Nothing has done me more good than to hear that the cicadas have all got a plague. The newspapers are carrying stories about it. A blue-green mold which is always more or less present on the summer cicada has attacked the seventeen-year variety with terrific vehemence, and mycologists and entomologists alike are excited about it. Apparently the fungus does not kill more than a fraction of the dog-day cicadas, who have probably built up a certain resistance to it. The periodical cicadas, emerging in tremendous numbers, comparable to overcrowding in our city slums, are seized upon by the disease and their vitals swiftly eaten out. Spores for spreading the malady push out from the corpses and sow the air with death to others.
So, though the cicadas emerge by the billions of billions in fourteen different states, a check upon them is always waiting. I have found several cicadas being carried off by predatory wasps, and the woods about the house are suddenly alive with woodpeckers, chewinks, orioles, flickers, sparrows, grackles and robins, fattening on the winged harvest.
There is no diminution yet in the uproar, but my lightened heart gives me grace to take some interest in the biology of the creatures. The period of seventeen years is varied, in the southern states, to thirteen years, and the recurrence of the adults is further made irregular by the fact that there are more than a score of broods in different parts of the country, each having its own years for the rhythmic emergence, or, as we might say, starting off on a different beat, though all keeping the same rhythm. In some areas several broods overlap, so that the cicada years occur oftener than every seventeen years. Some of the broods occupy immense areas, but others are more restricted and feeble.
No other insect in the world has such a long life as this, nor a life history so disproportionate. To be sure, the summer cicada spends a year underground and another of life above it, but as there are two broods, we always have the common cicada with us. But the periodical cicada spends seventeen years as grub, and sometimes no better than seventeen days as a free creature of the sunlight and air.
The fate of the insect seems miserable enough to us, but in fact the strange life history is distinctly advantageous to the creature itself. Its seventeen years underground do not represent prison to the cicada, but comfort and safety, such as a mole or an earthworm knows. It is only when this animal, which we must regard as a naturally subterranean species, takes the dangerous step of emerging into the air that it has any reason to sorrow. For, as so often happens, the moment of sexual maturity is also the moment of predestined death. Nature flings the sexes at each other and then, having no more use of them, she draws her sword and slays them.
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