the hay crop on 30,000 acres. 18 In an Iowa nursery over 3,000 trees were girdled in one season by rabbits; and in a Maryland nursery 2,000 out of 4,000 trees were ruined.

Mice

Mice are responsible for a loss of $3,000,000 yearly in the United States. Short-tailed field mice appeared on the Humboldt River in Nevada in 1907 and by November there were from 8,000 to 12,000 per acre. During the summer they ruined one-third of the alfalfa, totally destroying many fields, 15,000 out of 20,000 acres having to be replanted. They destroyed three-fourths of the potatoes, badly damaged the remainder and severely injured the beets and carrots. They girdled and killed most of the young shade trees planted along the irrigation ditches and about the fields. A conservative estimate of the losses in this district was $250,000. Nature started to even the account by collecting some 2,000 predacious birds (hawks, owls, gulls, crows, ravens and herons) and 1,000 carnivorous mammals (skunks, weasels and badgers) which ate some 45,000 mice a day or 1,350,000 a month. The mice had increased rapidly for a couple of years. Then came the plague and then a sudden decrease for which the animals mentioned and some disease probably were the chief factors.14

Rats

The rats, of which the common brown rat is the most important, cause a loss of not less than $200,000,000 yearly, it being estimated that there are as many rats as men in the United States and that each rat causes a loss of some $2.00 yearly.

The constant labor of an army of more than 200,000 men is required to produce the materials eaten and destroyed by rats. If half this loss were represented by grain destroyed, it would take about 5,000,000 acres to produce it. In 1908 the Biological Survey made a careful study of rat infestations in two cities, Washington and Baltimore, with the result that the actual losses of produce and other property amounting annually to $400,000 and $700,000, respectively, were revealed. These sums are nearly in ratio to the populations. The Women's Municipal League of Boston recently announced that losses from rats in that city amounted to $1,350,000 each year. Losses in Pittsburgh, Pa., have been estimated at over $1,000,000 a year. 15

Furthermore, rats are one of the most important agencies in the distribution of such diseases as the bubonic plague. Quite in contrast to the above stands the record of the bats which are insectivorous and of great value to man in his fight against his enemies.

Certain of our hawks and owls feed on rodents. In late fall and winter the sparrow hawk feeds largely on meadow and house mice. The staple food of the long-eared owl is meadow mice. Three-fourths of the diet of the screech owl is mice. Nearly 9 per cent of the food of nestling crows is of rodents, rabbits being preferred, and the adult crow eats them as well. Most of these birds deserve to be protected rather than destroyed by man simply because they do some damage.

DIFFICULTIES OF PEST CONTROL

Effects of Bird Destruction

Enough evidence has been offered to demonstrate that the wholesale killing of birds is likely to have very disastrous consequences for man himself. It is doubtful if man can carry on agriculture profitably without the assistance of birds in the face of insect competition. Years ago Forbush estimated that the destruction of bird life in this country had already imposed a burden equal to $1.67 a year per acre of cultivated ground. How serious this is may be seen when we recall that the total tax collected on typical Illinois farm lands for the year 1926 was only $1.50 per acre, yet the farmer was complaining. It is admitted that some birds have probably increased in numbers. This is obviously true of the English sparrow. It appears to be true of the robin in many places. As the Middle West was settled and trees were planted in the towns, an increase of bird life was noted. Some species have enjoyed the protection offered by man and some have profited by the killing off of their own enemies by man. The point is that man must count the cost and not kill indiscriminately lest he injure himself.

The same argument holds as to his attitude towards many of the smaller mammals. The opossum seems to have extended its range since the white man came, but there is evidence that its numbers are declining. This is true of the coon and the skunk. While these all feed to some extent on man's crops they also destroy vast numbers of insects and mice. Thus they more than repay man for the amount they eat.

The suggestion has been made already that man may try in the future to utilize helpful forms of life in his contest with his enemies. In some instances this has been tried and the results have not been too satisfactory.

Unsatisfactory Remedies

Troubled by the ravages of the spring canker worm on the shade trees, the directors of the Brooklyn Institute introduced a few pairs of English sparrows in 1850. These did not thrive and later others were introduced. These throve as did others brought to other places. They saved the shade trees but then forgot to commit suicide and began to increase until as Hornaday says: "It is a national sorrow almost too great to be endured." The bird has spread into almost every corner of our country, often driving the native birds out of the towns. As noted, it is now the second most common bird in the northeastern states. It is noisy, quarrelsome and dirty, preferring grain to weeds and in towns has fed largely on refuse grain. It will eat some insects and may prove to be valuable later on. There seems to have been a stopping of the increase about 1912. Another bird of somewhat doubtful value is the European starling, first liberated in New York City in 1890. It is spreading rapidly over the East and winters in great flocks in Pennsylvania and Delaware. It has proven a menace to the fruit crop in Australia. Much to their credit both the sparrow and the starling eat the Japanese beetle.

In 1872 the mongoose, which in its East Indian home feeds on rats and snakes and is often kept as a pet, was introduced into Barbados and Jamaica to get rid of the rats which were injuring the sugar cane. The attempt was only too successful. The mongoose began to attack all forms of ground life and everywhere became a scourge.

The most noticeable result

was not a diminution in the numbers of the rats, but a marked decrease in the numbers of the small doves and other ground nesting birds and of the lizards, coupled with a great increase in the numbers of obnoxious insects. For instance on St. Lucia the screw-worm flies soon became abundant and a terrible pest to live stock. Why? Because these flies, which like to sun themselves on rocks and fence rails, fall an easy prey to the numerous small lizards which frequent just such situations, and the mongoose feeds largely upon these little lizards.16

Owing to the reduction of the birds Jamaica is having trouble with ticks introduced from Mexico. Meantime the mongoose has reached other Caribbean Islands, including Porto Rico and Santo Domingo. Our government is greatly worried lest it find its way here and the importation is carefully regulated. Yet one was found in the Middle West a couple of years ago.

Rabbits

The English introduced the rabbit into Australia about 1860. Lacking local enemies, it increased so rapidly that, as in New Zealand, it became a question whether the colonists should not move out rather than try to fight it. It became necessary to build rabbit-proof fences and a few years ago over 100,000 miles of such fence was in use, observers stating that the grass often grew tall on one side of the fence whereas the other was almost barren. Partial compensation has been found in the shipment of rabbit skins to Europe, the number from New Zealand even before the war had reached a total of 12,000,000. During the war, rabbits were exported as food, owing to the meat shortage in England. The frozen, dressed rabbits exported in 1919 totaled 1,372,869.

Cats

In eastern America the domestic cat dumped by the wayside by some "kind-hearted" person or deserted by its owners has often gone wild and has become one of the serious enemies of native birds.

Disease

The story of man's warfare against disease is reserved for a later chapter. Here we must note, however, the fact that insects are of importance to man as hosts or carriers of some of the worst diseases of man and his domestic plants and animals. The mosquito is the carrier of malaria and yellow fever. The flea transmits the bubonic plague. The house fly helps to spread typhoid. Man helps to spread these dread enemies by the development of his commerce. He carried the mosquito infected with yellow fever in his ships just as he carried the rats infected with bubonic plague. Mosquitoes travel on his trains. Various insects ride in his automobiles to fall off and start centers of infestation. Likewise man carries plant diseases such as the fungus, which has destroyed practically all the "spreading chestnut" trees of the East, which seems to have come in some unknown way from Asia.