinctive 

 powers so acute and so closely akin to reason that one 

 can hardly escape the conclusion that some insects are 

 endowed with reasoning powers. 



Their number, size and age. Experts guess that 

 there are from 2,000,000 to 10,000,000 different kinds 

 of insects in the world. Only about 400,000 of these 

 have yet been described and named by man. Between 

 30,000 and 40,000 are now known in North America. 

 Four-fifths of all the kinds of animals are insects; some 

 single families of insects are said to contain more 

 species than one can see stars in a clear sky at night; 

 and there are as many butterflies as birds in North 

 America. The larger part of the land animals are 

 insects, and it is asserted that the larger proportion 

 of the animal matter existing 

 on the lands of the globe is 

 probably locked up in the 

 forms of insects. Insects vary 

 in size from little beetles, of 

 which it would take 100, 

 placed end to end, to measure 

 an inch, up to tropical species 

 6 or 8 inches in length, or 

 of equal bulk to a mouse. 

 Insects have a very long, 

 but, as yet, very imperfect- 

 pedigree extending through 

 the geological ages to Silu- 

 rian times. Fossil remains of 

 many different kinds of in- 

 sects have been found in 

 the rocks (Fig. 1295); even 

 such delicate insects as plant- 

 lice left their impress on the 

 rocks ages ago. In the car- 

 boniferous or coal age, the 

 insect world was evidently 

 quite different from that of 

 today, for fossils of veritable 

 insect mammoths have been 

 found; dragon-flies with a 

 wing-expanse of 2 to 3 feet 

 then existed. Insect fossils 

 found in the tertiary rocks 



1299. 

 Tent-caterpillar. 



