Wireworms
The popular name of certain pale yellowish-brown, slender larvae, possessed of skins so tough and hard that they look and feel not unlike short pieces of moderately thick wire, flattened from above downwards. The body is of uniform thickness, and is marked with rings showing the divisions between the segments of which it consists. The head is small, flattened, and darker than the body. The three front body-rings bear each a pair of short, brown, true legs, and there is a solitary prehensile foot on the lower surface of the conical hindmost segment of the body. Wireworms feed near the surface of the soil, but concealed in it; and they gnaw the stems and roots of plants just below its surface. The plants are thereby killed, or, at least, very much injured; and the crops in gardens, as well as in the fields, are, occasionally, seriously damaged from this cause. When the Wireworms reach their full size, they burrow into the soil to a considerable depth, and each forms for itself an earthen cocoon. In this it becomes a pupa, usually about the end of summer. Many of the Beetles emerge after spending little more than a fortnight in the pupa state, but some, probably, do not emerge till the next spring or summer. Wireworms vary in size to some extent, as they are the larvae of many kinds of Beetles, all belonging to the family Elateridae, but they seldom reach 1in. in length. They feed on almost all kinds of herbaceous plants, but it has been observed that they avoid Mustard: hence it has been suggested that this plant should be sown in ground that is much infested by them, in order to starve them out.
The Beetles are well known under one or other of the names Click Beetle, Snap Beetle, Spring Beetle, or Skipjack. All four names allude to the method by which the insects, when laid on their backs, right themselves, and which is described below. There are many species of Click Beetles distributed amongst numerous genera, which differ among themselves in minor peculiarities; but all of them have so strong a family likeness that they are easily recognised as members of the family Elateridae. Their form is elongated, with nearly parallel sides, but the body is rather pointed behind; the surface is hard. The head is deeply sunk in the thorax; the latter is prolonged backwards at the hinder angles into two sharp points, which prevent lateral movements of the abdomen; it has a sharp, prominent spine on its front part below, and this spine fits into a groove in front of the base of the middle legs. The antennae, which are often serrated, can be laid, for protection, into grooves on the lower surface of the head-one on each side. The legs are short, but the wings are large and powerful. The Beetles are usually black, often with the basal tow-thirds of the elytra some shade between rusty-red and blood-red, less often with short, fuscous or yellowish hairs spread uniformly over the surface, or restricted to defined spots or patches. They seldom exceed 3/4in. or fall below 1/5in. in length. The number of British species of this family is large, and the Beetles are abundant everywhere during autumn; but only a few of the species are large enough to be familiarly known by anyone except an entomologist. They may be often seen crawling on walls and among herbage. When approached, they allow themselves to drop for concealment; and their form renders them very liable to fall on their back. Their legs are too short to be of service in turning themselves over; but the spine on the breast is an efficient organ for this purpose. When one of the insects wishes to replace itself on its legs, it bends the body backwards till it rests only on the head and the tip of the abdomen. In this position the spine is dragged out of its groove, but, on the Beetle bringing the head up smartly, the spine springs back into its groove, and the back of the Beetle is struck so hard against the surface on which it lies, that the insect is thrown some inches into the air, like a skipjack, and usually falls on its legs. The names Skipjack and Spring Beetle refer to this power of leaping; Click Beetle and Snap Beetle refer to the sound produced in the leap. It is probable that the larvae of almost all of the Elateridae are Wireworms in appearance and in habits; but only a few of the species are known to be very injurious to garden and field produce; and some, at least, feed on decaying vegetable tissues.
The following are the most hurtful species, according to the observations of those entomologists who have most carefully studied the subject: Agriotes sputator, A. lineatus, and A. obscurus. The first of these is little more than 1/4in. long, and is black, and slightly glossy, but is pubescent; the front edge and hinder angles of the thorax, and the greater part of the elytra, are dull yellowish-brown or dusky; the legs and antennae are paler; the elytra are deeply punctate-striate. The other two species are about 1/3in. or 3/8in. long, and are thought by some to be forms of a single species. A. lineatus is fuscous, with greyish pubescence; the thorax is nearly black; the elytra are punctate-striate, the striae (in pairs) greyish, the interspaces brown, so that the elytra are striped length-wise with dull grey and brown; the limbs are rusty-red. A. obscurus is dull brown-black, with dark pubescence, the elytra faintly punctate-striate, and nearly black; the thighs are nearly black, the rest of the legs and the antennae dull rusty-red. Still another species is probably a serious foe to cultivated plants at times. This is Athous haemorrhoidalis; the insect is from 1/2in. to 2/3in. long, and is dusky-black, with the elytra brownish; the limbs are dull red, except the black thighs. In the perfect state these insects are harmless: the damage is done only in the larval condition. This stage has been observed to continue in A. lineatus during five years; hence, the larvae have time to do much mischief. It would be useless to enumerate all the plants on which they have been observed to feed; but among the more important garden plants are Cabbages, Carrots, Dahlias, Irises, Lettuces, Onions, Pinks, Potatoes, Turnips, and other favourites. They also often seriously injure the grass in lawns. Where ground is allowed to lie unbroken for a time, they multiply, and from it they spread to the adjoining pieces of ground. When soil that has lain fallow, or has been a lawn for some years, is broken up, the crops grown in it are apt to suffer severely from attacks of Wireworm. Remedies. When the larvae are very numerous, the soil should be broken up, as this exposes the Wireworms to the eyes of birds. Deep-trenching has also been recommended as a useful measure. If practicable, one of the most successful methods is to starve out the larvae by allowing the ground to lie fallow for a year, merely cutting down and destroying the weeds on it; or a crop of Mustard (Brassica alba) may be grown on it, as the larvae avoid this plant. Frequent stirring of the soil is unfavourable to them; and so, to a slight extent, is the employment of a heavy roller. Various applications to the soil have been used with success. On ground allowed to lie fallow for a year, a good coating of fresh gas-lime is of great use; but where crops have to be grown without a break of this kind, soot and guano are better, scattered before or during heavy rain. One part of nitrate of soda to two of common salt has also worked well. In gardens, paraffin has been used in solution (one in fifteen) with success, for watering infested plants, or along drills of Carrots, &c. Where any plants are fading without apparent cause, the roots should be examined for Wireworms, and one of the remedies recommended above should be applied to the injured plants. Traps for Wireworms, formed of pieces of lettuce, carrot, or other favourite food, may also be used. These should be buried a little below the surface, and removed, examined every day, and the Wireworms on them collected and destroyed.