all the others put together. Most of them feed on plants but many eat other insects and any other animal flesh that they can attack. The lower vertebrates feed largely on insects or other animal food. The birds are divided into insectivorous and the seed-eating, though many are omnivorous. The lower mammals are chiefly carnivorous. Higher groups are often wholly herbivorous though the primates are omnivorous. All animals, from insects and crustaceans to birds and mammals, contain parasites.

The Struggle for Existence

We are accustomed to think of "natural death" as the end of a wearing-out process continued through life, that is, we have a machine in mind. In fact, no form of death is less The usual cause of death is the attack of some

common.

other organism. Well may Roosevelt write :

Civilized man now usually passes his life under conditions which eliminate the intensity of terror felt by his ancestors when death by violence was their normal end, and threatened them during every hour of the day and night. It is only in nightmares that the average dweller in civilized countries now undergoes the hideous terror which was the regular and frequent portion of his ages-vanished forefathers, and which is still an everyday incident in the lives of most wild creatures.

...

Death by violence, death by cold, death by starvation-these are the normal endings of the stately and beautiful creatures of the wilderness. The sentimentalists who prattle about the peaceful life of nature do not realize its utter mercilessness; although all they would have to do would be to look at the birds in the winter's woods, or even at the insects on a cold morning or cold evening.17

Mr. Roosevelt is entirely correct unless he wishes us to understand that the animals are not only frequently scared but have an abiding fear of death, in which case we should have to class him as a "nature-faker."

The desire to live results of necessity in what is called competition or the struggle for existence. It is the spectacular aspect of the daily round of life and is always in the foreground, attracting attention as does a fire or a fight. There is another aspect of life, however, which is quite as real and which may be of equal importance, though it is hard to compare the two for their ends are different. This second aspect grows out of coöperation in nature, and that organisms live in communities rather than as scattered individuals.

We are forced to interpret the associations of plants as due to chance rather than emotion of any sort. Nor would it be proper to assume that there is no competition in a community of plants. There are so many plants on many fields that they cannot grow and prosper as they would if half of them were removed. They compete for water, food, and sunlight. Some are killed by the competition, others just survive, some thrive but all survivors are handicapped. We can see nothing voluntary in the associations of a colony of coral polyps or oysters nor in the swarms of mosquitoes. It is not easy to tell where anything more than the chance location of birth begins to be dominant, but the ant and the bee have a form of social organization which cannot be interpreted on a basis of chance.

Animal Associations

Even in the animal associations we must not think that competition is eliminated. Insects have some habits that surprise us:

Perhaps the strangest of these is a little fly, one of the gallmidges which as a grub is found beneath the bark of trees. The grubs of this gall-midge produce a number of young within their own bodies which immediately proceed to eat their mother, and when she is but a memory they bore out of her empty skin and start life on their own account. A swift retribution overtakes them, however; for their young appear within them and they are devoured in the same way. This process of progressive mother eating continues all the winter, and at the beginning of spring the now very numerous grubs transform into adults. 18

The females of many spiders and of such insects as the praying mantis regularly devour their mates.

While it is true that some of the higher animals live in very small family groups like the gorilla, many ny of them seein to prefer the largest possible groupings. Wherever man is not abundant and food conditions are favorable, animals gather in enormous flocks.

Even with the naked eye we could see hundreds of yellowish forms swimming in the desert mirage. Wild asses, without a doubt, but never before had I seen a herd so vast. They were massed in three dense groups on the valley floor, and for miles the horizon was dotted with stragglers. We counted a block of two hundred and could estimate fairly accurately that there were at least one thousand animals in the herd. Subsequently we learned that there were many more than that; for several hundred were below our sight in the bottom of a shallow ravine.19

Of the grassland antelope, Andrews reports:

The greatest herd of antelope that I have ever seen. Thousands upon thousands of bucks, does and fawns poured in a yellow flood over the rim and spread out like a vast fan upon the plain. Perhaps fifty thousand were in the bottom of an enormous valley.20

We saw across the river, on the horizon, a small yellow streak which seemed to be moving towards us. It looked exactly like a huge caterpillar creeping on the ground. We watched it intently. The yellow streak, little by little, grew in length and width until suddenly, in a second, it spread into a large spot, which, widening and widening on either side, still kept moving in our direction. It reminded me then of a swarm of locusts, such as one sees in South America, spreading over the fields after dropping to earth in a cloud from the sky.

In a few minutes the yellow patch had grown to such a size that we realized, far as we were from it, that it covered many acres. After that we began to see in the mass of yellow hundreds and thousands of tiny dots which moved individually. Then we knew what it was. It was a great herd of reindeer, the Barren Land Caribou, migrating south.

Spellbound, we remained beside our camp fire, watching probably the most stupendous sight of wild game in North America since the bygone days of the buffalo..

That column widened like a fan until it lost itself on either side of a swarm of caribou, so closely packed together that acres and acres of gray moss were completely hidden by their moving bodies. And the noise of their hoofs and the breathing of their lungs sounded like far-away thunder. I started counting and reached three thousand. Then I gave it up. There were too many. And for what seemed to us an eternity we were surrounded by a sea of caribou galloping madly inland.21

...

While North America was better provided with bird life than with quadrupeds it is hard to exaggerate the size of the herds of bison and antelope found on the western prairies within the memory of living men. The passenger pigeons moved in such flocks that they almost darkened the sun and broke the branches of the trees on which they settled. So rare a bird as the whistling swan has been seen in flocks estimated at a thousand since 1910. Some 60,000 black brant passed Prince Edward Island in the migration of 1909. Crows gather by thousands at their roosting places in winter.

It is evident that many of these associations are not accidental; others are. The killer whale hunts in small groups. Two coyotes frequently combine to chase the jack rabbit; pelicans have coöperated to drive a school of fish ahead of them. It is likewise clear that the habits of some birds in posting sentries while the main flock feeds or sleeps contributes to the safety of all and that there is often safety in numbers. It is easy to get illustrations of the care of the young not only by actual parents but frequently by older animals in no wise related to the adopted infants. That the parents will attack possible enemies as the kingbird does the crow even in the absence of young is equally true. It is common for the male to fight for the female, but it is more rare for him to lighten her duties by setting on the eggs. Somehow we do not like to find instances where the parents eat, destroy, or neglect their offspring in order to care for foster infants imposed upon them, yet, such there are. Many fish eat the young of their own species as the pig will do at times. Insects of the same brood frequently devour each other. The cuckoo bees which have no workers frequently take possession of the bumblebees' nest, killing their queen if necessary, and then proceed to permit the bumblebees to raise cuckoo bees only.

Insect Associations

The wonderful organization of the nests of ants has caught the attention of many students and has been described so often that only passing reference is here needed. Wasmann estimates that some two thousand species of animals are associated with the ants, some as guests, some as slaves, some as parasites. We have no idea why the ants tolerate the presence of most of them. We find the ants keeping the aphids from whom they appear to get a drop of liquid of which they are fond.

Certain native ants even keep the eggs of plant lice within their nests during the winter. The sanguinary robber ant occupies herself almost exclusively with hunting and leaves the cultivation of plant lice to her slaves, these slaves being ants of a different species. The Amazon ant exists only by the capture of slaves and in that connection develops the most brilliant warrior talent that we know in the entire animal kingdom. Its mandibles are modified to be solely weapons for killing and are unsuited for domestic occupations; furthermore it has even lost the instinct for feeding by itself and must be fed out of the mouths of its slaves.22

In some of these cases the "coöperation" appears to be primarily for the advantage of the stronger party.