Agricultural zoology

The Gall Weevils (Ceutorhynchus) are very small beetles with thick-set bodies. In a state of rest the proboscis is folded back into a ventral furrow, situated between the fore-hips. They are black, and thickly covered with grey hairs. Live on cruciferous plants. The Turnip Gall Weevil (Ceutorhynchus sulcicollis), one-eighth of an inch long, dull black, with many grey hairs on the ventral side and few on the dorsal side. The deeply pitted neck-shield has in its centre a well-marked longitudinal furrow. Wing-covers deeply furrowed. The beetle appears in April, and gnaws the flowers and shoots, but can scarcely be considered as harmful. In late summer or autumn, after the sprouting of the winter rape, the female bites into the root immediately under the surface of the soil, or into the lower parts of the stem, so as to form a hole in which she lays one or two eggs. As the larva begins to develop, the surrounding parts of the stem or root grow into a gall-like swelling (Fig. 80). At the beginning of spring the developed larvæ creep out, and become pupæ in the soil; in April the beetle appears. If the Ceutorhynchus galls are only present in small numbers they damage the rape plants only to a small extent, but when ten to twelve are found in one plant the roots grow crooked, and remain short, and consequently the growth of the overground parts is detrimentally affected. Ceutorhynchus galls are found, not only on rape, but also on the different kinds of cabbage, and on turnip plants. In the last case they often occur in such numbers that the turnips do not develop at all, and the overground parts also remain small. There is a similar form (C. assimilis), as large as the preceding species, but somewhat slimmer, and, on account of greater hairiness, greyer. Appears in spring on flowering rape and several kinds of cabbage, as well as on similar cruciferous plants. It is harmful because the beetles gnaw the buds and flowers, and the larvæ feed on the seeds within the pods. The attacked pods ripen early, and open so that the larvæ fall to the ground, where they become pupæ. Usually only a single larva is found in each pod. The Rape Gall Weevil (C. napi), somewhat larger than the two preceding species, has a neck-shield which projects strongly forward like a collar, and is marked by a median longitudinal furrow. It is covered with yellowish-grey hairs. At the time when rape blooms it appears upon the flowers. The female lays her eggs singly in a hole previously bored in the stalk by her proboscis; during spring and early summer the larva eats out the stem, which turns brown inside, and becomes diseased or even dies.

Family: Chrysomelidæ (Leaf Beetles).

Small, generally thick-set beetles, arched on the upper side, with eleven-jointed antennæ thickening somewhat towards their tips, and four-jointed feet. The first joints of the feet are covered with felt-like hairs on their under sides (Fig. 81). The larvæ have three pairs of thoracic feet, and, in addition to this, there are in most species a pair of caudal pro-legs. Live in the inside parts of plants (stems, leaves), and are usually elongated and yellowish white; those which live on the outside of plants are more convex, shorter, and thicker, more or less hairy, often of a striking colour, and always with dark spots. The beetles eat leaves; the larvæ feed upon parts of the same plants, sometimes living outside upon the leaves, or it may be excavating channels in the inside of a leaf or of the stem. Most leaf beetles lay many eggs, and in many species there are several generations annually. The plants attacked by them are often stripped quite bare. Here belongs the blue Alder Leaf Beetle (Galeruca alni), the Poplar Beetles (Chrysomeli populi and C. tremulæ), the Asparagus Beetles (Crioceris merdigera and C. duodecimpunctata), etc. Of species injurious agriculturally, I will first mention the Colorado or Potato Beetle (Chrysomela decemlineata). This beetle originally lived in the west of the United States on wild solanaceous plants; but as soon as potato culture extended to the west the beetles also attacked potato plants. As soon as the insects had spread to this plant they began to appear in great numbers owing to their very great powers of reproduction; and they quickly spread from one field to another, always going further and further east. 1859 was the first year when they became notorious as pests, and, since they first appeared as such in the State of Colorado, the insect received the name “Colorado Beetle.” In a short time the beetles spread to the east, especially to places where potato culture was carried on; in 1865 they crossed the Mississippi, and in 1870 they were already spread over the states of Indiana, Ohio, Pennsylvania, Massachusetts, and New York. They were soon found in all the eastern states, and European farmers began to be alarmed. In most of the countries of Europe police regulations were made for the purpose of preventing the introduction of the unbidden guests. Colorado beetles have indeed been brought several times to Germany on board ship, but in almost all cases the pests so introduced have been recognized and caught. Twice during 1877 they were able to increase (Mulheim, Schildau), and the same thing has happened once at a more recent date (Torgau); but the vigorous action of the authorities quickly exterminated the beetles.

Beetle (Fig. 81), half an inch long, dusky yellow, with five longitudinal black streaks on each wing-cover, and black markings on the neck-shield. Larva (Fig. 82), half an inch long, thick, fleshy; legs short and weak. Orange-yellow, with shining black head, and with black spots on the body segments. The younger larvæ are darker, almost blood red. When the young potato plants come up, the beetles which have survived the winter creep out of the soil and devour the margins of the young leaves. The female lays her yellow eggs (700 to 1200?) in heaps on the leaves (Fig. 82, a). After a week the larvæ appear, and carry on the work of the beetles. They attain their full development in seventeen to twenty days, become pupæ in the soil, and the beetles of the second generation make their appearance in the middle of June. Still a third generation may appear the same year. Since a considerable time elapses between the laying of the first and second batches of eggs, one usually sees eggs, larvæ, pupæ, and beetles at the same time. Entire potato fields are eaten bare by the beetles and their larvæ, the formation of the potatoes being quite prevented. Remedies: Energetic measures must be taken on the first appearance of the beetle in any district. Where possible, all the beetles and larvæ must be collected, the plants being dug up and destroyed with the beetles, pupæ, larvæ, and eggs adhering to them. Petroleum must then be poured over the whole field and set on fire, so as to destroy any insects which may be hidden in the soil. Spraying the attacked plants with Schweinfurt green.

The Cloudy Tortoise Beetle (Cassida nebulosa)—Fig. 83. One-fifth to one-fourth of an inch long; the broad neck-shield projects in front over the small head. The wing-covers, too, are much broader than the body of the animal; they are longitudinally ribbed. Dorsal side reddish brown, in young individuals greenish; always with black spots. Ventral side black. Larva elongated oval, yellowish green. Segments of the body beset with thorn-like structures bearing lateral branches; the last segment possesses a “tail-fork,” which the larva usually carries bent over its back and on which it heaps up its dung. The beetles which have survived the winter usually attack in spring only wild goose-foot and orach plants, on which they lay their eggs in heaps. The larvæ quickly appear, and to begin with chiefly keep to the under sides of the leaves. They are sluggish, grow quickly, and devour the leaf substance; when fully developed they cement themselves to a leaf and become pupæ. In June the beetles of the second generation appear, which again lay their eggs on the leaves. In favourable weather there may be even a third generation. In many it happens that the beetles of the second generation migrate to beet or mangold plants, sometimes damaging them to a very great extent. Remedy: Rooting out species of goose-foot or orach.

The Earth Fleas, or Flea Beetles, are all small leaf beetles with the power of springing, and therefore provided with thick thighs. Here belong:—

The Rape Flea Beetle (Psylliodes chrysocephalus)—Fig. 84. Egg-shaped. Hind feet not inserted at the ends of the shanks, but higher up. The first joint of the foot is as long as the others put together. The rest of the hind foot is bent in a knee-like way on the first long joint. Shining blackish brown or blackish green, rarely brownish. Larva one-fifth to one-fourth of an inch, dusky white; head, neck-shield, and last segment of the body blackish brown. In spring and during the entire summer the beetles are found upon the plants of winter rape. Although they gnaw the leaves and the immature shoot the damage caused is small. In late summer or autumn the female beetles lay their eggs separately at the bases of the leaf-stalks of the young winter rape plants. The larvæ which emerge bore into the leaf-stalk, and eat it completely out during autumn, winter, and spring, so that the leaf dies. Since the eggs are laid separately the larvæ do not all develop at the same time in the spring. In spring many larvæ eat their way from the leaf-stalks into the still very short stem, which consequently ceases to develop. It often happens that most, or even all, of the plants in a rape field are withered; on poor soil the whole crop must be at once ploughed up; but on fertile soil the plants often develop much better than one would believe. Plants whose stem has been killed in the winter while still short may develop a few (3 to 5) branches from buds situated near its base, but these usually remain small, and do not yield a large crop. The beetles, appearing in spring, lay their eggs on the lower leaf-stalks of the rape, either on the old plants of winter rape or young plants of summer rape. In the latter case the summer rape is quite spoilt in the same way as the winter rape during the previous winter. In the former case the larvæ eat out the lower part of the leaf-stalks, and make their way into the stem, hollowing it out at a definite spot in such a way that it is no longer able to hold itself up, especially when the shoots and seeds develop. The stems bend and become kneed, sometimes to such an extent that the rape field looks as if persons or cattle had been running about in it in all directions, and treading everything down. Meanwhile the larvæ bore their way out of the stem, and become pupæ in the soil. In late summer the beetles appear, and once more lay their eggs on the leaf-stalks of the winter rape. There are, therefore, two generations annually. Remedies: Never sow summer rape after winter rape which has been destroyed by the beetle and ploughed up. Temporary limitation of rape culture.

The Cabbage Flea Beetle (Haltica oleracea), one-fifth to one-sixth of an inch long, longish oval, dark green, metallic sheen. The hind legs do not possess the peculiar features of the rape flea beetle (p. 114). Larva one-fifth to one-fourth of an inch long, greyish black, with bristly hairs, and with two rows of shining black warts. The beetles attack, in the spring, chiefly cabbage, rape, radishes, horseradish; but do not spare other plants (e.g. peas and beets) as well. Seedlings are chiefly attacked, and in all cases only young plants are devoured. Since both seed-leaves and terminal buds are eaten, much damage is done, especially during continuously dry weather. It must often happen that the beetles wander away, to find other species of plants for the purpose of egg-laying; so that it is exceptional to find the larvæ upon species of cabbage. These larvæ are much less injurious than the beetles, since they usually only prey upon mature plants. In their youngest condition they are found in groups, feeding upon the leaves; this results from the eggs being laid in little heaps. Later on, they wander away from one another. In favourable weather they are fully grown in six weeks, and several generations may succeed one another in the same year. Remedies: Destruction of the weeds which attract the beetles (charlock, shepherd’s purse, yellow rocket, treacle mustard, etc.) Good preparation of the soil, suitable manuring and drill culture, since these bring about a more rapid growth of the plants. Thick sowing (but not too thick), so that, even after the destruction of many seedlings, a sufficient number may remain. Moistening the fields by means of water-carts or sprayers. In garden-beds twigs are laid down, by which the seeds are protected against birds and the seedlings against flea beetles. “Flea-beetle machines,” consisting of a board smeared with tar, which is drawn across the field, so that the frightened beetles spring up, and remain hanging in the sticky substance. After rain, or when dew is still clinging to the plants, they should be strewed with powdered fowls’ dung, pigeons’ dung, or horse dung, wood-ashes, road-dust, powdered lime, coal-ashes; or the plan of sprinkling with a decoction of wormwood may be adopted.

The Turnip Flea Beetle, or Turnip Fly (Haltica nemorum), one-tenth to one-eighth of an inch long, egg-shaped, black, with longitudinal streaks of a sulphur yellow colour on the thickly pitted wing-covers. Larva one-fifth of an inch long, yellowish white, with dark brown head, neck-shield, and last body segment. The adult beetles have the same habits as in the preceding species; they also do damage in the same way, and attack the same plants, especially in the seedling condition. The female, however, does not lay her eggs in heaps, but separately on the leaves, and always on the under side. The larva bores into the leaf, and digs a passage, which, like the animal inhabiting it, is at first small, but gets gradually larger. In fine weather the larva is fully developed in a week. It then pierces the skin covering the under side of the leaf, falls to the ground, and becomes a pupa. Several generations may appear every year, if the weather is favourable (dry). This species is quite as harmful as the preceding, chiefly in the mature condition. Remedies: Compare the preceding species.

Family: Coccinellidæ (Lady-birds).

Hemispherical; upper side convex; under side flattened. Head small, retractile. Antennæ, eleven-jointed, thickened at their tips. Legs short; feet apparently three-jointed—in reality four-jointed, the second joint, however, being very small. Colour, usually variegated; many species black with red, or red with black spots. When grasped, they let a yellowish, unpleasant-smelling fluid escape from the abdomen. The blunt, four-cornered, usually variegated pupæ hang on the leaves. The fully developed larvæ are longer than the beetles. They closely resemble those of the leaf beetles, but are not so thick-set, and their longer legs stick out more laterally. They are covered with warts and little spines (Fig. 85). The larvæ and beetles of most species feed chiefly on aphides and shield-lice; they are therefore of use, and this is especially true of the exceedingly ravenous larvæ. The larvæ of the Seven-spotted and Two-spotted Lady-birds, in particular (Coccinella septempunctata and C. bipunctata), are found in large numbers among aphis colonies. The yellow eggs are laid in heaps.

Second Order: Orthoptera (Straight-winged Insects).

Insects with biting mouth-parts and incomplete metamorphosis (p. 89). Four wings, of which the anterior are usually harder than the posterior; hind wings membranous, broader than the fore wings, and folded like a fan. The Orthoptera feed entirely, or almost so, upon vegetable substances. To this order belong:—the Earwigs (Forficulariæ), which feed on sweet fruits and flowers, and are sometimes very injurious; the Cockroaches (Blattariæ), which do much damage to provisions in kitchens, stores, and on board ship; the Grasshoppers (Acrydites), to which, besides the Migratory Grasshopper (Acrydium migratorium) Fig. 62, various species of meadow grasshoppers belong, which are quite harmless; the Locusts (Locustidæ), to which the well-known Green Locust (Locusta viridissima) belongs; and the Crickets (Gryllidæ), to which belong, among others, the House Cricket (Gryllus domesticus), the quite harmless Field Cricket (Gryllus campestris), and the Mole Cricket (Gryllotalpa vulgaris).

1⅗ to 2⅗ inches long; spread of the wing, on the average, 2½ inches. Greenish grey. Under side flesh colour. Wing-covers brownish, darkly flecked. Colour very variable (Fig. 62). Excessive multiplication and migrations of this insect often take place in South Russia and Turkey; but they may also appear in Central Europe. In North Germany, for example, the following years of this century were “grasshopper years:” 1803, 1825–27, 1853, 1875–76. In many cases the appearance of swarms of grasshoppers in Central Europe is due to migration from Russia and Hungary; but it also often happens that the insects which appear in such large numbers have been bred in the places where they are found. Since the female lays, on the average, 150 eggs, excessive increase may take place in any country to which they are indigenous—and therefore in Central Europe. It appears, however, that a large number of grasshoppers are usually killed by their natural enemies, such as cold and damp weather. Excessive increase may, however, take place in exceptionally favourable years; and since the larvæ, which are incapable of flight, devour everything available, the mature insects developed from them are forced to migrate. Where they descend they destroy everything they find in the fields. Remedies: Destruction of the longish eggs, which are laid in heaps in the earth of fallow ground and meadows. In all those places where dead insects are found in large numbers on the ground many eggs will also be discovered, for the insects keep on laying till they sink down dead in the place where the last heap of eggs was deposited. Such places should be dug or ploughed, and the eggs, which are present in thousands, either collected or else searched out by pigs, ducks, geese, and fowls, which have been driven to the spot. Destruction of the young animals while still incapable of flight. Working the soil with harrows, rollers, and cultivators will be effective here. The adult grasshoppers must for the most part be destroyed with fire. [Heaps of straw and brushwood are soaked with paraffin and then set on fire.]

The Mole Cricket (Gryllotalpa vulgaris).

Body stout and flattened. Antennæ, palps, and tail-filaments very long. Fore legs broad, modified into true “digging legs,” superficially resembling the feet of a mole. Fore wings broad, but short, leathery. In a state of rest, the hind wings lie on the back, like a couple of tails. Colour dark brown. Principally occurs on peaty soils mixed with sand or clay, also on all soils which have become of firm consistency by the application of much manure. Their presence is therefore local. Very early in the year the mole-cricket leaves its winter hiding-place, and begins to make its passages near the surface. Where the female makes her nest the passage turns downward a little. The nest is 1⅗ of an inch in diameter, and its walls are compacted by the pressure of the hard body. The number of eggs is from 200 to 250; they are laid in lots with a few intermediate spaces. The young creep out in the spring, and are wingless. To begin with, they are white, but quickly become brown. The mother guards her young very carefully. These grow tolerably fast, and first begin to lead an independent life after the second moult. In October and November they undergo a third moult. Then, still in a wingless condition, they hide themselves, and do not moult again till April or May, when the wing-cases appear; while after the fifth moult (May, June) the mole-cricket becomes an adult insect, capable of reproducing. This insect is found in cornfields, gardens, grassland, and meadows, also in orchards and woods. It gnaws the roots of all kinds of plants, and often effects great damage in this way. The mole-cricket is also harmful on account of its passages, which are dug close to the surface. In this way it lifts young plants out of the soil; while older plants are killed, both by its gnawing and by its digging. Such plants can often be pulled up by grasping the leaves. All the plants wither in the place where the nest is found. Dry, cold winters kill almost all the mole-crickets; much drought in summer and also continuous wet are unfavourable to them. Enemies: moles, rooks, etc., butcher-birds, starlings, and the larger ground beetles. Remedies: Destruction of the nests, in June, to begin with, but also to be continued later. In those parts of a field where the plants are yellow or withered in a large circular patch (some 39 inches in diameter) the nest is felt for with the finger, and carefully lifted up, so that the eggs do not fall out. Mole-crickets can also be caught by means of flower-pots. The apertures in the bottoms of these are stopped with corks, and they are then sunk in the soil with their mouths on a level with the mole-cricket passages; they thus serve as pitfalls, from which the insects cannot escape. If during winter little heaps of horse dung are placed on the ground, the insects creep into them for the sake of the warmth, and can thus be collected and killed.

Third Order: Neuroptera (Net-winged Insects).

Insects with biting mouth-parts and four similar membranous wings, with numerous veins arranged in a net-like manner. The metamorphosis is either incomplete (p. 89: dragon flies, may flies, book lice), or complete (p. 89: ant lions, lace flies, snake flies, scorpion flies, caddis flies). The indigenous forms, with the single exception of book lice, feed upon animal food, usually on the juices of other insects. Several of them are tolerably useful in this way.

The Dragon Flies (Libellulidæ) fly about incessantly from place to place on bright warm days, and catch a large number of insects, especially butterflies and flies, among which are many that are harmful. The larvæ live in water, and feed on insects and such small deer, which, however, are of no importance to forestry or agriculture. They also devour fish-spawn, and may therefore be injurious in that way.

The Lace Flies (Hemerobidæ) when at rest are covered as with a roof by their fore and hind wings, which are almost alike, clear as glass, and finely veined. Head tolerably large, eyes large, abdomen elongated and slender. The extremely rapacious larvæ (Fig. 86, b) feed on the juices of the bodies of other insects, which they suck up by means of a pincer-like organ situated on either side of the mouth. The two pincers are perforated, and the tubes open on each side into the gullet; the body juices of the insects attacked thus flow into the gut of the larva. This is strongly built, and always much thicker and larger than the adult insect. Metamorphosis complete. Three genera belong to the lace flies:—

1. The delicate greenish, or greenish yellow, illsmelling Gold-eyed Lace Flies (Chrysopa), the larvæ of which chiefly feed on plant lice (a few species on caterpillars, also, and other small insect larvæ).

2. The Aphis Lions (Hemerobius: H. hirtus, with hairy veins on the fore wings; H. dipterus, with hind wings almost entirely absent), the larvæ of which also feed on aphides, and make a case from their sucked-out skins.

3. The Ant Lions (Myrmeleon), of which the fat, thick-set larvæ, which have a large head and strong grasping pincers, dig out in the sand funnel-shaped holes, at the bottom of which they hide, lying in wait for ants and the like, which step on the edge, when the sand gives way and causes them to fall in. The species of the first two genera are of service as destroyers of aphides; the ant lions are of no importance.

The Scorpion Flies (Panorpatæ) have attached to the head a kind of proboscis, the upper side of which is formed by a prolongation of the forehead, and the under side by the maxillæ and lower lip, while the upper lip and mandibles are hinged on at its tip. Here belongs the slender-bodied Scorpion Fly (Panorpa communis), an insect found in May, and again in July or August, on the leaves of trees and shrubs, when it is sunny. While the abdomen of the female ends in an ovipositor, it bends upwards in the male, and terminates in a pincer-like organ; hence the name “scorpion fly.” Wings flecked with brown. Scorpion flies catch on the wing a very large number of butterflies and moths, and are therefore useful to some extent.

Fourth Order: Hymenoptera (Membranous-winged Insects).

Upper lip and mandibles short; the latter used for biting. Maxillæ loose-jointed, so that they can be stretched out considerably; elongated in those which lick the juices of flowers. In the last-named forms the larva’s lips are still more elongated, and may even form a tongue or proboscis-like organ, which may bear lateral appendages (“secondary tongues”). Wings, four, all membranous, with relatively few veins (Figs. 61, 90). Metamorphosis complete; larvæ very various; pupæ free (p. 93). The female usually possesses an ovipositor, the structure of which varies a great deal, and which serves in many species, not only for egg-laying, but also for protection (digging wasps); in others exclusively for offence or defence (“stings” of bees and wasps), while the same opening serves for the passage both of eggs and excrement. The abdominal glands, secreting a sticky substance by which the eggs are attached, are modified into poison-glands in those Hymenoptera which possess a sting. In those forms where the ovipositor is not modified into a sting, it is used for piercing, biting, or sawing. The Hymenoptera with saw-like ovipositor first make an opening in wood or in a leaf by means of the saw-teeth in its edge, and then lay an egg in this hole.

Many Hymenoptera (all digging wasps, gold wasps, ichneumon flies, and gall flies—several true bees and wasps) live alone, or in pairs. Others form colonies, in which division of labour is always so far carried out that there are reproductive individuals and workers. The former (males and females; in colonies of bees—“drones” and “queen”) are only present in small numbers in any particular colony. They live merely for the perpetuation of the species. At most the males seek their own food, while the females are usually fed by the workers. Workers, on the other hand, are individuals in which the (female) reproductive organs remain in a low state of development, so that they are sterile. They seek food for the larvæ, and usually for the adult reproductive individuals as well. They also wage war against strange intruders.

Family: Apidæ (Bees).

The bees, by means of their very much elongated mouth-parts (maxillæ and lower lip or “tongue”), collect honey from many different kinds of flowers. Body somewhat unwieldy, usually hairy. The fore wings are not, as in wasps, folded together longitudinally when in a state of rest. Eyes round. The legless, almost maggot-like larvæ are fed with pollen or with a mixture of pollen and honey.

Most bees are colonial, and in these we find, besides the reproductive individuals, workers which prepare the nest. This is for the most part made up of “cells,” in the construction of which the most various substances are used according to the species, e.g. wax, sand grains, chewed wood, fragments of leaf. In each nest there is at the same time only one queen, who lays her eggs in the cells; the larvæ are therefore developed in these cells, other cells serve for the storage of pollen or honey. In the non-colonial bees there are no workers; in a few of these species (parasitic bees, cuckoo bees) the female lays her eggs in the cells of other species, which, like foster parents, undertake the care of the strange larvæ. These species are naturally devoid of the apparatus for securing and carrying pollen. In several bees (honey bees, humblebees) this end is attained by the much-broadened shanks and first, very large foot-joints of the hind legs. Other bees (Megachile) carry pollen on the under side of the abdomen.

Bees play a very important part in the pollination (fertilization) of many cultivated plants.

The Honey Bee (Apis mellifica) cannot be spoken of here; reference must be made to works on apiculture.

The Humblebees (Bombus) are tolerably large, stout, thick-set, and hairy. They construct nests below the surface of the soil (often in peaty places), made up of oval or irregular waxen cells the size of a hazel-nut. They fly rapidly, always making a humming sound. Many species are black, with yellow and white, or red transverse stripes.

Honey-producing flowers in which the corolla is so long that even the proboscis of humblebees cannot reach the honey hidden at the bottom of the flower, (tobacco, field and garden beans) are gnawed at their base by the sharp mandibles of the bees, so that a hole is made in the calyx and corolla through which the tongue can be put. In this way the ovary is sometimes wounded, and the normal development of the fruit rendered impossible. Perhaps a certain amount of damage, always however inconsiderable, may thus be effected.

Family: Vespidæ (Wasps).

Mouth-parts as in bees. Also with stings. Slender, and either hairless or only slightly hairy. Eyes kidney shaped. Fore wings folded together longitudinally when at rest (Figs. 61 and 88).

A distinction is made between solitary and social wasps; the latter possess males, females, and workers. Only the fertilized queens survive the winter. In the spring each of these begins to construct a nest (Fig. 88). In the wasp’s nest each comb consists only of a single layer of cells, the openings of which are turned downwards. In a single nest several of these horizontally placed combs are usually found one over another, and are connected together by means of vertical pillars. Some nests are built in hollow trees, others in holes in the ground; others hang freely from trees, in which case they are covered by several layers of a papery substance. The combs and cells are also made of paper, to prepare which the insect gnaws and crushes decaying wood, and especially bark, with its mandibles, mixing the crushed material with saliva. In this way a pulp is made which is used in the construction of the nest, and dries into a kind of paper. The opening of the nest is in its under side (Fig. 88).

During spring and summer the queen, or “wasp-mother,” lays only eggs from which workers are hatched, which undertake the work of nest-construction and care of larvæ, so that the queen can devote herself exclusively to the function of reproduction. Towards autumn males, and females capable of being fertilized, are also hatched; these last afterwards live over the winter in the fertilized condition.

During summer the larvæ are fed by the workers with finely chewed insects or with honey. They do not, however, suck the honey from flowers, but steal it from several species of bee, or else form it in their stomachs from sugary materials drawn from sweet fruits.

Wasps are harmful or troublesome in three ways: (1) by gnawing the bark of trees; (2) by feeding on sweet fruits; (3) by the painful stings which they inflict. These are most dangerous in hot summer days. If a nest situated in the soil is destroyed during ploughing the alarmed insects attack both men and horses, cases being known where their stings have proved fatal. The pain is chiefly caused by the poison introduced into the wound. On this account if the sting remains sticking in the skin it must not be drawn out simply with the fingers, but carefully, by means of the nails, lest the poison-bag is pressed and thus still more poison brought into the wound. Remedies: Cooling substances, e.g. ground carrots, apples or pears, cabbage leaves, damp sand. Rubbing in ammonia. If there is acute inflammation, a compress with sugar of lead.

Family: Fossores (Digging Wasps).

Several species of this group resemble the wasps in their habits, as well as through their black and yellow-tinged abdomens; but they are always distinguished from these by their fore wings, which are not folded together in a state of rest, and by their eyes, which are not kidney shaped. The shanks and feet possess thorns serviceable for digging. The sting of the female has no barbs, so that it is not torn off and left behind in the wound. The digging wasps are not social. They are lively and active; in summer the female often flies busily about near the ground in order to find a place for bringing up her young. She digs a hole in the earth in which she lays an egg. Then she buries an insect to serve as food for the young when hatched. Lest the insect to be buried should decompose, while, on the other hand, a living animal would not allow itself to be buried, the wasp first brings the insect into a condition in which it cannot make any voluntary movements. For this purpose most species sting the captured prey several times in the body, and thus often injure the ventral ganglia (p. 84); by this treatment the insect is not killed, but reduced to a condition of apparent death. Most digging wasps are useful, since they chiefly bury destructive kinds of insects. The Common Sand Wasp (Ammophila sabulosa, Fig. 89), buries caterpillars; the Path Wasp (Pompilius viaticus), spiders; the Weevil-killing Sand Wasp (Cerceris arenaria) and the Fly-killing Sand Wasp (Mellinus arvensis) respectively bury weevils and flies.

Family: Formicidæ (Ants).

Large strong mandibles adapted for biting; maxillæ and lower lip not prolonged like a proboscis. Workers wingless; the males and reproductive females have weakly veined wings. In correspondence with these facts, the mesothorax which bears the larger wings is most strongly developed in the last, but the prothorax in the workers. Abdomen united with the thorax by a one- (Formica) or two-jointed (Myrmica) stalk. All female ants, and naturally workers too, possess poison-glands, the secretion of which accumulates in a poison-bladder; but the sting is lacking in all species of Formica. The stingless ants (e.g. the Red Wood Ant, F. rufa) inflict a wound with their strong mandibles, and then, bending the abdomen forwards under the thorax, squirt the contents of the poison-bladder into the wound. Ants form colonies, always of large size, and consisting of reproductive and sterile individuals. Their food is both of animal and vegetable nature, but chiefly consists of insects and similar small animals. They mostly devour caterpillars, but also dead or wounded beetles (e.g. cockchafers), mammals, birds, and reptiles. As destroyers of caterpillars they are of use, but this is true more of those living in woods than those which inhabit fields and meadows. Ants are fond of all sweet substances; when they enter houses the sugar jar is very often the end they have in view. They are particularly fond of licking up the sweet juice which aphides excrete from their abdomens. On plants infested with aphides many ants are found which greedily sip up all the drops hanging from the abdomens of the aphides; they may even promote the shedding of the juice by stroking the abdomens of the little animals with their antennæ. There are, indeed, species of ants which carry the aphides to the plant parts on which they thrive best, and again, when these are sucked dry, transport them to other uninjured parts. Sometimes aphides are kept in the overground or underground nests of the ants. The common yellow meadow ants shelter aphides in their subterranean nests, where they live on the roots of grasses and other plants. In order to get, when necessary, fresh food for these “milch kine,” they occasionally enlarge the nest, so that new plant roots are laid bare, and they then carry the aphides to these.

During the greater part of the year only workers, larvæ, and pupæ are found in an ants’ nest, but reproductive individuals appear in summer, disappearing again before the cold weather comes on. As soon as there is a sunshiny day they fly out, usually in large numbers. After pairing, the females let themselves fall to the ground; they then either tear off their own wings or this is done for them by the workers, which search them out and take them to the nest, where the laying of eggs quickly begins. The legless larvæ have feebly developed mouth-parts, and are fed by the workers on food broken down by them. The pupæ vary; in the sting-bearing ants (Myrmica) they are naked, in the stingless ants (Formica), on the other hand, they are invested in a cocoon. The latter kind of pupæ, known by the incorrect name of “ants’ eggs,” are collected and used as food for insect-eating birds. The nests are made either out of pine-needles and small branches heaped together (Red Wood Ant = Formica rufa), or they eat out passages and cell-like spaces in sound tree trunks (the larger Wood Ants, e.g. F. herculeana and F. ligniperda) or in decayed tree trunks (Small Wood Ant = F. fuliginosa); others (Yellow Wood Ants = F. flava, etc.) make passages and cavities in the ground, throwing up the earth into ant-hills. Damage: Several species do harm by excavating the soil, either in meadows and cornfields, by which the plants are killed and harvesting rendered difficult, or under summer-houses and dwelling-rooms. Others destroy tree stems. They are indirectly harmful on account of the way in which they care for aphides, causing these pests to increase to a greater extent than would otherwise be the case. Remedies: If ants have got into a room the nest must be found if possible, and the insects there destroyed with paraffin or boiling water. If it proves to be too difficult to find and destroy the nest, all the openings by which the ants can enter must be stopped up with lime to which some extract of colocynth has been added. The nests found in fields and gardens may sometimes be destroyed by quickly digging them up, pouring paraffin over them, and then igniting it. It is also a good plan to frequently tread or roll down the ant-hills which are thrown up, as in this way they will be dispersed in the end. Ants are of service in forestry, but scarcely in agriculture.

Family: Ichneumonidæ (Ichneumon Flies).

The species of ichneumon flies deviate in many ways from one another, but they all have similar habits and play a similar part in nature. They all have a longer or shorter ovipositor, always surrounded by two flaps, and serving for laying eggs in other animals. Those which seek their prey in branches and leaves generally possess a very short ovipositor not obvious on cursory examination; those which lay their eggs in insects inhabiting crevices, e.g. wood insects, are often provided with a very long ovipositor. No colonies and, consequently, no workers.

The female ichneumon fly generally lays her eggs in the body of an insect larva, on which the ichneumon larvæ developed from these eggs feed, using up the reserve matter stored up in the fat body (p. 92). Caterpillars are most infested; then follow false caterpillars, and then the larvæ of weevils and leaf beetles. The eggs of a few kinds are laid in pupæ, or even in the eggs of moths and butterflies. They always select for this purpose those insects which possess reserve material. The large kinds of ichneumon fly lay only a single egg in one host, especially if the latter is not of large size; many of the smaller ichneumons, on the other hand, lay many eggs (Fig. 90) in one host, even up to a hundred or more. A caterpillar containing ichneumon eggs does not at first appear different from other caterpillars, except that a dark spot or patch usually indicates where its body was pierced by the ovipositor of the ichneumon fly. The parasite breathes while in the host by bringing the tip of its abdomen (where the main stem of the air-tube system opens) into connection with one of the host’s spiracles. Since the larva feeds altogether upon perfectly digestible substances an anus is superfluous and is absent. Many ichneumon larvæ are ready to become pupæ when the host is about to pass into the same condition; the larva then bores through the skin of the latter, which quickly dies. Other species do not attack the organs of the host so soon, but allow it to become a pupa in peace, and then themselves become pupæ inside it; later on, one or several ichneumon flies come out of this pupa instead of a moth or butterfly. It is obvious that ichneumon flies are very serviceable by destroying a large number of harmful insects. They cannot, indeed, prevent the increase of any particular noxious insect, but, when this takes place, they themselves increase to a greater extent, and finally appear in such numbers as to make an end of the pest.