Indirect Use as Food.--Just as plants form the food of animals, so some
animals are food for others. Man may make use of such food directly or
indirectly. Many mollusks, as the barnacle and mussel, are eaten by fishes.
Other fish live upon tiny organisms, water fleas and other small
crustaceans. These in turn feed upon still smaller animals, and we may go
back and back until finally we come to the Protozoa and one-celled water
plants as an ultimate source of food.
Direct Use as Food. Lower Forms.--The forms of life lower than the
Crustacea are of little use directly as food, although the Chinese are very
fond of one of the Echinoderms, a holothurian.
[Illustration: North American lobster. This specimen, preserved at the U.
S. Fish Commission at Woods Hole, was of unusual size and weighed over
twenty pounds.]
Crustacea as Food.--Crustaceans, however, are of considerable value for
food, the lobster fisheries in particular being of importance. The lobster
is highly esteemed as food, and is rapidly disappearing from our coasts as
the result of overfishing. Between twenty and thirty million are yearly
taken on the North Atlantic coast. This means a value at present prices of
about $15,000,000. Laws have been enacted in New York and other states
against overfishing. Egg-carrying lobsters must be returned to the water;
all smaller than six to nine inches in length (the law varies in different
states) must be put back; other restrictions are placed upon the taking of
the animals, in hope of saving the race from extinction. Some states now
hatch and care for the young for a period of time; the United States Bureau
of Fisheries is also doing much good work, in the hope of restocking to
some extent the now almost depleted waters.
Several other common crustaceans are near relatives of the crayfish. Among
them are the shrimp and prawn, thin-shelled, active crustaceans common
along our eastern coast. In spite of the fact that they form a large part
of the food supply of many marine animals, especially fish, they do not
appear to be decreasing in numbers. They are also used as food by man, the
shrimp fisheries in this country aggregating over $1,000,000 yearly.
[Illustration: The edible blue crab. (From a photograph loaned by the
American Museum of Natural History.)]
Another edible crustacean of considerable economic importance is the blue
crab. Crabs are found inhabiting muddy bottoms; in such localities they are
caught in great numbers in nets or traps baited with decaying meat. They
are, indeed, among our most valuable sea scavengers, although they are
carnivorous hunters as well. The young crabs differ considerably in form
from the adult. They undergo a complete _metamorphosis_ (change of form).
Immediately after molting or shedding of the outer shell in order to grow
larger, crabs are greatly desired by man as an article of food. They are
then known as "shedders," or soft-shelled crabs.
[Illustration: The oyster.]
Mollusks as Food.--Oysters are never found in muddy localities, for in such
places they would be quickly smothered by the sediment in the water. They
are found in nature clinging to stones or on shells or other objects which
project a little above the bottom. Here food is abundant and oxygen is
obtained from the water surrounding them. Hence oyster raisers throw oyster
shells into the water and the young oysters attach themselves.
In some parts of Europe and this country where oysters are raised
artificially, stakes or brush are sunk in shallow water so that the young
oyster, which is at first free-swimming, may escape the danger of
smothering on the bottom. After the oysters are a year or two old, they are
taken up and put down in deeper water as seed oysters. At the age of three
and four years they are ready for the market.
The oyster industry is one of the most profitable of our fisheries. Nearly
$15,000,000 a year has been derived during the last decade from such
sources. Hundreds of boats and thousands of men are engaged in dredging for
oysters. Three of the most important of our oyster grounds are Long Island
Sound, Narragansett Bay, and Chesapeake Bay.
[Illustration: This diagram shows how cases of intestinal disease (typhoid
and diarrhoea) have been traced to oysters from a locality where they were
"fattened" in water contaminated with sewage. (Loaned by American Museum of
Natural History.)]
Sometimes oysters are artificially "fattened" by placing them on beds near
the mouths of fresh-water streams. Too often these streams are the bearers
of much sewage, and the oyster, which lives on microscopic organisms, takes
in a number of bacteria with other food. Thus a person might become
infected with the typhoid bacillus by eating raw oysters. State and city
supervision of the oyster industry makes this possibility very much less
than it was a few years ago, as careful bacteriological analysis of the
surrounding water is constantly made by competent experts.
Clams.--Other bivalve mollusks used for food are clams and scallops. Two
species of the former are known to New Yorkers, one as the "round," another
as the "long" or "soft-shelled" clams. The former (_Venus mercenaria_) was
called by the Indians "quahog," and is still so called in the Eastern
states. The blue area of its shell was used by the Indians to make wampum,
or money. The quahog is now extensively used as food. The "long" clam (_Mya
arenaria_) is considered better eating by the inhabitants of Massachusetts
and Rhode Island. This clam was highly prized as food by the Indians. The
clam industries of the eastern coast aggregate nearly $1,000,000 a year.
The dredging for scallops, another molluscan delicacy, forms an important
industry along certain parts of the eastern coast.
[Illustration: Salmon leaping a fall on their way to their spawning beds.
(Photographed by Dr. John A. Sampson.)]
Fish as Food.--Fish are used as food the world over. From very early times
the herring were pursued by the Norsemen. Fresh-water fish, such as
whitefish, perch, pickerel, pike, and the various members of the trout
family, are esteemed food and, especially in the Great Lake region, form
important fisheries. But by far the most important food fishes are those
which are taken in salt water. Here we have two types of fisheries, those
where the fish comes up a river to spawn, as the salmon, sturgeon, or shad,
and those in which fishes are taken on their feeding grounds in the open
ocean. Herring are the world's most important catch, though not in this
country. Here the salmon of the western coast is taken to the value of over
$13,000,000 a year. Cod fishing also forms an important industry; over 7000
men being employed and over $2,000,000 of codfish being taken each year in
this country.
[Illustration: Globe Fisheries.]
Hundreds of other species of fish are used as food, the fish that is
nearest at hand being often the cheapest and best. Why, for example, is the
flounder so cheap in the New York markets? In what waters are the cod and
herring fisheries, sardine, oyster, sponge, pearl oyster? (See chart on
page 201.)
Amphibia and Reptiles as Food.--Frogs' legs are esteemed a delicacy.
Certain reptiles are used as food by people of other nationalities, the
Iguana, a Mexican lizard, being an example. Many of the sea-water turtles
are of large size, the leatherback and the green turtle often weighing six
hundred to seven hundred pounds each. The flesh of the green turtle and
especially of the diamond-back terrapin, an animal found in the salt
marshes along our southeastern coast, is highly esteemed as food.
Unfortunately for the preservation of the species, these animals are
usually taken during the breeding season when they go to sandy beaches to
lay their eggs.
Birds as Food.--Birds, both wild and domesticated, form part of our food
supply. Unfortunately our wild game birds are disappearing so fast that we
should not consider them as a source of food. Our domestic fowls, turkey,
ducks, etc., form an important food supply and poultry farms give lucrative
employment to many people. Eggs of domesticated birds are of great
importance as food, and egg albumin is used for other purposes,--clarifying
sugars, coating photographic papers, etc.
Mammals as Food.--When we consider the amount of wealth invested in cattle
and other domesticated animals bred and used for food in the United States,
we see the great economic importance of mammals. The United States,
Argentina, and Australia are the greatest producers of cattle. In this
country hogs are largely raised for food. They are used fresh, salted,
smoked as ham and bacon, and pickled. Sheep, which are raised in great
quantities in Australia, Argentina, Russia, Uruguay, and this country, are
one of the world's greatest meat supplies.
Goats, deer, many larger game animals, seals, walruses, etc., give food to
people who live in parts of the earth that are less densely populated.
Domesticated Animals.-- When man emerged from his savage state on the
earth, one of the first signs of the beginning of civilization was the
domestication of animals. The dog, the cow, sheep, and especially the
horse, mark epochs in the advance of civilization. Beasts of burden are
used the world over, horses almost all over the world, certain cattle, as
the water buffalo, in tropical Malaysia; camels, goats, and the llama are
also used as draft animals in some other countries.
[Illustration: Feeding silkworms. The caterpillars are the white objects in
the trays.]
Man's wealth in many parts of the world is estimated in terms of his cattle
or herds of sheep. So many products come from these sources that a long
list might be given, such as meats, milk, butter, cheese, wool, or other
body coverings, leather, skins, and hides used for other purposes. Great
industries are directly dependent upon our domesticated animals, as the
making of shoes, the manufacture of woolen cloth, the tanning industry, and
many others.
Uses for Clothing.--The manufacture of silk is due to the production of raw
silk by the silkworm, the caterpillar of a moth. It lives upon the mulberry
and makes a cocoon from which the silk is wound. The Chinese silkworm is
now raised to a slight extent in southern California. China, Japan, Italy,
and France, because of cheaper labor, are the most successful silk-raising
countries.
The use of wool gives rise to many great industries. After the wool is cut
from the sheep, it has to be washed and scoured to get out the dirt and
grease. This wool fat or lanoline is used in making soap and ointments. The
wool is next "carded," the fibers being interwoven by the fine teeth of the
carding machine or "combed," the fibers here being pulled out parallel to
each other. Carded wool becomes woolen goods; combed wool, worsted goods.
The wastes are also utilized, being mixed with "shoddy" (wool from cloth
cuttings or rags) to make woolen goods of a cheap grade.
Goat hair, especially that of the Angora and the Cashmere goat, has much
use in the clothing industries. Camel's hair and alpaca are also used.
[Illustration: Polar bear, a fur-bearing mammal which is rapidly being
exterminated. Why?]
Fur.--The furs of many domesticated and wild animals are of importance. The
Carnivora as a group are of much economic importance as the source of most
of our fur. The fur seal fisheries alone amount to many millions of dollars
annually. Otters, skunks, sables, weasels, foxes, and minks are of
considerable importance as fur producers. Even cats are now used for fur,
usually masquerading under some other name. The fur of the beaver, one of
the largest of the rodents or gnawing mammals, is of considerable value, as
are the coats of the chinchilla, muskrats, squirrels, and other rodents.
The fur of the rabbit and nutria are used in the manufacture of felt hats.
The quills of the porcupines (greatly developed and stiffened hairs) have a
slight commercial value.
Conservation of Fur-bearing Animals Needed.--As time goes on and the furs
of wild animals become scarcer and scarcer through overkilling, we find the
need for protection and conservation of many of these fast-vanishing wild
forms more and more imperative. Already breeding of some fur-bearing
animals has been tried with success, and cheap substitutes for wild animal
skins are coming more and more into the markets. Black-fox breeding has
been tried successfully in Prince Edward Island, Canada, $2500 to $3000
being given for a single skin. Skunk, marten, and mink are also being bred
for the market. Game preserves in this country and Canada are also helping
to preserve our wild fur-bearing animals.
Animal Oils.--Whale oil, obtained from the fat or "blubber" of whales, is
used extensively for lubricating. Neat's-foot oil comes from the feet of
cattle and is also used in lubrication. Tallow and lard, two fats from
cattle, sheep, and pigs, have so many well-known uses that comment is
unnecessary. Cod-liver oil is used medically and is well known. But it is
not so widely known that a fish called the menhaden or "moss bunkers" of
the Atlantic coast produces over 3,000,000 gallons of oil every year and is
being rapidly exterminated in consequence.
Hides, Horns, Hoofs, etc.--Leathers, from cattle, horses, sheep, and goats,
are used everywhere. Leather manufacture is one of the great industries of
the Eastern states, hundreds of millions of dollars being invested in its
manufacturing plants. Horns and bones are utilized for making combs,
buttons, handles for brushes, etc. Glue is made from the animal matter in
bones. Ivory, obtained from elephant, walrus, and other tusks, forms a
valuable commercial product. It is largely used for knife handles, piano
keys, combs, etc.
Perfumes.--The musk deer, musk ox, and muskrat furnish a valuable perfume
called musk. Civet cats also give us a somewhat similar perfume. Ambergris,
a basis for delicate perfumes, comes from the intestines of the sperm
whale.
Protozoa.--The Protozoa have played an important part in rock building. The
chalk beds of Kansas and other chalk formations are made up to a large
extent of the tiny skeletons of _Protozoa_, called _Foraminifera_. Some
limestone rocks are also composed in large part of such skeletons. The
skeletons of some species are used to make a polishing powder.
Sponges.--The sponges of commerce have the skeleton composed of tough
fibers of material somewhat like that of cow's horn. This fiber is elastic
and has the power of absorbing water. In a living state, the horny fiber
sponge is a dark-colored fleshy mass, usually found attached to rocks. The
warm waters of the Mediterranean Sea and the West Indies furnish most of
our sponges. The sponges are pulled up from their resting place on the
bottom, by means of long-handled rakes operated by men in boats or are
secured by divers. They are then spread out on the shore in the sun, and
the living tissues allowed to decay; then after treatment consisting of
beating, bleaching, and trimming, the bath sponge is ready for the market.
Some forms of coral are of commercial value. The red coral of the
Mediterranean Sea is the best example.
[Illustration: In some countries little metal images of Buddha are placed
within the shells of living pearl oysters or clams. Over these the mantle
of the animal secretes a layer of mother of pearl as is shown in the
picture.]
Pearls and Mother of Pearl.--Pearls are prized the world over. It is a
well-known fact that even in this country pearls of some value are
sometimes found within the shells of the fresh-water mussel and the oyster.
Most of the finest, however, come from the waters around Ceylon. If a pearl
is cut open and examined carefully, it is found to be a deposit of the
mother-of-pearl layer of the shell around some central structure. It has
been believed that any foreign substance, as a grain of sand, might
irritate the mantle at a given point, thus stimulating it to secrete around
the substance. It now seems likely that most perfect pearls are due to the
growth within the mantle of the clam or oyster of certain parasites, stages
in the development of a flukeworm. The irritation thus set up in the tissue
causes mother of pearl to be deposited around the source of irritation,
with the subsequent formation of a pearl.
The pearl-button industry in this country is largely dependent upon the
fresh-water mussel, the shells of which are used. This mussel is being so
rapidly depleted that the national government is working out a means of
artificial propagation of these animals.
Honey and Wax.--Honeybees[29] are kept in hives. A colony consists of a
queen, a female who lays the eggs for the colony, the drones, whose duty it
is to fertilize the eggs, and the workers.
Footnote 29: Their daily life may be easily watched in the
schoolroom, by means of one of the many good and cheap
observation hives now made to be placed in a window frame.
Directions for making a small observation hive for school
work can be found in Hodge, _Nature Study and Life_, Chap.
XIV. Bulletin No. 1, U. S. Department of Agriculture,
entitled _The Honey Bee_, by Frank Benton, is valuable for
the amateur beekeeper. It may be obtained for twenty-five
cents from the Superintendent of Documents, Union Building,
Washington, D.C.
[Illustration: Cells of honeycomb, queen cell on right at bottom.]
The cells of the comb are built by the workers out of wax secreted from the
under surface of their bodies. The wax is cut off in thin plates by means
of the wax shears between the two last joints of the hind legs. These cells
are used to place the eggs of the queen in, one egg to each cell, and the
young are hatched after three days, to begin life as footless white grubs.
The young are fed for several days, then shut up in the cells and allowed
to form pupae. Eventually they break their cells and take their place as
workers in the hive, first as nurses for the young and later as pollen
gatherers and honey makers.
We have already seen (pages 37 to 39) that the honeybee gathers nectar,
which she swallows, keeping the fluid in her crop until her return to the
hive. Here it is forced out into cells of the comb. It is now thinner than
what we call honey. To thicken it, the bees swarm over the open cells,
moving their wings very rapidly, thus evaporating some of the water. A hive
of bees have been known to make over thirty-one pounds of honey in a single
day, although the average is very much less than this. It is estimated from
twenty to thirty millions of dollars' worth of honey and wax are produced
each year in this country.
Cochineal and Lac.--Among other products of insect origin is cochineal, a
red coloring matter, which consists of the dried bodies of a tiny insect,
one of the plant lice which lives on the cactus plants in Mexico and
Central America. The lac insect, another one of the plant lice, feeds on
the juices of certain trees in India and pours out a substance from its
body which after treatment forms shellac. Shellac is of much use as a basis
for varnish.
Gall Insects.--Oak galls, growths caused by the sting of wasp-like insects,
give us products used in ink making, in tanning, and in making pyrogallic
acid which is much used in developing photographs.
Insects destroy Harmful Plants or Animals.--Some forms of animal life are
of great importance because of their destruction of harmful plants or
animals.
[Illustration: An insect friend of man. An ichneumon fly boring in a tree
to lay its eggs in the burrow of a boring insect harmful to that tree.]
A near relative of the bee, called the ichneumon fly, does man indirectly
considerable good because of its habit of laying its eggs and rearing the
young in the bodies of caterpillars which are harmful to vegetation. Some
of the ichneumons even bore into trees in order to deposit their eggs in
the larvae of wood-boring insects. It is safe to say that the ichneumons
save millions of dollars yearly to this country.
Several beetles are of value to man. Most important of these is the natural
enemy of the orange-tree scale, the ladybug, or ladybird beetle. In New
York state it may often be found feeding upon the plant lice, or aphids,
which live on rosebushes. The carrion beetles and many water beetles act as
scavengers. The sexton beetles bury dead carcasses of animals. Ants in
tropical countries are particularly useful as scavengers.
Insects, besides pollinating flowers, often do a service by eating harmful
weeds. Thus many harmful plants are kept in check. We have noted that they
spin silk, thus forming clothing; that in many cases they are preyed upon,
and that they supply an enormous multitude of birds, fishes, and other
animals with food.
[Illustration: The common toad, an insect eater.]
Use of the Toad.--The toad is of great economic importance to man because
of its diet. No less than eighty-three species of insects, mostly
injurious, have been proved to enter into the dietary. A toad has been
observed to snap up one hundred and twenty-eight flies in half an hour.
Thus at a low estimate it could easily destroy one hundred insects during a
day and do an immense service to the garden during the summer. It has been
estimated by Kirkland that a single toad may, on account of the cutworms
which it kills, be worth $19.88 each season it lives, if the damage done by
each cutworm be estimated at only one cent. Toads also feed upon slugs and
other garden pests.
Birds eat Insects.--The food of birds makes them of the greatest economic
importance to our country. This is because of the relation of insects to
agriculture. A large part of the diet of most of our native birds includes
insects harmful to vegetation. Investigations undertaken by the United
States Department of Agriculture (Division of Biological Survey) show that
a surprisingly large number of birds once believed to harm crops really
perform a service by killing injurious insects. Even the much maligned crow
lives to some extent upon insects. Swallows in the Southern states kill the
cotton-boll weevil, one of our worst insect pests. Our earliest visitor,
the bluebird, subsists largely on injurious insects, as do woodpeckers,
cuckoos, kingbirds, and many others. The robin, whose presence in the
cherry tree we resent, during the rest of the summer does much good by
feeding upon noxious insects. Birds use the food substances which are most
abundant around them at the time.[30]
Footnote 30: The following quotation from I. P. Trimble, _A
Treatise on the Insect Enemies of Fruit and Shade Trees_,
bears out this statement: "On the fifth of May, 1864, ...
seven different birds ... had been feeding freely upon small
beetles.... There was a great flight of beetles that day;
the atmosphere was teeming with them. A few days after, the
air was filled with Ephemera flies, and the same species of
birds were then feeding upon them."
During the outbreak of Rocky Mountain locusts in Nebraska in
1874-1877, Professor Samuel Aughey saw a long-billed marsh
wren carry thirty locusts to her young in an hour. At this
rate, for seven hours a day, a brood would consume 210
locusts per day, and the passerine birds of the eastern half
of Nebraska, allowing only twenty broods to the square mile,
would destroy daily 162,771,000 of the pests. The average
locust weighs about fifteen grains, and is capable each day
of consuming its own weight of standing forage crops, which
at $10 per ton would be worth $1743.26. This case may serve
as an illustration of the vast good that is done every year
by the destruction of insect pests fed to nestling birds.
And it should be remembered that the nesting season is also
that when the destruction of injurious insects is most
needed; that is, at the period of greatest agricultural
activity and before the parasitic insects can be depended on
to reduce the pests. The encouragement of birds to nest on
the farm and the discouragement of nest robbing are
therefore more than mere matters of sentiment; they return
an actual cash equivalent, and have a definite bearing on
the success or failure of the crops.--_Year Book of the
Department of Agriculture._
[Illustration: Food of some common birds. Which of the above birds should
be protected by man and why?]
Birds eat Weed Seeds.--Not only do birds aid man in his battles with
destructive insects, but seed-eating birds eat the seeds of weeds. Our
native sparrows (not the English sparrow), the mourning dove, bobwhite, and
other birds feed largely upon the seeds of many of our common weeds. This
fact alone is sufficient to make birds of vast economic importance.
Not all birds are seed or insect feeders. Some, as the cormorants, ospreys,
gulls, and terns, are active fishers. Near large cities gulls especially
act as scavengers, destroying much floating garbage that otherwise might be
washed ashore to become a menace to health. The vultures of India and
semitropical countries are of immense value as scavengers. Birds of prey
(owls) eat living mammals, including many rodents; for example, field mice,
rats, and other pests.
Extermination of our Native Birds.--Within our own times we have witnessed
the almost total extermination of some species of our native birds. The
American passenger pigeon, once very abundant in the Middle West, is now
extinct. Audubon, the greatest of all American bird lovers, gives a graphic
account of the migration of a flock of these birds. So numerous were they
that when the flock rose in the air the sun was darkened, and at night the
weight of the roosting birds broke down large branches of the trees in
which they rested. To-day not a single wild specimen of this pigeon can be
found, because they were slaughtered by the hundreds of thousands during
the breeding season. The wholesale killing of the snowy egret to furnish
ornaments for ladies' headwear is another example of the improvidence of
our fellow-countrymen. Charles Dudley Warner said, "Feathers do not improve
the appearance of an ugly woman, and a pretty woman needs no such aid."
Wholesale killing for plumage, eggs, and food, and, alas, often for mere
sport, has reduced the number of our birds more than one half in thirty
states and territories within the past fifteen years. Every crusade against
indiscriminate killing of our native birds should be welcomed by all
thinking Americans. The recent McLane bill which aims at the protection of
migrating birds and the bird-protecting clause of the recently passed
tariff bill shows that this country is awaking to the value of her bird
life. Without the birds the farmer would have a hopeless fight against
insect pests. The effect of killing native birds is now well seen in Italy
and Japan, where insects are increasing and do greater damage each year to
crops and trees.
Of the eight hundred or more species of birds in the United States, only
six species of hawks (Cooper's and the sharp-shinned hawk in particular),
and the great horned owl, which prey upon useful birds; the sapsucker,
which kills or injures many trees because of its fondness for the growing
layer of the tree; the bobolink, which destroys yearly $2,000,000 worth of
rice in the South; the crow, which feeds on crops as well as insects; and
the English sparrow, may be considered as enemies of man.
The English Sparrow.--The English sparrow is an example of a bird
introduced for the purpose of insect destruction, that has done great harm
because of its relation to our native birds. Introduced at Brooklyn in 1850
for the purpose of exterminating the cankerworm, it soon abandoned an
insect diet and has driven out most of our native insect feeders.
Investigations by the United States Department of Agriculture have shown
that in the country these birds and their young feed to a large extent upon
grain, thus showing them to be injurious to agriculture. Dirty and very
prolific, it already has worked its way from the East as far as the Pacific
coast. In this area the bluebird, song sparrow, and yellowbird have all
been forced to give way, as well as many larger birds of great economic
value and beauty. The English sparrow has become a pest especially in our
cities, and should be exterminated in order to save our native birds. It is
feared in some quarters that the English starling which has recently been
introduced into this country may in time prove a pest as formidable as the
English sparrow.
[Illustration: This shows how some snakes (constrictors) kill and eat their
prey. (Series photographed by C. W. Beebe and Clarence Halter.)]
Food of Snakes.--Probably the most disliked and feared of all animals are
the snakes. This feeling, however, is rarely deserved, for, on the whole,
our common snakes are beneficial to man. The black snake and the milk snake
feed largely on injurious rodents (rats, mice, etc.), the pretty green
snake eats injurious insects, and the little DeKay snake feeds partially on
slugs. If it were not that the rattlesnake and the copperhead are venomous,
they also could be said to be useful, for they live on English sparrows,
rats, mice, moles, and rabbits.
Food of Herbivorous Animals.--We must not forget that other animals besides
insects and birds help to keep down the rapidly growing weeds. Herbivorous
animals the world over destroy, besides the grass which they eat, untold
multitudes of weeds, which, if unchecked, would drive out the useful
occupants of the pasture, the grasses and grains.