Popular Science Monthly/Volume 5/May 1874/Observations of a Naturalist in Nicaragua
MR. CHARLES BELT has given us, in an interesting volume, the results of his natural history studies during a residence of four years in Nicaragua. His opportunities were excellent, and he has the faculty of turning them to good account. He found the climate of the region of almost uninterrupted summer, with abundant rainfall excepting in localities on the western slopes of mountains, and consequently a great profusion of animal and vegetable forms of life.
The eastern belt of the country is described as one unbroken forest, where perennial moisture reigns in the soil, perennial summer in the air, and vegetation luxuriates in ceaseless activity. Unknown are the autumn tints of English woods and the unrivaled splendors of the foliage of Canada. The trees do not grow in clusters, like our firs and oaks, but crowd upon each other in unsocial rivalry, struggling to keep their upper branches and leaves in the sunlight. A vast network of cable-like plants entangles the trees, and gorgeous air-plants dangle everywhere.
The central belt is of elevated grounds and grassy savannahs, but the Pacific slope is of rich, deep soil of decomposing tufas, where tropical fruits are abundant and prolific. It is an interesting fact that the mountains show everywhere traces of former glaciers. Enormous bowlders, beds of bowlder-clay and unstratified gravels, and rocks with smoothed rounded surfaces, suggest the former presence of ice.
In the profusion of animal life the struggle for existence is intense and incessant, and Mr. Belt was at once impressed with the extent to which protective coloring and other mimetic resemblances were found to exist. Thus wasps and stinging ants have hosts of imitators among moths, beetles, and bugs. A curious longicorn beetle was found covered with long brown and black hairs, closely resembling hairy caterpillars, common in the bushes, but which birds are known not to touch. The well-known phasma, or leaf-insect, escapes danger and eludes observation by its wonderful resemblance to leaves; and one species of this insect, in its larval stage, is called the moss-insect, and so closely resembles the moss it inhabits as not to be distinguished from it unless disturbed. The same is true of spiders which assume a resemblance to the petals of flowers in which they hide.
A curious green lizard was common in the wild-canes and grass, having leaf-like expansions, on account of which it was with great difficulty detected; and a spider so closely resembled, in form and color, a black ant, that it was mistaken for that insect. It had, more-over a habit of elevating its fore-legs so as to exactly resemble antennæ. Various species of stinging ants, which no bird would touch, were mimicked by spiders which were not distasteful to birds, as Mr. Belt proved.
So universal is protective resemblance among insects, in Nicaragua, that Mr. Belt was sure that whenever he found a species provided with special means of defense, others imitating it might be found also, and such indeed was the case invariably. It was noticed that insectivorous birds and mammals did not destroy the fire-flies, which were very abundant, and several insects, especially species of cockroaches, mimicked them, and in a perfectly fearless manner made themselves conspicuous, instead of resorting to hiding-places as is the custom of their tribe.
Those insects which were protected by special means of defense exposed themselves without fear, and rather made a display of their qualities. With the brilliant Heliconii butterflies, wasps of rich metallic lustre, fire-flies, and many other species, this was very obvious. Perhaps the display of their destructive features is a warning, otherwise they might be destroyed by their natural enemies, although not eaten. Thus a brilliantly-colored frog would come forth fearlessly during the day when others were concealed, and it was at once assumed that no animal would feed upon it; and, on offering it to fowls and poultry, not one would touch it excepting a duck, which at once threw it down and shook its head with evident dislike. Mr. Belt suggests that the white tail of the skunk laid upon its back makes it conspicuous in the dark, and may be a sort of warning to animals which would do it injury.
A most interesting instance of mimetic appearance and habit was afforded by a green, leaf-like locust. This insect would remain perfectly motionless, exactly resembling a leaf, while its enemies, a species of foraging ants, would run over it, and around it, destroying every insect in their way. The locust might be taken up and dropped again among the ants, still motionless as if dead, thus escaping injury.
These wonderful features in animal life had previously been studied by Mr. Bates in his researches in the valley of the Amazon, and by Mr. Wallace in several works, and strikingly illustrate the possibility of change in the structure and habits of living creatures. If this were not the case, how surely all types of animals and plants would disappear with the change of their environment! Mr. Belt calls attention to the fact that we are not to understand that one animal's imitating another is a conscious act. Perhaps we know very little of consciousness in these lowly creatures, but it is quite certain that they are conscious of danger, experience fear, and impulse to seek safety. Nor can we doubt that in these may originate those modifications which inaugurate protective resemblances which afterward become so marked. Natural selection is the present and efficient means by which the modified forms are preserved; those most favorably modified most readily escape destruction, and thus the fittest survive amid inevitable dangers.
Perhaps all insects have natural enemies which they fear, and this instinct of self-preservation is active and acute; and it would be strange indeed if these conditions found no expression in those modifications of both form and habit which secure safety to the creature, and afford means of defense as well as of attack.
The well-known habit of animals in making their nests or burrows in places of safety was noticed in a species of birds which build their nests in bushes infested by stinging ants: a small parrot builds in a hole made in the nests of the termites, and a small fly-catcher builds alongside of the nests of one of the wasps.
The account given of the foraging ants (Ecitons) is most interesting. They live solely on insects and similar prey; ransack houses, and clear them of insects of every kind. They appear to be without fixed abodes, and advance in columns three or four yards wide, with flank, advance, and rear columns, millions in number. Their presence is announced by the noise of birds, as trogons, ant-thrushes, and others, which follow them for the insects which take wing, terrified by their destroyers. Grasshoppers, cockroaches, and others, are seized, bitten in pieces, and the fragments conveyed to the rear of the columns.
The temporary abodes of these ants seem to be a crevice or dense mass of brushwood, but in a few days they are off to new grounds. Small parties ascend trees in search of wasps' nests, and, if found, information is conveyed to the swarms below, when a column ascends, takes possession of the nest, and devours or removes the young, the wasps being powerless before the multitude.
While ants which hunt singly have eyes well developed, the eyes of the Ecitons are small, imperfect, and in some species wanting, and they evidently follow each other by scent. This was shown in the following manner: A party or column following a leader will become distracted if his track, which they will follow in its minutest windings, is interfered with. Mr. Belt scraped away the clay which the leader had gone over, and the followers were completely at fault until they had gone around the scraped portion, when, on striking the trail again, their hesitation vanished, and they followed it with the greatest confidence.
They aid each other in difficulty with a sympathy and intelligence that are extraordinary, and overcome dangers of very rare occurrence. On one being partially buried with atoms of clay, the others removed them; a small lump, too heavy for them to move, was instantly bitten to pieces, a dozen or more being summoned to assist. They aid each other in ascending steep places, in crossing water, and in every movement afford evidence of wonderful social order.
Not less interesting than these were the leaf-cutting ants (Œcodoma) common in tropical America. Their order, sagacity, and underground abodes, were a subject of wonder and study. All introduced species of trees are directly attacked by them, and, unless carefully watched, are destroyed. Mr. Belt turned the tide of war by pouring a strong solution of carbolic acid, in water, into their formicaries; straightway the hosts left his plants to attend to home-affairs, and the removal of dead ants, food, and undeveloped larvæ and pupæ from their dwellings to a new home, was carried on with extraordinary zeal. The old burrow was deserted, and their ravages for a time suppressed. Corrosive sublimate makes the ants mad and furious. A little of the powder was sprinkled in one of their paths; so soon as the ants touched it, they ran wildly about attacking others, and very soon compact masses, or balls of ants, would be found biting each other. Huge fellows from the formicaries, measuring three-quarters of an inch in length, came forth to set matters right, but on touching the poison their bravery forsook them. They attacked others, and were themselves attacked, and became the centres of balls of furious ants.
Many indigenous trees escape their ravages, evidently because distasteful. Through long ages the ants and trees of tropical America have become somewhat modified together. All plants disliked by ants have a great advantage over others, and thus a selection has gone on, in which introduced species do not share. The lime is less liked than the orange or the citron, and, while these are inevitably destroyed, unless protected, the lime would probably survive; and Mr. Belt judiciously remarks that a little more or less acridity, or a slight chemical difference in the composition of the tissues of a leaf, so small that it is inappreciable to our senses, may be sufficient to insure the preservation or the destruction of a species throughout an entire continent. The paths of these ants ramify in every direction from their abodes, and are more thronged than the streets of London. They seek the open spaces near margins of the forest, and excavate a series of galleries, which are the scene of manifold operations. Continually the workers bring in burdens consisting chiefly of fragments of leaves. Naturalists have differed as to the use to which these leaves are put. Some suppose they are used as food, others, to line their galleries; the explanation given by Mr. Belt is, that the leaves are used as a manure, on which grows a minute fungus, which is the food of the ants; that they are, in reality, mushroom growers and eaters. This extraordinary conclusion he arrived at by careful observations. He repeatedly explored their nests, which are a series of rounded chambers about as large as a man's head, connected by tunneled passages leading from one chamber to another. In the burrows the leaves could never be found in quantity; they were evidently directly used up; but the chambers were about three-fourths filled with a speckled-brown, spongy-looking mass. Throughout this were ants with pupæe and larvæ. Upon careful examination, it proved to be minutely subdivided leaves, brown and withered, overgrown and lightly connected by a minute, white fungus, that ramified in every direction through it. This fungus was found in every chamber opened, and in the midst of it ant-nurses and immature ants. When the nests were disturbed, this fungus, or ant-food, was guarded with great care, and every atom of it was removed as soon as possible, if the old abode was broken up. That the leaves were not eaten was shown by the fact that the refuse in many deserted chambers was composed entirely of their decayed fragments, exhausted as a manure for the fungus, and left as food for larvæ of several species of beetles. Some leaves were evidently unsuited to the purposes of the ants. Grass, if carried in, was directly brought out again, and thrown away. The carriers of this were probably young ants, and may have got a severe ear-wigging for their stupidity. After all, then, do ants, like hosts of other animals, learn by experience, and is instinct, so called, sometimes at fault?
Bates describes the sand-wasps, on the banks of the Amazon, which, on making a hole, carefully examine the locality before leaving it to procure food, and Mr. Belt noticed similar actions in repeated instances. They take the same precautions that a man would do, who wished to return to the same spot. Frequently, after going a few rods, they will return, fly around for an instant, and then dart away. On one occasion, a portion of a green caterpillar was carried away by a wasp, which, on returning for the other portion, missed its mark on alighting, and became quite lost, when it took wing again, made circles around the spot, and again alighted, but in vain. This was repeated half a dozen times, and the insect seemed to get angry, buzzing loudly, when finally it found its prey.
Butterflies of several kinds are described as abundant, but the migration in enormous swarms of one or more species, which occurred every year, is an interesting phenomenon.
Flights of butterflies were thus described by Darwin in 1832: "When off the shores of Northern Patagonia, we were surrounded by vast numbers of butterflies, in bands or flocks of countless myriads, extending as far as the eye could range; even with the aid of a telescope, it was not possible to see a space free from butterflies." Mr. Belt had seen immense migrating flocks in Brazil, journeying southeastward, as were all those seen by him in Nicaragua. These were a brown-tailed species (Timetes chiron), and there were no return-swarms, but a continuous migration in one direction only. The gilded, day-flying moth (Urania leilus), and a few yellow butterflies, were seen with the migrating hosts.
Birds, which are abundant at all seasons in the country, have a habit of associating, possibly for safety, or, as Mr. Belt suggests, to assist each other in hunting for food. Thus, flocks of hundreds, comprising a score of different species, are frequent, and, when present, the trees seem alive with them. He could scarcely go abroad without meeting them; fly-catchers, woodpeckers, tanagers, creepers, trogons of several species, all associating, apparently, on the most friendly terms, for mutual help.
The natives found about the country, as well as in the towns, represent an inferior type of civilization. They are, as a rule, excessively indolent and thriftless, the mixed races much more so than the native Indians. Idleness is the curse of Central America, and the people are content to live in squalid poverty rather than work. Dio Filiberto was a thrifty man, and told the traveler that he was building a new residence, and showed him outside his hut four old posts, used for tying cows to, which had evidently been in the ground many years. "There," said he, "are the corner-posts, and I shall roof it with tiles." Long, no doubt, will he lounge at evening, when his wife and children are milking the cows, and feel proud, as he views the four old posts, that he is building a new house.
The habitations of the Indians, mere shelters as they are, are generally quite cleanly; and this class of the population is invariably fond of flowers. On all important occasions, beautiful and fragrant flowers are used for decoration, a trait of the old Indians which survives with their unfortunate descendants.
Mr. Belt's descriptions of natural scenery are vivid and impressive. The night-world he describes as being very different from that of the day. Things that blink and hide from the light are all awake and astir when the sun goes down. Great spiders and scorpions prowl about, or take up advantageous positions where they expect their prey to pass. Cockroaches, of all sizes, from that of one's finger to that of one's finger-nail, stand with long, quivering antennæ, watching for their numerous foes, or scurry away from danger, as fast as their legs can carry them; but, if they come within reach of the great spider, they are pounced upon in an instant, and, with one convulsive kick, give up the struggle. Centipedes, wood-lice, and all kinds of creeping things, come out of cracks and crevices; the pools are alive with water-beetles, which have been hiding in the ooze all day. Owls and night-jars make strange, unearthly cries. The timid deer comes out of its close covert to feed on the grassy clearings. Jaguars, ocelots, and opossums, slink about in the gloom. All the day-world is at rest and asleep. The night speeds on; the dawn is saluted by the song of birds, and the creatures of night hurry to their dens and hiding-places. As a traveler, naturalist, and observer, Mr. Belt has done excellent service, and the reading world is his debtor.