Millions & Millions of Mice

One morning an Australian rancher swept 28,000 poisoned mice off his veranda. In a neighboring village 544 tons of mice were killed in five months. Hordes of field mice--as many as 80,000 per acre--once appeared in southern California, disappeared after devastating the countryside. In pre-Nazi Norway a steamer ploughed for a quarter of an hour through shoals of mouselike lemmings swimming out to sea via the Trondheim Fjord. In France great plagues of voles (short-tailed field mice) appear approximately every five years, then abruptly disappear. One of Germany's periodic infestations of mice and voles broke out in 1917, ravaged crops so badly that they materially contributed to the nation's final collapse.

Musine Diastole. This roster of rodentry was cited last week by Zoologist Charles Elton of Oxford University. In his 496-page study, Voles, Mice and Lemmings (Oxford; $10), Zoologist Elton investigates one of nature's strangest mysteries--why, all over the planet, hordes of such rodents pop up out of the earth from time to time. Small, silent, fleet, these musine masses scurry tirelessly among the grasses, destroying grain, trees, any other vegetation they can get their teeth into. Then they vanish from the desolated fields as if they had sunk back again into the earth, which remains sieved with their burrows. Fear of their visitations is age-old: Apollo protected the ancients against them. In North Brabant, Holland, St Gertrude is prayed to as a protectress against mice.

But only in the last 20 years have most scientists' eyes opened to the fact that these plagues are periodic, ebbing & flowing almost as regularly as the tides. Says Zoologist Elton: animal populations were formerly thought to be fairly stable, fluctuating only by chance. Now they are known to recur regularly, so that the biomass--"the living fabric of the world" --may be said to pulsate like the diastole and systole of a mighty heart.

Toward Atlantis? The classic example of this pulsation is the periodic appearance of Scandinavian lemmings, which every three to four years rush by thousands to the coasts, then swim far out to sea, where they drown.

The popular belief is that the lemmings' persistent dash to death is an instinctive longing for their former home in the sunken continent of Atlantis. But, notes Elton, the lemmings also surge eastward into the Baltic, northward into the Arctic. Not the whither but the whence, says Elton, explains the lemming migrations. Overcrowding and lack of food in their mountain homes move the lemmings to seek Lebensraum elsewhere. (A few reactionaries stay behind to breed the nucleus of another horde.) The lemmings are great swimmers, and since they have no way of knowing how vast the seas and oceans are, plunge in and perish in their pride.

Interstellar Influence? In other countries the sudden disappearance of rodent swarms is less spectacular. Yet they always disappear. Zoologists still wonder why. In northern Canada "an outburst of mouse-meat" is always accompanied by an increase of foxes, hawks and other mouse-loving predators. But mouse cycles in Britain, where predators have been largely killed off, are as regular and violent as in wilder lands.

As rodents increase, so do rodent epidemics. Nevertheless, epidemics are too erratic to explain the periodic ebb & flow of rodent population. Field mice flourish in dry weather, suffer in wet weather. But mouse cycles recur regardless of weather cycles.

The major mystery is how the animals maintain their fixed cycles in spite of all such interference. Zoologist Elton concludes that the master factor is still unknown. He believes it may prove to be of a hitherto-undetected meteorological nature, hints at possible interstellar influences.

Practical Importance. The discovery that mice erupt in cycles has important practical applications. In 1935 a U.S. zoologist was able to warn orchardists 18 months in advance of the worst mice outbreak New York State ever suffered, helped save thousands of fruit trees.

Awareness of rodent cycles also helps prevent diseases among human beings. In Norway, for example, lemming invasions are accompanied by outbreaks of "lemming fever"--a form of tularemia. Vole outbreaks in India stimulate the dread bubonic plague; in Central Europe, food poisoning ("ptomaine poisoning"); in Africa, a fever of men and sheep.

Mouse Harvests. Sometimes the mice cycles lead to cycles of disaster throughout nature. "Northward, beyond the line where crops will flourish," says Elton, "the mice themselves become a crop, harvested in turn by fox and trapper and trader." From the reports of the Hudson's Bay Company and of Labrador missionaries Elton has found that in the last century fox catches fluctuated in four-year cycles, one year after the cycles of voles in Labrador and lemmings in Ungava (subArctic Quebec).

When the rodents increase, foxes increase. So do hawks, snowy owls, martens and even caribou (because the wolves eat the rodents, which are easier to catch than caribou). When the rodents disappear, the foxes die off, and the snowy owls--"a mass of transfigured lemming" --emigrate to the U.S. Wolves attack the caribou herds again, and survival becomes harder for the caribou-hunting Indians.

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