SCIENCE-GOSSIF. 



97 



FLIES PEOPEK. 



By Walter Wesche. 



"OST people with a taste for natural history 

 ■*-'-^ collect something. The majority, attracted 

 by the beautiful appearance of a neatly arranged 

 case of the lovely insects, prefer butteriiies and 

 moths ; some collect beetles, and a still fewer 

 number are interested in flies, or, to be more pre- 

 cise, the Diptera. 



In the case of most dwellers in cities the idea 

 of a fly is formed by a distant acquaintance with 



Fig. 1. Diagram of House Fly. 



the house fly, and associated with the annoyance 

 •caused by that persevering insect on summer days. 

 As to variety, small and large would be sufficient 

 ■definition, though some people might plead guilty 

 to calling the larger " blue-bottles." Even a 

 •countryman knows little about them, though you 

 may hear him speak of hawk- or hover-iiies. It 

 would be quite a matter of surprise to learn that 

 the familiar daddy-long-legs or crane-fly, mos- 

 ■quitoes, and gnats are all made on similar lines, 

 -and belong to the same order as house flies. 

 Further, that there are above 3,000 species in the 

 Eritish Isles. It is obvious that there must be 

 plenty of variety, and that this variety will require 

 more than cursory examination. 



The chief characteristic of Diptera is that they 

 ■have only two wings, and another is the "balancer," 

 or " haltere," a little rod with a clubbed end, 

 which will be noticed at the base of the wing 

 (fig. 3). It is supposed to be the rudiment or else 

 the atrophied remains of a second wing. It can 

 Tdb seen with the naked eye ; but in small insects, 

 like the majority of flies, a lens is useful ; and if all 

 the most interesting and complicated detail is to 

 ^be made out, a powerful microscope is necessary. 



If we examine the diagrams of a house fly and 

 a crane fly (figs. 1 and 2) we shall see that an 



SEPTEMBER 1901.— No. 88, VoL. VIIlT. ] 



insect is a far more complicated piece of mechanism 

 than a mammal ; but even then in these diagrams 

 there is a vast amount of detail left out : all the 

 mouth organs are hidden, the antennae only partly 

 show, and the immense numbers of spines, bristles, 

 and hairs, which are modified in many different 

 ways for various purposes, are not even indicated. 



In fig. 4 I have attempted to show what the 

 head of a fly looks like, but the proboscis is drawn 

 diagrammatically to exhibit the position of the 

 different contrivances with which it i sfitted : viz. 

 the palpi, or feelers, and the lancets, hidden in the 

 sharp cover or case which projects. Above that is 

 one of the palpi covered with short hair and spines, 

 and one of the levers Avhich work the lancets, 

 shows to the right. At the end of the proboscis 

 are the well-known tubes through which the fly 

 sucks up its food, and at their base are some little 

 teeth (fig. 5) with which it scrapes, scratches, 

 and breaks up matter to a size that will pass up 

 the tubes. It is interesting to find that in those 

 flies feeding on pollen these teeth are absent, 

 the size of the tubes being adapted to the pollen 

 fed upon, which is sucked up whole. The lancets 



Fig. 2. Diagraji op Crane Ply. 



are used as an offensive weapon, and in those flies 

 which live on other insects are used to kill the 

 prey, the insect being guided in their use by the 

 two palpi. The eyes are very large and com- 

 pound, and contain about four thousand facets, or 

 separate eyes. Besides this, to enable the insect 

 to see above and behind, the head has on the crown 

 three simple eyes. The compound eyes of the 

 male are, as a rule, larger than those of the female, 

 enabling him to see with greater ease, and of 

 advantage to him in his search for a mate. 



In front of the head are the antennae. The 

 use of these organs was long a mystery, but it 

 now seems fairly demonstrated that they are for 

 Published August 26th, 1901 



