Nematus
A very large genus of Tenthredinidae, or Sawflies, of much importance because of the harm done by the larvae to various trees and shrubs, but especially to Willows, Gooseberries, and Currants. They are the type of a sub-family, Nematina, that has the larva provided with fourteen sucker feet. In this sub-family it is distinguished from the other genera by the form and arrangements of the nerves of the front wings, and of the cellules formed by them. The insects are never large, and they bear so great a likeness to one another that it is most difficult to distinguish the species, since they are mostly smooth and shining, are seldom, if ever, punctured, and do not vary in pubescence. By their colour, the species may be divided into groups: (1) Abdomen wholly black; (2) abdomen banded with red; (3) body black and yellow; (4) body wholly yellow, or slightly marked with black; (5) body green. These groups, however, grade into one another. Mr. Cameron, in his work on British Sawflies, says that there may be 400 species of this genus in Europe, and he describes 107 from Britain alone. The larvae vary much in habits. Some are gregarious, while others are solitary; most feed exposed, but some roll up the edge of the leaves, to form a tube, in which they live; and others form pea or bean-shaped galls on the leaves of Willows. Indeed, few kinds of these latter plants are entirely free from their galls; while on some bushes almost every leaf is loaded with them. The larvae, when full fed, generally burrow an inch or two into the soil, and there form cocoons. The pupae are usually green, often with a mixture of orange. It is impossible here to enumerate all the trees and bushes that are attacked by the larvae; but a few of the more important are described. Gooseberries are ravaged by N. Ribesii, N. appendiculatus, and N. consobrinus; N. abbreviatus feeds on Apples and Pears; several kinds feed on Alder, others on Birch; very many are to be found on Willows of all species. Of the Willow Sawflies, the following are gall-makers: N. vesicator, in bean-shaped galls in the leaves; N. ischnocerus, in rather long galls, in pairs along the midribs of the leaves; N. baccarum, N. salicis-cinereae, and N. bellus, in pea-shaped galls on the lower surface of the leaves of various Willows; N. herbaceae, in similar galls on Salix herbacea; N. gallicola, in the bean-shaped galls so plentiful in leaves of Salix alba and other large Willows; and N. Bridgmanni, in similar galls from Sallows; N. Vacciniellus forms galls on Vaccinium Vitis-idaea. For methods of checking the ravages of such larvae as feed exposed, see Gooseberry and Currant Sawfly.