5 FLIES FOUND IN HOUSES 



The Order Diptera is composed of insects possessing two 

 membranous, usually transparent, wings. Behind the wings is 

 placed a pair of small stalk-like bodies terminating in small 

 knobs— the halteres — frequently concealed beneath membranous 

 hoods. The mouth parts are formed for sucking. The meta- 

 morphosis, or series of changes undergone during development, 

 is very great, the larvae or young forms which develop from eggs 

 bearing no resemblance whatever to the perfect insects, being 

 usually footless grubs or maggots. 



The Order is divided into two Sub-orders, the Cyclorrhapha 

 and the Orthorrhapha. The nature of the metamorphosis 

 differentiates these two groups. In the Cyclorrhapha the larva 

 does not escape from the larval skin at the last moult but 

 shrinks within it, so that the larval skin, itself contracted and 

 altered by an excretion of chitin, remains and forms a perfect 

 protection for the enclosed organism or pnpa. Such a pupa is 

 described as coarctate, and the brown skin is called \hQ. pitparium. 

 This puparium, which is barrel shaped, has no marks except 

 some faint circular rings and frequently a pair of projections 

 from near one extremity. This sub-order is again divided 

 into the Aschiza, in which the front of the head of the perfect 

 fly shows no definite arched suture over the antennae, and the 

 Schizophora in most of which the frontal suture (see Fig. 2) is 

 well marked and extends downwards along each side of the 

 face, leaving a distinct hnuUe over the antennae. Most of the 

 important non-biting disease carrying flies belong to the latter 

 group. 



In the Orthorrhapha the pupa is a mummy-like object, or 

 pupa obtecta, in which there is a crisp outer shell, formed in part 

 by the adherent cases of the appendages of the future fly. 



TJie external features of a fly. 



In most of the flies considered in this book the bod\- is 

 composed of three easily recognizable divisions, termed respect- 

 ively, head, thorax and abdomen. 



The head, which is remarkable for its mobilit}', is connected 

 with the thorax by a slender neck that permits the head to 



