TENTHREDO, the SAW-FLY; a genus of insects belonging to the order of hymenoptera. The mouth is furnished with jaws, but has no proboscis; the wings are plain and tumid; the ring consists of two serrated laminae, and the scutellum of two grains placed at a distance. The species are very numerous, differing from one another in colour and size. They are not very shy. Some, by means of their saw, deposit in the buds of flowers, others on the twigs of trees or shrubs, eggs from which are produced false caterpillars. The implement with which they are armed is nowise formidable; as it appears only destined to the purpose of depositing their eggs.
The sylvatica is a beautiful species. The antennæ are setaceous, and have more than 20 joints. The head is blue; the trunk grey mottled with yellow; the body is black; the lines dividing the rings are brownish; the six terminatory segments are amber-coloured. The wings are brown, with a dusky edge. The legs are yellow. This delicate fly is found in damp woods and moors in August and September. When the female lays her eggs, there goes with them an acrid mucilaginous juice, which perverts the course of the sap in the plant, and makes it grow into a kind of gall; this operates as soon as emitted, and scarifies the part the saw has wounded. One may see bubbles of this soft and clammy juice always left upon the plant; the wound is oblong and crooked, and the part becomes black as if burnt. The egg increases in bigness to twice its size, or more, after it is lodged in the plant; nor is this strange, since it has no hard covering. The larvae may easily be known by the number of their feet, which are always more than 16; by which they differ from caterpillars, which have 16 at most, and
never fewer than 8. In order to accomplish their metamorphosis, they hide themselves in the ground, spin their cocoon, the inside of which is lined with a very fine down, and admit through the netted texture that moisture from the earth which they have need of in the state of chrysalids.