How they become aware of their surroundings 



Fig. 47. This bee-fly. Order Diptera, feeds from primroses in the spring 



sea-weed flies are irresistibly attracted by trichloroethylene which, 

 though somewhat related chemically to the halogen compounds in sea- 

 weed, is not a natural odour. 



4. Food attractants. Very similar to oviposition attractants, and in 

 some cases — e.g. dung inseas — it may be difficult to say which is the 

 more important basis of attraction. 



The sense of taste in insects has been studied by off"ering them 

 substances that taste sweet, sour, salt or bitter to us, and seeing their 

 reactions. In this way it is possible to tell which substances they are 

 able to distinguish from each other, and whether they like them or 

 not. Honey-bees are specially suitable for this kind of experiment, 

 because they are domesticated insects, and a great deal is already 

 known about their way of life. As might be expected, bees are par- 

 ticularly discriminating in their tasting of sweet substances, and will 

 reject not only artificial sweeteners such as saccharin, but also many 

 true sugars that seem reasonably sweet to the human palate. 



The chief organ of taste is the mouth, but insects may also have 

 taste-cells in the antennae and in the tarsi of the legs. These organs are 

 used to make a prehminary inspeaion of their surroundings, and many 

 insects will at once extend their proboscis if their tarsi come in contact 

 with a sugar solution. 



71 



