74 Searle, Gleanings of a City Naturalist. [vo["xxxv 



house-fly, is only a very occasional visitor. The common 

 yellow blow-fly, Calliphora villosa, is far more numerous, and 

 the dark blue one, C. erythrocephala, a frequent visitor. 

 When attempt is made to capture these annoying insects, the 

 yellow fly, after buzzing excitedly around the office, attempts 

 to escape through the window-pane, on which it is easily 

 captured and exterminated ; but the slower-flying blue insect, 

 C. erythrocephala, will invariably fly to some dark corner near 

 the floor or behind some object, and immediately rest there 

 until it thinks the danger is past, when it will again emerge, 

 only to repeat these tactics if again pursued. It may be of 

 interest to note the change in the breeding habits of some of 

 these flies. Formerly they deposited their eggs or larvae on 

 some dead animal, the " higher " and more " gamey " the 

 better, though not averse at times to a fresh joint of butcher's 

 meat or poultry ; but of late years they have developed into 

 a great pest, since they acquired the habit of breeding in the 

 thick greasy fleece of living sheep. Enormous sums of money 

 have been spent, and is still being expended, in trjdng to 

 eradicate this pest. 



When Miisca domestica visits the office it flies directly to the 

 window, and appears to be as anxious to again leave as I am 

 for it to go. Smaller diptcra of elegant forms — many, perhaps, 

 undcscribed — are to be seen occasionally on these same 

 windows, and on two occasions immense clouds of very minute 

 flies invaded the city and filled every office. On one occasion, 

 I remember, a building had been newly painted w^hen an 

 invasion of these tiny flies occurred, and in a short time the 

 front of the building was ornamented with millions of these 

 insects, which had stuck to the fresh paint. Mosquitoes and 

 Chironomus are found occasionally, and two or three crane- 

 flies were captured. 



The structure of a dipterous insect is very remarkable, and 

 the material collected in my office was sufficient to keep a 

 naturalist busy for many months examining their micro- 

 anatomy. As an example of what the city naturalist may 

 find to interest him in a dipterous insect, wc will glance briefly 

 at the anatomy of one of the commonest — the house-fly. 

 In examining a fly we notice at once that it is divided inta 

 three parts — the head, thorax, and the abdomen. The head 

 contains the eyes and mouth parts, the thorax the organs of 

 locomotion, and the abdomen the digestive system and the 

 reproductive organs. The head is connected with the thorax 

 by a slender neck that permits it to undergo semi-rotation. 

 We observe that its greater part consists of a pair of hemi- 

 spherical compound eyes, made up of a number of small facets 

 — over 4,000 have been counted; each facet consists of a 



