Page:Insects - Their Ways and Means of Living.djvu/51
bodies to the object of contact. The young parasites thus palmed off by their mother on the grasshopper, who has no idea what has happened to him, make their way to the base of the wing of their unwitting host, where they find a tender membranous area which they penetrate and thereby enter the body of the victim. Here they feed upon the liquids or tissues of the now helpless insect and grow to maturity in from ten to thirty days. Meanwhile, however, the grasshopper bas died; and when the parasites are full grown, they leave the dead body and bury themselves in the earth to a depth of from two to six inches. Here they undergo the transformation that will give them the form of their parents, and when they attain this stage they issue from the earth as adult winged flies. Thus, one insect is destroyed that another may live.
ls the Sarcophaga kellyi a creature of uncanny shrewdness, an ingenious inventor of a novel way for avoiding the work of caring for her offspring? Certainly her method is an improvement on that of leaving one's newborn progeny on a stranger's doorstep, for the victim of the fly must accept the responsibility thrust upon him whether he will or not. But Doctor Kelly tells us that the flies do not know grasshoppers from other flying insects, such as moths and butterflies, in which their maggots do not find congenial hosts and never reach maturity. Furthermore, he says, the ardent fly mothers will go after pieces of crumpled paper thrown into the wind and will discharge their maggots upon them, to which the helpless infants cling without hope of survival. Such performances, and many similar ones that could be recounted of other insects, show that instinct is indeed blind and depends, not upon foresight, but on some mechanical action of the nervous system, which gives the desired result in the majority of cases but which is not guarded against unusual conditions or emergencies.
When we consider the many perfected instincts among insects, we are often shocked to find apparent cases of