DIPTERA OR TRUE FLIES. 211 



extremity, and are leecli-like in movement. They pupate on the 

 leaves where they have been feeding in globular cases or puparia 

 (fig. 103, 3 and 6). The typical genus is Syrplrus, of which 

 there are a great number of species found. Most have broadish 

 flat abdomens, often almost transparent, with yellow and black 

 hands, and extremely delicate pale-coloured legs. S. rihesii and 

 8. halteaiiis are perhaps two of our commonest species living on 

 plant-lice. 



Other genera are parasitic ( Volucella), living in the nests of 

 Humble-bees (V. lioriihylana) and Wasps {V. zonaria), when 

 they mimic the colour and appearance of the insects they live 

 amongst. 



Warble-flies, or (Estridse. 



This family of flies is most obnoxious to our domestic and 

 wild mammals, upon which they live as parasites during their 

 larval period. The larvfe arc called " bots,'' and live under the 

 skin, in the head, and in the stomach and intestines of animals. 

 The most injurious species are the Ox-warbles (Hypoderma 

 hovis and H. lineata), the Sheep jSTasal-fiy [CEdrus ovis), and 

 the Horse-bot {Gastrophilus equi), which we will deal with in 

 the above-mentioned order. 



Ox-WARBLEB OB BoT-FLY (HyPODERMA BOVIS AND H. LINEATa). 



These two species, which are very similar in appearance, at 

 one time caused serious loss amongst 

 beasts : the annual amount, according 

 to Miss Ormerod, was something like 

 £7,000,000. But, thanks to her great 

 energies, this serious malady has been 

 checked, although it still does a great fio. lo*.— Ox-warblb 



{Hypoderma boL'is\ 



amount of harm. The Ox -Warble fly 



(fig. 104) is like a small hairy humble-bee in appearance, gaily 



coloured with thick hair of yellow, black, and red bauds on the 



