INSECTS 



241 



objects the keenness of vision and especially the distance at which a flj 

 notices movement of an object. 



Feed the fly with a drop of sugar solution. Study the movement of the 

 organ called the proboscis. This proboscis is made up chiefly of the maxillsE, 

 together with the labial palps, the mandible being undeveloped. P'ood is 

 obtained by lapping and sucking. Notice the flaplike extensions on each 

 side of the proboscis; these are roughened on the under surface. It is the 

 rubbing of this filelike organ over the surface of the skin that causes the 

 painful bite of the horse fly. If possible, examine the foot of a fly under a 

 low magnification of the compound microscope. The foot shows a won- 

 derful adaptation for clinging to smooth surfaces. Two or three pads, each 

 of which bears tubelike hairs that secrete a sticky fluid, are found on its 

 under surface. It is by this means that the fly is able to walk upside down. 



Home Experiments. — Test the keenness of scent in the fly by placing in 

 an exposed place a bit of meat, some bread, salt, sugar, and other foods, 

 some of which have distinct odor. Cover each food with tissue paper. 

 Which food attracts the most flies ? 



Test the sense of taste of the fly by the following experiment. 



Place in a netting cage four butter chips containing a solution of sugar, 

 salt, alum, and strychnine or other bitter fluid. Place in the cage a number 

 of flies, and at the end of a given period count the number at each dish. Do 

 flies appear to have the sense of taste ? 



Life history of house flies, showing from left to right the eggs, larvao, pupae, and adult flies. 



Photograph, about natural size, by Overton. 



The House Fly a Pest. — The house fly is recognized the world 

 over as a pest. Not only do flies spoil much food by means of 

 their filthy habits, but the far more important charge of spreading 

 disease is now laid to them. The bacteria causing typhoid fever 

 might be carried on their feet; so flies could easily carry the 

 typhoid bacteria to a dish of milk, thus infecting the milk and 

 causing danger to all drinking it. 



Development. — The development of the house fly is very rapid. 



hunter's BIOL. — 16^ 



