Our crane-flies, or daddy-long-legs, when they swarm about the grass are intent on two objects. They do not require food; they have had enough when they were grubs concealed in the soil. They are now busy, first, in pairing, so that the females' eggs may be fertilized; and, secondly, the females are about to choose a likely piece of ground in which to bore with their pointed tails and lay their eggs. They prefer rather damp spots, shaded from the fierce drying heat of the sun, for this purpose. When laying her eggs, the female balances herself with her legs in an upright position, and, pushing the sharp tail into the earth, moves round by the aid of her legs, to the right and to the left, so as to bore a quarter of an inch or so into the loose soil. Then she lays two or three eggs, and, coming down from her upright pose, moves on through the blades of grass for 3 or 4 inches, and again takes an upright attitude, and repeats the boring and egglaying. The eggs are very small, black, shining grains, of which as many as 300 are found in the body of one ripe female. The male crane-fly has a broad, somewhat expanded end to its body, by which it is easily distinguished from the female.
From the eggs minute maggots or grubs hatch and feed upon animal and vegetable refuse in the soil, but as they increase in size they burrow an inch or so into the ground among the grass roots. There are two broods, one in spring and a more abundant one in August and September. The grubs have no legs. Insect grubs are often legless, as, for instance, the maggots or "gentles" of bluebottle-flies. Or they are provided with short legs, as, for instance, are the "caterpillars" or grubs of moths and butterflies. The grubs of the crane-fly ([Fig. 22, B]) show eleven rings or segments to the body, and have a tough grey or brownish skin, which is so firm as to give them the name of "leather-jackets." They have a head provided with a pair of short, strong mandibles or jaws, and a very short pair of feelers (antennæ). These grubs grow to be an inch and a half long, and are two-thirds the thickness of a common quill pen. They gnaw with their hard jaws the young shoots and roots of grass, and do an enormous amount of damage to grassland. They are rarely seen except when a sod is lifted, but in late spring and summer, when the grub changes to a motionless pupa or chrysalis, they may be seen protruding for about a third of their length from the surface amidst the grass tufts. Birds eat them and rooks dig with their beaks into the sod in order to pull them out, leaving a number of small pits (on the golf links) where they have been at work. The proper name of these injurious grubs is "leather-jackets." They are often confused with another grass-and-wheat pest, the "wire-worm," and are in consequence sometimes called "false wire-worms." The "wire-worm" is the grub of a beetle ([Fig. 22, C and D]), and is very different in appearance and history from the "leather-jacket," though both of them do great damage to grass and to grain crops.
The common crane-fly, or daddy-long-legs, is called Tipula oleracea by entomologists, and is abundant in Europe as well as in these islands. There are other "species" of the genus Tipula common in England, namely, a smaller kind with spotted wings, Tipula maculosa, or the spotted crane-fly, and a large kind called Tipula paludosa, which frequents marsh land. There are many species of Tipula in other parts of the world, and there are closely allied kinds which are ranked in distinct genera, differing a little in certain features from the genus Tipula. These all form, taken together, the family Tipulidæ. They, together with the various kinds of gnats or "mosquitoes," the midges and fungus-flies, form one of two divisions into which the two-winged insects or Diptera are divided, namely, those with long, thread-like feelers or antennæ (Nemocera—thread horned), the other division being those with quite short antennæ (Brachycera—short horned). The latter group comprises the flies with thick, heavy bodies, such as the common house-fly, the bluebottle, the horse-flies, bott-flies, and tsetse-flies. The long-horned group have usually long, narrow bodies and long, narrow wings, which do not at once lie flat on the back when the fly alights (as do those of the short-horned group, as, for instance, those of the common house-fly). The females of the common gnat (Culex pipiens) and numerous allied species are bloodsuckers. The various midges are mostly harmless, whilst others have females which suck blood. The crane-flies do not bite. The real feeding of all these gnat-like flies is done when they are in the grub phase of their life, but the females of some gnats and midges appear to have the need of extra nourishment when in the fully-formed free-flying state, in order to ripen their large bulk of eggs. Hence, in some cases, they (but not the males) suck the juices of plants and the blood of animals.
The larval or grub phase of life is passed by many of these flies in the earth amidst putrefying vegetable and animal refuse on which they feed, as in the instance of the daddy-long-legs; but here and there we find species which penetrate into the soft parts of plants and animals. A whole group of many species burrow into mushrooms and other fungi when they are grubs; others, again, live in water when they are grubs or "larvæ," and have a very active aquatic life, rising to the surface to breathe air and searching for food in the water with their feelers and eyes, and seizing it with their powerful jaws. The mother fly in these cases lays her eggs in a group on the surface of the water or embedded in a jelly which she secretes and attaches to the leaves of water plants. Some of the short-horned flies (bott-flies and others) lay their eggs in the living flesh of warm-blooded animals, including man, and the maggots hatch there and feed on the juices of the "flyblown" animal. Cases are not rare of children being thus infested.
The black flies which fly in swarms "high" or "low" in the country lanes on summer evenings are not true biting gnats, but a large kind of midges known as Chironomus or Harlequin flies. Their eggs are laid in the water of ponds, and the larvæ on hatching bury themselves in the rich black mud and feed there. The larvæ are of a splendid blood-red colour, and are often called "blood-worms." They owe their colour to the presence in their blood of the same red oxygen-seizing crystallizable substance, hæmoglobin, which gives its red colour to the blood of man and other vertebrates. Its presence is remarkable, because in all other insects the blood is colourless or of pale blue or green tint. It seems that this hæmoglobin renders service to the larvæ of the big midges as it does to some other creatures which live in impure water, where free oxygen is very small in quantity, namely, it enables them to absorb and hold by loose chemical combination the small quantity of oxygen available. The minute midges called "Hessian fly" and "Cecidomyia"—injurious to cereal crops—should be mentioned here as among the allies of crane-flies, as also the blood-sucking midges, Ceratopogon, and the minute blood-sucking sand-flies or Buffalo-flies, called "Simulium." Species of Ceratopogon, so minute as to be barely visible, cause terrible annoyance by their bites to the salmon-fisher in Scotland, where they often swarm in countless numbers. The Buffalo-flies attack man, but in some districts of North America alight in thousands on cattle, and cause death in a few hours. A harmless long-horned fly is "the plumed fly," Corethra, the large aquatic larva of which is glass-like and quite transparent, and offers splendid facilities for microscopic research. I used to take it every year in a pond near Hampstead Heath.
The leather-jackets, or grubs of the common crane-fly ([Fig. 22, B]), sometimes destroy hundreds of acres—even whole districts—of grassland in England and France by gnawing the young subterranean roots and shoots of the grass. They also destroy young wheat crops. The leather-jacket is regarded by agriculturists as an intractable pest, since it gets too deep into the turf to be destroyed by chemical poisons. Its thick skin also makes it very resistant to such treatment. When immersed in brine for twenty-four hours the grubs are not killed; prolonged immersion in water is equally ineffective; they may be frozen until they are brittle, and will yet recover; and when kept three weeks without food, still remain alive. Birds are their natural enemies, and rooks not only dig after the grubs, but swallow the flies at the rate of four a minute! Ploughing up the land in which the grubs abound is recommended as a means of destroying them, and also the application of gas-lime to the ground. Rolling the turf and pressing it down also kills the grubs, but the best chance of diminishing their ravages is found in draining wet land and in feeding up the young grass plants with "fertilizers," so that they may grow rapidly and resist the injurious effect of the leather-jackets' nibbling.
Before leaving this subject it will be found interesting to contrast the "leather-jacket" with the true "wire-worms," which are the grubs of a remarkable kind of beetle (there are half a dozen British species) called the click-beetle ([Fig. 22, C]). They belong to a great family of beetles (Coleoptera), known as the Elaterids or Elaters, of which 7000 species are known, sixty being British. Some of the most brilliant light-giving or phosphorescent insects (not, however, the common glow-worms) belong here. The click-beetles are so called because when one is laid on its back it regains its proper pose, with the legs beneath it, by a spring or "skip," accompanied by a sharp click. The grubs of the click-beetles, known as "wire-worms" (the name is also applied to centipedes), are more threadlike, that is to say narrower, than the leather-jackets. They are not legless "maggots," but have three pairs of small legs ([Fig. 22, D]). They destroy corn and grass, and do not change into the adult condition in a few months, as do the leather-jackets, but remain for three, and in some cases five, years in the ground feeding on the roots of the corn and grass plants, doing much destruction before they finally change into beetles.