How they become aware of their surroundings 



Fig. 44. At the other 

 extreme of the Order 

 Diptera is this 

 warble-fly, stout and 

 hairy 



Sometimes the area of thin cuticle is still visible as a hair : sometimes 

 this hair is recessed in a pit, or in a bulb at the end of a long stalk; 

 sometimes there is merely a flat area {pore-plate) on the surface of the 

 body (Figs. 38, 42). Olfactory hairs are mainly found on the legs (tarsi) 

 and on the proboscis; olfactory pits on the palpi and antennae; and 

 pore-plates on the antennae. 



Imms (1957, p. 96) hsts four principal ways in which the sense of 

 smell is used by insects. 



1. Sexual attraction. The 'assembling' of male moths to a virgin 

 female moth is a well-known phenomenon. The males show the same 

 reaction to certain pure chemicals, though there is as yet no evidence 

 that female moths actually produce these particular chemicals. 



2. Recognition odours. Ants and bees can recognise the odour of 

 their own species : ants follow trails laid down by other ants, and are 

 temporarily confused if you rub a finger across the trail; bees recognise 

 and fight invaders from other nests. It has been suggested that the reason 

 why hibernating flies come into the same house year after year may be 

 that the swarms leave an odour behind them. 



3. Oviposition attractants. It is well known that a great many insects 

 are attracted by smell to a place suitable for egg-laying: e.g. blowflies 

 to meat. Here again there is the fact that pure chemical odours attract 

 insects even though these substances do not occur naturally: e.g. 



69 



