Instances of small birds, lizards and mice being eaten have been
reported, probably due to mistaken observations. There is no question
that mature individuals of several species can handle any caterpillar,
grasshopper, cockroach or other large insect that comes within its
range. Their appetite is enormous. An adult mantid has been known to
eat ten cockroaches in less than three hours. Bees and wasps usually
have no terrors for the predators, although occasionally a mantid is
stung while trying to catch a wasp and gives evidence of the injury.
Sometimes the mantid’s front legs are held in a posture of sparring,
rather than of prayer. More than once the sight of one of these insects
“sparring” with an English sparrow or some other small animal has
attracted a crowd on a city street and gotten paragraphs in the local
newspapers.
The mantid usually waits motionless until its prey comes within reach
but sometimes, supposedly when very hungry, it may stalk another
insect. Sometimes the victim is touched lightly with the antennae
before the front legs flash forward and make the capture.
These insects have developed considerable camouflage. Some tropical
species look like flowers, their colors blending with those of foliage.
One species varies in color from white to pale pink and has the
practise of crouching among certain blossoms, the petals of which its
legs and other body parts resemble. Others have arranged themselves on
plants so that they look like blue flowers. Presumably bees and other
flower-loving insects thus are lured to their doom. A few tropical
mantids have developed a superficial resemblance to other insects of
the same environment which are distasteful to birds and monkeys. Some
closely resemble large ants.
There is a widespread belief that the male always is eaten by the
female after mating. Sometimes this happens, but the male never is
a willing victim and quite frequently escapes. The eggs are laid in
groups of from a dozen to about 400. They are deposited in layers in
the midst of a thick frothy liquid which soon hardens and becomes
fibrous. For the most part, each species deposits egg masses of a
distinctive shape.
On the whole, they probably are beneficial insects because the
greater part of their prey consists of species injurious to gardens.
The possibility of propagating them for the control of injurious
insects, such as Japanese beetles, has been suggested because of their
notoriously big appetites. It would, however, be impossible to restrict
them to a specific pest. They would continue to eat about every living
creature of the right size that came within reach of their claws,
including many beneficial species.
_Fireflies as Electricians_
The flashing of a field of fireflies is an expensive show. For
two generations one of the ideals of science has been to produce
artificially “cold light”—radiation confined entirely to those
wavelengths to which the retina of the human eye is sensitive without
any energy being wasted in the form of heat or invisible light. Could
the ideal be attained with the same expenditure of fuel and power as
is required for light production at present the world’s bills for
illumination would be decreased enormously.
Actually the firefly has attained this ideal in one direction. It emits
only visible light. From this point of view the firefly or any other
sort of luminescent animal is very efficient indeed. A good part of the
total radiation from any man-made source of light—or for that matter
from the sun—is invisible infrared, observable only as heat. Possibly
the firefly produces some heat in its light production but it is too
little to be measured. It is safe to say that within a tiny fraction,
100% of the radiation produced is in the visible spectrum—most of it
shorter wave lengths than those which produce the sensation of blue
light. This is by far the highest efficiency known to science.
Chemists can duplicate the process to a certain extent. Consequently
a great deal of research has been devoted to the light-emitting
mechanism, physical and chemical, of the insects. Firefly luminescence
is due to the oxidation—that is, the burning—of a chemical substance,
luciferin. This reaction, in turn, depends upon a catalyst known as
luciferase. The same phenomenon can be brought out by appropriate
mixtures of luciferin, luciferase, and oxygen in a test-tube at the
proper temperature.
All these experiments have shown that, considering the amount of oxygen
necessary, it is a very wasteful process. It is far less efficient
than most means of producing artificial light known to man—one percent
compared with the 4.54 percent of the carbon filament; 17.17 percent
of the acetylene flame, or 60 percent of the sodium arc light. To
illuminate houses or streets with firefly light would be a very
expensive procedure indeed.
Dr. N. D. Maluf of Yale University quotes a calculation that “an area
of firefly light six feet in diameter on the ceiling of a room nine
feet high would give ample illumination for reading or drawing on a
table three feet high.” This would hardly interest an illuminating
engineer. The light can, however, be used in an emergency. During the
Spanish-American War Major General W. C. Gorgas is reputed to have used
the light from a bottle of fireflies to perform an emergency operation.
The average householder would rebel at the monthly bills.
The actual light from a single firefly is very minute indeed, averaging
little more than 25 thousandths of a candle power. The combined
courtship efforts of a whole field full of the insects would hardly
light a single room enough for sewing or reading. The insect will
sometimes glow steadily with a light as low as two hundred-thousandths
of candle power intensity.
Among fireflies, flashing is essentially a courtship phenomenon, yet
there is no discernible difference between the quality of the light of
male and female insects. What actually happens is that the flash of the
female in response to the signal of the male is timed almost exactly at
a trifle over two seconds. The male is instinctively aware of this time
interval, so that he does not become confused with the signals of other
males. In a large group of the insects the flashes of the two sexes
tend to become synchronized, producing a field of light.
_The Mollusk Vampire of Hell_
Black demon of the realm of everlasting dark is Vampyrotouthis
infernalis. Most nightmarish of living animals, this “vampire of hell”
has a midnight-black body about two inches long, red-brown round face
on a head almost as large as the rest of the body, red eyes an inch in
diameter encircled by narrow bands of pinkish-orange, rows of ivory
white teeth, ten wriggling, ever-probing tentacles extending from the
head. On the sides of the neck are two powerful, flashing lights each
of which is a cluster of about 50 tiny phosphorescent nodules. The
entire body is covered with hundreds of tiny lights.
Fortunately nobody is likely to meet this horror of an
hallucination-damned maniac’s ravings on a lonely road passing a
graveyard at night. It is a mollusk, a close relative of the octopus
and the squid but belonging to neither family, which lives in abysses
of sub-tropical seas all around the world, far below the depths reached
by the most penetrating green rays of the sun. Only its relatively
small size and restricted habitat prevent it from being the most
fearsome, loathsome creature on this planet.
The “vampire” is a living fossil, survivor out of the demonic seas of
200,000,000 years ago which found shelter from the inexorable scythe
with which time mows down demons by retreating further and further into
the dark. Imprints of quite similar sea animals, probably denizens of
warm, shallow waters, have been found in English rocks.
Up to now about a hundred individuals have been taken from the deep
sea, mostly by scientific expeditions. Of these, nearly two-thirds
have come from the Atlantic off the Florida coast and near Bermuda.
There are several in the Smithsonian collections. The fantastically
terrible little mollusk was first taken in the Indian Ocean by Dr. Carl
Cuhn of the German Valdavia expedition about 75 years ago. Until quite
recently all specimens obtained have been in poor condition and there
has been considerable difficulty in classifying them. The job has been
complicated by the fact that the vampire apparently undergoes a series
of metamorphoses which have been mistaken for different species. During
the past ten years, however, they have been studied intensively by Dr.
Grace Pickford of the Bingham Oceanographic Laboratory of Yale and
their fearsome reality has been established beyond question.
Naturally, since the living animal cannot be observed, essentially
little is known of its habits and ways of life. Certainly it is a
voracious carnivore like all others of its race and preys upon every
other creature of the depths in its size range. It seems to be confined
exclusively to a depth of about 1,500 meters. This is the level of the
sea where, for some reason oceanographers are unable to fathom, the
oxygen content of the water is lowest. It goes up immediately both
above and below. The vampire, apparently, cannot stand too much oxygen.
Its eggs sink to about 2,000 meters where they reach their suspension
level. As soon as the little mollusks hatch they rise to their natural
habitat.
The vampire has powerful tentacles but its fin muscles indicate that
it is a weak swimmer. It probably lurks in the abysmal darkness for
its prey to come within reach of the probing tentacles. Even with its
enormous eyes and its many lights it hardly can distinguish moving
objects very well and presumably is not particular about what living
things it eats. Its usual victims probably are fishes and smaller
mollusks. It is unlikely that the creature has many natural enemies it
need fear. Unlike the octopuses, its nearest relations, it has no ink
sac from which to discharge a black cloud around its body for its own
concealment.
_Climbing and Flying Frogs_
A family of frogs that climb trees, burrow and are learning to fly are
the tree frogs of Mexican tropical forests. Various members of the
family are at different stages in their physical adaptation to tree
life. They constitute a striking example of evolution at work as a race
struggles to shake itself free from one environment and conquer another
despite considerable odds.
The ends of the fingers and toes of those frogs are provided with
adhesive disks by means of which the animals are able to obtain a firm
foothold on relatively smooth surfaces. These disks are used mainly
for climbing, or for clinging to foliage and limbs when jumping. One
species is both a climber and burrower. It is an extremely timid little
creature and a poor climber, but it buries itself deeply in tree
mosses. Another species, which seems as much as home on the ground
as in the trees, deposits its eggs on the upper surfaces of leaves
overhanging the water. The tadpoles, which must return to the water
for their metamorphosis into frogs, simply drop off the leaves after
they leave the eggs. Perhaps the most peculiar of the family is the
marsupial frog, Gastrotheca, all of whose young are sheltered in a
pouch on the back of the female. Some of the family lay their eggs in
nests of froth attached to leaves.
One remarkable species seems to be developing the ability to fly. Its
hind limbs are elongated for jumping and it has been known to leap
and alight without injury from a height of 140 feet. When handled it
exudes a poisonous, milky fluid which coagulates instantly, sticking to
the fingers in a disagreeable way. It has a strong odor, like that of
peaches, which causes the inside of the nose to itch. Experiments are
described in which this animal was dropped from the top of a high water
tower. It immediately spread out its limbs and, instead of dropping
vertically, sailed slowly downward and landed uninjured on the ground
about 90 feet away. Apparently it was able to get the best of gravity
after a drop of about twelve feet. From that point on, there was no
apparent acceleration in the speed of descent. A state of equilibrium
was reached. Whenever one of these frogs was thrown in the air it
invariably managed, after a violent struggle, to establish itself in a
balanced position which it could maintain, apparently without effort,
while it glided to the ground.
Within certain limits these tree frogs can change their color so
that their bodies will blend more perfectly with their surroundings.
One of the most widely distributed Mexican species seems to have an
exceptional color range. This particular creature also is notable
for its elusiveness. It exists in countless numbers, yet an explorer
may hunt for weeks without encountering a single one. Such was the
experience of the German naturalist, Hans Gadow. While wandering along
the edge of the forest he heard what seemed to be the noise of a
sawmill in the distance. As he came nearer this sound changed into a
roar like that of steam escaping from many boilers, mingled with the
sharp and piercing scream of saws. It came from a meadow containing a
shallow rainwater pool in which were tens of thousands of large, green
tree frogs. Gadow calculated that in this pool, about thirty yards
square, and in the immediate neighborhood, were more than 45,000 of the
creatures. The water of the pool was covered with their spawn—a minimum
of 100,000,000 eggs. The next morning there was not a single frog in
sight. The water had evaporated during the night and the eggs were left
to be cooked by the sun.
One of the most curious of these creatures is the banana frog, whose
habitat often is the upper side of a banana leaf. It is an extremely
elusive creature whose color undergoes considerable change without
being specifically responsive, so far has been observed, to the
intensity of light. Another curious member of the family wraps its eggs
in foamy lather and suspends the whole mass between leaves or blades of
grass over water in such a manner that the next heavy rain washes the
developing eggs or tadpoles into it. It is necessary that the tadpole
stage be passed in water. Development of means to bring this about was
necessary before the family could conquer a tree environment.
Another little frog spends its entire life in the leaf-formed cup of
a bromelia, a plant somewhat similar in appearance to a small century
plant, which grows on the branches of trees where its roots get a
precarious foothold. During the rainy season this cup becomes filled
with water. There the frog lays its eggs, which hatch as pollywogs.
Truly demonic are fantastic horned frogs of Brazil which devour other
amphibians and small mammals. The largest of them do not hesitate to
defy a human being in the mountain rain forests, their chief habitat.
They are six inches long or longer and as broad as long. Some have
horns on their eyelids and the tips of their noses. All have enormous
mouths, so that a mouse can be swallowed quite easily. When excited
they inflate their bodies like balloons and utter bull-like bellows. At
other times they are heard to cry like infants.
The horns probably serve no other purpose than to add to the ferocious
appearance of the animals. They are just hardened extensions of the
skin, entirely too soft to be of any value in combat. All species of
horned frogs are rare in collections. They seldom are seen because of
their secluded habitat and their clever camouflage. They throw loose
dirt over their damp bodies until they become practically invisible.
Rarest of the family are the pigmy horned frogs which have horns on
both eyelids and the tip of the nose, as well as a fringe of horns
around the eyes. They are beautifully marked animals.
_Mad Dog Cycles_
There may be mad dog cycles. Dogs are much more vicious in June than in
the so-called “dog-days” season of July and August.
The tiny poodle and the pekingese share with the big German police
dog and the Italian bull rank among the 10 most vicious of domestic
canines. These are some of the conclusions reached by Dr. Robert Oleson
of the U. S. Public Health Service on the basis of data about dogs in
the metropolitan New York area for 27 years.
During this period, Dr. Oleson’s study shows there were two 5-year
peaks in rabies, from 1911 to 1915, inclusive, and from 1926 to 1930.
During the first period the annual average of bites diagnosed as made
by rabies-infected animals was 233, compared with only an average of
78 for the previous three years for which records were available.
There followed a period of 10 years during which the number of rabies
cases diagnosed in biting dogs averaged only 43 a year. Starting with
1926 the curve leaped up again and in the next five years there was an
average of 288 cases a year. Then came another rapid decline.
Apparently the number of rabies cases has no relation to the number of
bites. These remained practically stationary at an average of about
3,500 from 1908 to 1926. There was a sudden jump to more than 7,000
cases in 1925, just before the start of the second rabies peak. But
since 1930 the number of bites reported has continued to go up, in the
face of rigid muzzling restrictions, until it has reached the alarming
figure of 20,000. At the same time the number of rabies cases rapidly
has gone down.
The same tendency toward the mad dog cycle has been noted in several
European countries. It may be due to an inexplicable waxing and
waning of the virulency of the rabies virus. During the peak years
extraordinary efforts were made to impound all unlicensed dogs, and the
decline of the waves may have been due to the lessening of the number
of potential rabies carriers by this means.
Contrary to general belief, dogs are getting better tempered rapidly
during dog days. The high peak of the year in bites is reached about
the middle of June. Then comes a very sharp drop, which continues
steadily as colder weather comes on.
No breed of dogs is entirely free from the biting tendency, but some
are much more prone to it than others. The mongrel doesn’t rank among
the really vicious dogs and pedigree counts for nothing. The 10 breeds,
in the order of frequency of their reported bites, are: German police,
chow, poodle, Italian bull, fox terrier, crossed chow, airedale,
pekingese and crossed German police dog.
_The Amazing Survival of the Opossum_
The opossum, sole survivor in the New World of a primitive and
very ancient family, represents an overlooked principle in
evolution—survival by endurance.
How this clumsy, persecuted animal has endured through millions of
generations in the midst of savage and hungry foes is the subject of a
revealing study by Dr. J. D. Black of the University of Kansas.
Dr. Black examined closely the skeletons of 95 opossums in the
university museum—all killed in the immediate vicinity. Thirty-nine
of them gave evidence of broken bones that had completely healed. One
specimen had suffered, and recovered from, breaks of both scapulae,
11 ribs, two broken in three places, and a badly injured spine. Still
another gave evidence of having suffered at the same time fractures of
the jaw, the scapulae, and nine ribs. Many showed evidence of ribs and
scapulae broken in several places. The ability to survive such severe
injuries—they would be fatal in any other animal either in themselves
or because the crippled condition resulting from them would make a
creature an easy prey to its enemies—illustrates the importance of the
opossum’s practice of playing dead.
The opossum represents an important stage in the evolution of
mammals—that of the marsupials, or pouch bearers. They presumably
were quite widely distributed over the earth at one time, before the
emergence of the placental type of mammals to which the human race
belongs, together with almost all other warm-blooded animals. They may
be the ancestors of the placentals or they may represent a different
line of development from the ancestral reptiles. In any event, they are
considerably nearer the type of those ancient egg-laying reptiles. They
are just a step beyond the egg-laying stage.
When the placentals arose the marsupials quickly disappeared from most
of the earth. They were not so well adapted for survival in conflict
with the more advanced, efficient type of animal. Only in Australia
did they find a haven. With a single exception, they were the only
mammals there when the continent first was discovered by white men.
This has led to the speculation that Australia was cut off from the
rest of the world before the placental races were evolved, or before
they had attained such efficiency in the ways of life as to enable them
to survive. There the marsupials, without competition, were able to
survive and differentiate into rich fauna of the continent—of which the
kangaroos are considered the most characteristic animals.
The one exception was in North and South America in the person of the
lowly opossum. All the meat-eating animals which arose around the
creature fed upon it if they could catch it. It was not very efficient
in getting away from a pursuer. It developed no effective armor, like
the shell of the armadillo or the quills of the porcupine, with which
other weak animals managed to survive. It was not even very efficient
at hiding. When man arrived on the scene with his bows and his guns,
its last havens, the treetops, lost their small measure of security.
All the cards were stacked against the survival of the opossum, but it
developed a means of its own to keep a tenacious hold on life while
far more efficient creatures—beset with new enemies and changing
climates—were forced to give up. The great mammoth herds, lords of
the earth for a million years, disappeared. The ferocious saber-tooth
tiger and the great cave bear expired by the roadside in the race of
evolution. But the poor opossum had discovered the important principle
that the meek shall inherit the earth—or, at least, be allowed to live
in it. It became the great pain endurer and lived by submitting and
gritting its teeth. It didn’t fight nor hide. It merely suffered and
learned how to endure suffering. This supreme ability of the opossum to
recover from injuries goes a long way toward explaining its survival.
The opossum thus appears to be the prototype of a familiar class of
men and women. They are frequently encountered. As children they have
almost every conceivable disease. Their adolescence is a continuous
succession of broken bones. Their parents despair of raising them.
When they come to adult life the story is much the same. They suffer a
constant stream of misfortunes, physical and otherwise. Physicians are
amazed at their recoveries. And they often survive into the 80s and 90s
of life while the healthy, fortunate individuals with whom they started
out are left behind in the prime of life—victims of pneumonia, heart
disease or accident. When the latter die the news comes as a surprise
to their acquaintances who cannot understand how the strong die and the
weak survive. They ponder over the paradox that strength is weakness
and weakness strength. The ancient opossum might explain that paradox
if it had the means to express itself.
_Mammal Prototypes of the “Mermaid”_
The prototypes of the “mermaids” of legend are among the least known
of all animals to naturalists because of their underwater habitat and
their secretive habits. They are the manatees of the Caribbean region
and the dugongs of the Indian Ocean. They constitute the only remaining
species of the serenia, or moon creatures, distant relatives of the
elephant. Both have a somewhat human facial appearance. They feed
standing upright in the water, their flippers held out before them like
arms. Sometimes the females hold their calves in these flippers. Seen
from a distance, they have a curiously human appearance, which may
account for the many reports of mermaids and mermen.
This is especially true of the dugong—a creature of the open sea,
with a white, almost hairless body. It is extremely secretive and has
almost never been captured alive. When one is washed ashore or caught
in a fisher’s net it causes superstitious fear among the natives. The
manatees are not so human in appearance and are much better known.