The Strength of the Frail

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Nature Magazine, October 1948

Under an old apple tree in my Insect Garden, a curious thing has happened. A tiny red mite, dropping through the air from the leaves above, has landed on the open page of a notebook. It runs over the paper in curves and curlicues. Each time it comes to the wet ink of a freshly written line, it pauses for a long time as though on the bank of an impassable river. Then I notice its body is turning darker-is losing its brilliant red. The mite is drinking the carbon ink.

Eight times it stops, and eight times it drinks from the black stream of the ink-trail. Only its legs retain their original color. Its round body, swollen with carbon ink, looks like a period mark that has sprouted legs and is running about over the page. Yet, this perambulating period mark shows no ill effects from its intemperance. The black mite is as lively as the red mite had been. The ink in its system has neither slowed it down nor upset its digestion. When last I saw it, it was following the curlicues of its hurried trail along the edge and over the edge of the notebook with as much energy and speed as before.


Mites imbibing ink, cockroaches consuming glue, termites eating wood, beetles stowing away mustard plasters-these are only a few of many instances of small creatures that thrive on what would prove a deadly diet for larger animals. Part of the strength of the frail, the strength of the insects and the other minutiae of the animal world, lies in the bewildering variety of their diet. Because their feeding habits are so varied, because the amounts of food they require are so small, because some of them-like the mayfly and the great American silk moths-live without eating during their adult periods, such creatures are able to endure privations that would kill far larger and far stronger animals.

Between a thumb and forefinger we can crush a ladybug or a butterfly. We are giants in comparison. Yet, in numerous ways, the frailer, smaller creatures of the earth possess other, special kinds of strength. They survive extreme and sudden changes in temperature and air pressure. They retain life in spite of great injuries. They reproduce with a fertility unequalled among larger animals. They are uninjured by long falls. And they possess the strength of senses that in many are specialized and abnormally keen.

Katydids can hear up to 45,000 cycles per second. This is far above the range of the human ear. Honeybees can see ultra-violet light, invisible to our eyes. That scourge of the tree-boring Tremex larva, the ichneumon fly, Megarhyssa Iunator, can smell its prey through as much as two inches of solid wood. And laboratory researches have shown that the legs of a monarch butterfly are 200 times as sensitive as the human tongue in the detection of sweets. The lowly bedbug has such an amazingly acute sense of temperature that it can detect a difference as slight as one degree Centigrade. Many of the ground-runners, such as ants and wolf spiders, are particularly sensitive to vibrations.

In The Naturalist in La Plata, W. H. Hudson tells of seeing a large, grayish, wolf spider running along beside him as he was riding across the pampas of Argentina. He struck at it with his whip. As the lash bit into the earth a few inches from it, the wolf spider leaped upon it and ran along the whip toward the rider. Dr. Willis J. Gertsch, spider authority at the American Museum of Natural History, not long ago gave me an explanation for this surprising reaction of the spider. All wolf spiders are sensitive to vibrations in the ground. Tap a pair of small forceps on the sand when a wolf spider is near and it will immediately run toward the spot. This exceeding alertness of the Lycosids aids them in detecting the presence of their prey. Thus it was not any intention of attacking the rider that caused Hudson's spider to leap upon the whip; it was the vibrations produced by the lash as it struck the ground nearby.

Another curious example of a creature highly sensitive to earth tremors was related to me, not long ago, by one of the scientists of the U. S. Bureau of Entomology. When his yard, one summer, became infested with moles, a friend in Washington, D. C., suggested a singular remedy. The scheme, which he tried, was to whittle out a number of small wooden propellers with one blade slightly longer than the other. These were mounted near the top of sticks that were thrust into the ground. The breeze, whirling the unbalanced windmills, produced a constant vibration that was carried down the sticks to the earth. Within a few weeks, the scientist told me, all the moles had left his yard.

Fifty feet or so north of the tree where the red mite fell from the leaves, seventeen sunflower stalks bear their great flat flowers rimmed by petals the color of rich butter. As thick as dust on the back of these petals, and on the under side of leaves of the plants as well, are colonies of minute insects. The largest of the winged adults are hardly three-sixteenths of an inch in length. I move my pocket magnifying glass above them and they expand into delicately formed, fantastically

beautiful little creatures. The veins of their oddly shaped wings are thickened so they seem formed of dainty lace. Curving plates, extending out from either side of the body in front of the wings, are similarly marked. These most beautiful of all the tiny creatures that drink the sap of my Insect Garden plants are the lace bugs, Corythuca arcuate.

I swing my glass away and the lace bugs return to their minute forms once more. They seem so small, so frail, so filmy; yet these delicate-appearing creatures are able to endure temperatures that would bring death by freezing to far larger, stronger animals. Hidden under bark and in fallen trees, some lace bugs overwinter in the adult form. This ability to endure great extremes of temperature is an important part in providing the strength of the frail.


One winter, a dozen Polistes paper-making wasps hibernated amid trash at the bottom of a blue box that was often covered with ice and snow at my Insect Garden. On a day of thaw, in February, I found them moving sluggishly about. When it turned cold again, they clung in position without moving. Thus they bridged the gap from fall to spring. High in the Rockies, small butterflies live through sleet storms, hiding under rocks until, a few days later, warmer weather melts the ice and they can fly about the slopes once more. En tomolo gists have noticed that such mountain insects are usually dark in color. This enables them to absorb a maximum of heat from the sun's rays. Fish, incidentally, often display amazing immunity to freezing. Certain species may be frozen in solid ice for weeks without injury. I have heard of fish being jerked from the water in the far North, when the temperature stood at forty-five degrees below zero, and being frozen stiff in the open air. Weeks later, after hanging like pieces of wood outside a cabin, they have revived when brought indoors for cooking.

Every fall, I am surprised to observe frail gnats, creatures so small, so light, so fragile that we watch them, as Keats says, "borne aloft or sinking as the light wind lives or dies." I am surprised to see these insects among the last abroad. In spite of their seeming weakness, they have a hardiness that enables them to keep active far into the harsh, later days of autumn.

Other small creatures, water striders, snow fleas, tiny spiders, are out on mild days even in midwinter. In his classic experiments with fruit flies, Dr. Frank E. Lutz showed they exhibit unbelievable resistance when subjected to sudden changes and physical strains such as they would never meet in normal life. He reduced the air pressure within a bell jar until it was equivalent to that seventeen miles and more above sea level. Twenty-four times in four hours, ten flies were subjected to this rarefied atmosphere, alternating with normal sea-level pressure. Yet two of the flies lived and bred afterwards.

One winter, an oak tree near my Insect Garden was cut down for firewood. The interior of its trunk was riddled with the galleries of carpenter ants. I brought home some of the insects, which I found huddled together in hibernation, and placed them under a desk lamp. The smallest ants were the first to revive. This is something that I might have expected, because the smaller the creature the greater the surface area in proportion to the body bulk. This fact accounts for another feature of the strength of the little. They can sustain great falls without suffering the slightest injury.

An ant can fall from the top of a skyscraper and land unharmed; cicada nymphs, hatching from eggs laid in twigs of trees, simply let go and are buoyed up by the air as they fall to the ground. The red mite that started this train of thought ran about the page of my notebook as soon as it struck the paper. Its fall for a distance many thousands of times its own height was taken as a matter of course. A man falling from four or five times his height may be crippled or killed. As size increases, the proportion of body mass to surface-area increases. Thus it is that the smallest animals are cold-blooded, the largest warm-blooded. The greater the surface area in proportion to mass, the more rapidly body-heat is dissipated. We, with a smaller proportion of surface to body mass, can be warm-blooded. The insect cannot. But the condition that makes this impossible does make possible its escape from death or injury when it falls from a height.


The mouse, one of the smallest of the warm-blooded animals, lives near the dividing line. It can be warm-blooded, and, at the same time, its surface area is proportionately large enough to slow down its speed in a long fall.

In the heart of New York City, near Radio City, there is a vacant corner lot with a high wire fence on two sides and the brick walls of buildings on the other two sides. Here, one day, a friend of mine saw a dozen men and women peering through the mesh of the wire fence watching something inside. In the corner where the brick walls met, a cat had dis-covered a mouse hidden beneath a mass of windblown papers. It would pounce first in one place then in another as the mouse scurried about under the papers. Finally, its quarry reached the nearest wall and began, climbing straight up the face of this precipice of brick.

While the cat waited below, and the people watched outside the fence, the mouse pulled itself higher and higher. Mounting upward brick by brick, it moved more slowly, searching for claw-holds. It was more than two stories above the ground when it lost its footing and plunged downward. To everyone's open-mouthed amazement, instead of lying stunned or dead when it struck the ground, the mouse scampered off and later made good its escape, much to the pleasure of many observers.

At Cornell University, another mouse sustained an even more spectacular fall. Within a few days of giving birth to a litter of young, a mother white mouse fell three stories from the roof of a building to a concrete walk below. She not only escaped death but later gave birth to a full litter of uninjured and normal baby mice. There is factual basis for the old saying that a mouse can fall down a mine-shaft unharmed while a donkey will be reduced to a grease-spot.

A fit companion for these mice is a pet tree frog that lived in a room on the tenth floor of an apartment house in Philadelphia. One summer day, by mistake, the frog leaped out of an open window. It found itself in thin air eighty feet above the ground. A few minutes later, it was discovered hopping about on the ground below with no more serious injuries than two broken toes.


Among the insects, injuries that would bring instant death to the larger animals are sometimes-temporarily, at least-almost ignored. A conehead grasshopper, with its head picked off by a chicken, kept on stridulating, continuing the music produced by its wings. A male praying mantis, hours after it had been decapitated, reared up and lifted its wings in the so-called specter pose when it was touched. A female of the silk moth, Bombyx mori, will continue laying its eggs even after its head has been severed from its body. I have seen an ant, with its entire abdomen gone, running along as though possessed of a normal body. Many young insects, if they lose a leg, simply grow another one. Monarchs sometimes fly about my garden in fall with wings tattered to shreds. Injuries of many kinds, injuries that would be mortal to animals of far greater physical strength, are often a matter of relative unconcern for the small and the frail. This, too, is part of their strength, Nature's endowment to assure perpetuation of the species.

But above everything else, above their ability to withstand long falls, severe injuries, extreme changes in temperature and air-pressure, above their amazing powers of digestion and the variety of their menu, above the benefits of their specialized and abnormally keen senses, there is another factor in the strength of the frail. This is their incredible fertility, the rapidity with which they reproduce. It reaches its peak in the smaller, weaker, the most defenseless of the insects.

The green flood of the plant lice, the emerging clouds of the mayflies, the devouring hosts of the locusts-these are symbolic of insect fertility. Two summers ago, so vast were the swarms of mayflies along the shore of one eastern lake that railway trains were stalled and traffic disrupted. Not only are numbers vast among the small, frail creatures of the earth, but the wheel of life whirls with added swiftness. Generation follows generation in rapid succession. Because of this, evolution is speeded up, the smaller creatures are better fitted to adapt themselves to meet the changing conditions of life. Thus, in numerous ways, advantages offset the physical weakness, the individual insignificance, of Earth's smallest animals. This is Nature's scheme, intricate and ever fascinating to those who know the wild.