Within a few years considerable publicity has been given to the supposed possibility of utilizing bats to destroy mosquitoes and thus eliminate malaria from infested areas. One or more bat houses have been built at San Antonio, Texas, for the purpose of assembling bats in large numbers, and many untenable claims have been put forth concerning the benefit to be derived from their services. The Mexican bat is the species which abounds above all others at San Antonio and is the principal species which has occupied the bat houses near town. It is definitely known that bats often fly miles from their roosts when feeding and do not concentrate on any one kind of insect. Examination of the contents of the stomachs of Mexican bats shows that they feed on beetles and numerous other insects, but rarely upon mosquitoes. I have visited many Mexican towns and villages in which every house was haunted by numbers of these bats and where malaria was perennial. The evidence against these animals serving any useful purpose in checking malaria is conclusive.
It may be repeated here, however, that all of our bats are of high utility as insect-destroyers and should be protected. Among the many species of varying habits which exist in the United States, a few make their homes about houses in annoying numbers. In place of killing them to abate the nuisance, it would be better to exclude them from buildings by closing the entrance ways promptly after all have left in the evening, and thus by quiet eviction cause them to find abiding places elsewhere. The destruction of forests, and the consequent absence of the hollow trees where they formerly lived, is mainly responsible for bats and chimney swifts coming to houses for harbor.
THE BIG-EARED DESERT BAT (Antrozous pallidus and its relatives)
(For illustration, [see page 567])
The marvelous variations in structure of the ears and other organs about the heads of insect-eating bats serve probably as microphones by which the flight of their prey may be detected and its direction located with instantaneous certainty. The beautiful accuracy with which this hearing mechanism works must be evident to any one who will take a position where he may have the evening glow of the western sky as a background for flights of bats. It is certain that the small and ineffective eyes these animals possess could never locate their minute flying game and enable them to secure it in the whirling, zigzag courses they pursue, often at a speed and under a control which few, if any, birds could rival.
The great ears of the big-eared desert bats illustrate one form of a highly developed hearing apparatus and give these animals a handsome and strikingly picturesque appearance. This character at once distinguishes them from others of their kind in the United States.
The distribution of this species lies mainly in the arid parts of the Southwestern States and Mexico. It extends from western Texas, southern Colorado, Nevada, and Oregon, south to Queretaro, on the Mexican table-land, and to the southern end of the peninsula of Lower California. The vertical distribution extends from sea-level up to at least 5,000 feet altitude.
By day these desert bats live in crevices and caves in cliffs, in old mining tunnels, hollows in trees, and in sheltered places about the roofs and walls of houses, barns, or other buildings. Their presence in dark hiding places may sometimes be detected by occasional grating squeaks. They appear to lack any musky odor which characterizes so many bats. About the 1st of June each year either one or two young are born, and for a time these cling to the mother’s breast and are carried during her swift flights in pursuit of insect prey.
Often when camping at desert waterholes, I have seen them come in just before dark to drink, scooping up water from the surface while in flight, and then circling back and forth over the damp ground at an elevation of a few yards for the capture of some of the insects common in such places. At such times, with the distant hills mantled with a deepening purple haze and the pulsating heat of the day replaced by the milder temperature of approaching night, these bats could often be seen sharply outlined against the rich orange afterglow of the departed sun. Here and there in the still air flickered and zigzagged multitudes of tiny bats, like black butterflies, and among them the occasional big-eared bats on broad wings appeared huge in contrast. Their wing strokes were slower and shorter than those of the smaller species and impelled them forward in a swift, gliding movement which gave their evolutions a sweeping grace beautiful to see.
In August several years ago, during a visit to the Indian School at Tuba, in the Painted Desert of northern Arizona, I found these bats living in considerable numbers about the buildings. Just before dark they swarmed out and hunted about the surrounding orchards and small fields. One evening my collector shot at one as it circled over a potato field in a small orchard. It continued its flight, circling low among the apple trees as though unhurt, when suddenly it dropped to the ground. Supposing the bat to be wounded, it was cautiously approached and covered with a hat, when, without a struggle, it permitted itself to be picked up by the nape. It then became evident that the bat was unhurt from the shot. The reason for its sudden descent was revealed in the person of a large, fat mole cricket (Stenopalmatus fuscus) which it was holding firmly in its jaws, and so ferociously intent was it in biting and worrying its luscious prey that it paid not the slightest attention to its captor. Finally it was killed by having its chest compressed and died with its bull-dog grip on its prey unbroken.