Stephen St,. Jean, age 13, of Coventry, Rhode Island, for his question:
Why are there so many locust plagues?
In 1953, swarms of noisy locusts appeared in Indiana. Entymologists predicted that they would return again in the summer of 1970 17 years later. However, among themselves, these scientists did not refer to these insects as locusts. Actually, they are cicadas and not related to the true locusts that so often erupt in plagues, stripping the countryside of all its greenery.
Sudden population explosions often occur in the insect world, or so it seems. Actually, the multitudes were always with us as eggs or nymphs or in other unrecognized forms. We notice the teeming hordes only when they suddenly emerge as winged adults and take to the air. The locusts are world famous, and dreaded, for these teeming explosions. Suddenly they emerge in zillions and the hungry horde swarms off, devouring every leaf, every blade of grass in its path. Some species swarm and migrate every few years, others seem to erupt at unpredictable intervals.
These true locusts are grasshopper relatives and much research on them has been done in recent years. Their life cycle is an incomplete metamorphosis. The eggs become nymphs, small wingless copies of the adults. The nymphs grow bigger by molting their skins and emerge, complete with wings, after their final molt. As adults, they live through several hungry months, devouring the greenery.
Entymologists now suspect that their sudden population explosions may be related to climate. Their numbers remain normal during several normal seasons. But during an extra good summer, when food is abundant, the females lay more, many more, eggs. If the next season happens to be poor, the teeming nymphs crowd around the scanty food supplies. It is thought that this crowding of young males and females causes the females to mature earlier. They produce more broods and soon this super crop of nymphs emerges from the final molt. Famished for food, it takes to the air and migrates and a hungry horde of locusts.
These true locust plagues can strip miles of greenery but the so called 17 year locusts do not. They are cicadas, very different insects who eat nothing during their adult lives. They are about the same size as locusts and even noisier. They too have incomplete metamorphosis. But their nymphs live~underground for 17 years, sipping sap from tree roots. Finally, as if at some mysterious signal, the nymphs go upstairs. They climb up tree trunks and shed their skins for the last time. Suddenly the air is filled with their gauzy wings and their raucus voices. In one hectic week, the cicadas mate, lay their eggs and die. The eggs are placed in twigs. In six weeks the nymphs hatch and fall to the ground. This brood will not emerge for 17 years. But other, perhaps smaller, cicada broods may be timed to emerge during the intervening years.
The true locusts have a pair of leathery forewings and a pair of papery hind wings, unfolded only for flying. They produce several broods of eggs during the summer season. The handsome cicadas have two pairs of long, gauzy wings and usually bright red eyes. Some species mature in a year or so, others take 17 years. But the females lay only one brood of eggs in a lifetime.