TRACHEATA 373 
long slender legs. The mesonotum bears a V-shaped mark, 
and the abdomen is long and cylindrical. Their larvae burrow 
underground, and do considerable damage to crops by gnawing 
roots, etc. They are known as leather-jackets, and are of a 
whitish-brown colour and grub-like appearance. Z%pula oleracea, 
T. maculosa, and T. paludosa are all common English species. 
Family CECIDOMYIIDAE (gall - flies)—This is a family of 
small Diptera, which give rise to galls in plants. Their wings 
have few nervures, usually three longitudinal ones; they are 
rounded at their free ends; the point of attachment is, how- 
ever, very narrow. The antennae have numerous joints, and 
are moniliform. The proboscis is short and the legs long. The 
females have a well-developed ovipositor, by means of which they 
puncture some plant and deposit their egg therein. This in 
some cases gives rise to a gall, in which the larvae develope. 
The pupa stage may also be undergone in the gall, or it may 
Fic. 210.—Cecidomyia destructor 
(the Hessian-fly). 
1. Insect. 
2. Larva, 
3. Pupa or ‘flax seed.” 
All magnified. 
be free. The larvae of some of the Cecidomyias produce 
parthenogenetic ova, from which young are born, a phenomenon 
known as paedogenesis. Cecidomyia destructor is the well- 
known Hessian-fly. (. salicis produces galls on willows. 
Family TABANIDAE (horse-flies).— Tabanus is the horse-fly, 
a large Dipterous insect. The male does not bite, but lives on 
the nectar of flowers. The bite of the female, however, is 
very painful and poisonous. Cases have been recorded of horses 
on the prairies being worried to death by these insects. The 
larvae of Zabanus are said to live upon snails, those of allied 
genera live in water. 
Family BompyLipar.—Very hairy flies, swift in flight, 
