98 



SCIENCE- G OS SIP. 



smelling, and also in some degree for a sense of 

 touch, the long bristle being obviously for this 

 purpose. This bristle in the house fly is like an 

 aigret, and is plumose, as the entomologists call it. 

 It is a curious thing that insects should breathe 

 through their backs, and not only breathe, but 



Fig. 3. " Balancer" or " Poiser" of Midge. 



make sounds. Under the outer shell, which is 

 horny, are a vast number of minute tubes that 

 practically are the lungs of the insect. This fact 

 may be demonstrated by placing a drop of oil on 

 its back, when it instantly dies, being suffocated. 

 These tubes have little openings in the back, 

 known as spii'acles : they will be noticed on the 

 diagram (fig. 1), two to each joint of the abdo- 

 men. At the base of the fore legs will be observed 

 two of a pear shape, and it is through these that 

 sound is produced. My impression is that it is 

 only made when the insect is in distress or pain, 



Fig. 4. Diagram o£ side of head of House Fl.y, showing tlie 

 position of the eyes, antenna, palpus, lancet, and lobe 

 of the proboscis. 



though I have noticed a Syrphus-fly, one of the 

 pollen feeders I referred to just now, making 

 quite a musical note while walking on a window- 

 pane. The wings, that make 660 simple oscilla- 

 tions in a second of time, also produce sound, 

 which is, however, quite different from that 

 emitted through the spiracles. 



The shell of insects is formed of a substance 

 called chitin, which is horny and not sen.sitive to 

 touch. To repair this defect the body 

 is in many instances covered with a 

 quantity of spines and hairs, that 

 act as nerves and enable the fly to 

 feel the approach of danger and to 

 have the sense of contact, which 

 otherwise would be absent. To keep 

 all these hairs clean and free from 

 dust and dirt, brushes are necessary 

 (fig. 6), and these will be found on the legs. Any- 

 one who has watched a fly during the careful 

 cleaning of his body with the hind legs, and of 

 his head with the fore legs, will readily under- 

 stand this. 



As most of us know, flies will feed on almost 

 anything ; but there are many families who are 



cannibals, thriving on their fellow-flies. Fig. T 

 shows the shape of one of these — a little insect less 

 than two lines in length. It has no popular name,, 

 so I have to give the scientific, which in length is in 

 inverse ratio to the size, being Tachydromia arro- 

 f/ans, or the arrogant Tarliyclromia. The middle 

 legs are remarkable : they are furnished with rows 

 of teeth to enable the insect to grip and hold the 

 wings while the sharp-pointed tibia is dug into the 

 side of the victim. The head is furnished with 

 lancets for piercing, and trachae for sucking blood. 

 One of the most curious and interesting things: 

 in insects is what is known as " mimicry " ; that is, 

 a modification of its appearance through the pro- 

 cesses of evolution, so that it resembles either ars 



Fig. 5. Expanded lobes of proboscis of House Fly, showings 

 arrangement of tubes and position of teeth. 



inanimate substance, as a leaf or twig, or some 

 other insect which is better capable of defending' 

 itself, or is in some way objectionable to other- 

 animals, perhaps to the taste or the smell. 



There are many flies, wliicli to the unpractised' 

 eye are easily mistaken for wasps or bees, thatr 

 we well know have stings and poison-bags. I re- 

 member my first capture of Erystalis fenax, a; 

 harmless fly that mimics a bee. It buzzes like- 

 an angry one, and moves its abdomen up andl 

 down in a manner most suggestive of being fur- 

 nished with a particularly sharp sting. As a 

 matter of fact, it is a profound humbug, but like 

 many humbugs it succeeds, or at all events has a 

 mea,sure of success, for I was most desperately 

 cautious with it, and quite convinced I had caught 



Pig. 6. Fore Leg of House Fly, showing arrangement of hair used in cleaning 

 head and proboscis. 



an insect who only wanted opportunity to sting 

 severely. The popular name is the bee- or drone- 

 fly : it feeds on pollen, and its larva is known as the 

 " rat-tailed maggot." This lives in water and has 

 a most wonderful telescopic tail, that it pushes up 

 to the surface and by which it breathes. There 

 are some flies of the family Bombylidae that are 



