THE CLASSIFICATION OF INSECTS 93 



floats in the water, or is enveloped in a puparium formed 

 from the last larval skin. There are two sub-orders, both 

 of which include many families. 



Sub-Order 1 . — Orthorrhapha. 



In this sub-order the larva has a hard head, while the 

 skin of the pupa or puparium splits longitudinally down 

 the back, allowing the perfect insect to escape. There are 

 a large number of families which fall into two groups. 



In the first group the antenna? are slender and thread- 

 like, and relatively long. It includes, among other families, 

 the gall-midges (Cecidomyidce), whose larvae burrow into 

 plant tissues and often give rise to galls ; the fungus- 

 midges (Mycetophilidce), whose larvae feed in vegetable 

 refuse and fungi ; the true midges {Chironomidce), and the 

 gnats {Culichke), whose larvae are aquatic. The family of 

 crane-flies or dadd}^-longlcgs (Tipulidce) also belong to 

 this group. Their larvae — well known as " leather-jackets " 

 — feed upon the roots of plants and are notorious pests. 



In the second group of families the antenna? are rela- 

 tively short, usually with only three segments. Among 

 them are the gad-flies (Tabrmidce), the females of which 

 suck the blood of horses and cattle, although the larva? 

 live in damp earth, and feed upon snails, slugs, and beetle- 

 grubs. The larva? of the robber-flies {Asilidce) also live 

 in damp earth, while the imagines prey upon other 

 insects. The bee-iiies (Bombyliida') resemble humble- 

 bees in appearance, and suck nectar from flowers. Their 

 life-histories are imperfectly known, but in some species 

 the larvae are parasitic upon bee-grubs, while others devour 

 the eggs of locusts. 



