608 INSECTA ORDER DIPTERA. 



The house-fly is most common in summer and autumn, but there are other 

 flies very similar to it in size and colour, belonging to the sub-family Antho- 

 myince, which are common in houses earlier in the year, and are commonly 

 called house-flies. It is perhaps hardly necessary to say that although many 

 genera and species of flies are common in houses, either habitually or casually, 

 none of them ever grow after assuming the perfect state ; and it would, con- 

 sequently, be an absurd error to suppose that the small flies are the young 

 of the large ones, even though individuals of the same species may vary a 

 little in size within narrow limits. 



Other larger flies are common in our houses, with brown bodies and blue 

 or purple abdomens. They are generally called blue-bottle flies, and their 

 grubs feed on meat, or carrion. A smaller and prettier species, the green- 

 bottle, Lucilia ccesar (Linn.), is more frequently observed out of doors. 

 Linnaeus is reported to have said that the progeny of three blow-flies could 

 devour the carcass of an ox as quickly as a lion could. The Tse-tse fly, 

 Glossina morsitans (Westwood), which destroys horses and cattle in South 

 Africa, is another species of this sub-family ; it is about the size of a bee. 



MUSCID.E ACALYPTER.E. 



This is another large section, divided into several sub-families, mostly of 

 small size. Some of them feed on dung, like the conspicuous yellow fly, 

 Scatophaga stercoraria (Linn.); others, as the sub-families, Ortalince, Trypetince, 

 and Agromyzince, feed on plants ; some in the heads of floweTs, and others 

 mining the leaves of trees, like the Tinece among the moths. Most of the flies 

 of this section are small and slender, and many have very prettily variegated 

 wings. The best known species is perhaps Piophila casei (Linn.), a rather 

 slender, black, hairy fly, the larvae of which feed on cheese or bacon. It 

 belongs to the sub-family Piophilince. 



Fig. 103. SWALLOW FLY Fig. 104. SHEEP TICK 



(Ornithomyia avicularia, (Mallophagus ovinus, 



Linn.). Nat. size. Linn.). Nat. size. 



DIPTERA HOMALOPTERA. 



This section contains only two families, the Hippoboscidce and Nycteribiidw, 

 which include a few species with a rather horny integument, and very hairy, 

 sprawling legs. They are parasitic on various mammals and birds ; and 

 some of the species, such as the sheep tick, Melophagus ovinus (Linn. ), are 

 apterous. 



