THE HOUSE-FLY 



373 



Flies come to ships newly arrived in port 

 across considerable stretches of water. 

 This we know, because a few hours ear- 

 lier there- were no flies on the ship. No 

 communication has been had with land. 

 The flies must have come on their own 

 wings. Occasionally we see a fly follow 

 a team or animal, easily keeping' up a 

 good pace. The wing muscles of a fly 

 when weighed are found heavier in pro- 

 portion than those of any bird so far ex- 

 amined. It is difficult to tire a fly out. 

 Test this by trying ^o keep one constantly 

 on the wing in a room and you will soon 

 find you have no easy task. All this 

 shows the fly to be no mean navigator 

 of the air. 



If such an active and adventurous in- 

 sect as the fly carries disease germs it 

 will quickly spread them far and wide. 



Most of our diseases are caused by in- 

 visible germs that lodge and grow in our 

 bodies, destroying our tissues or poison- 

 ing us with their excreta. These germs 

 may be brought to us from some sick per- 

 son by whatever is large enough to carry . 

 them and has the opportunity. Combine 

 this fact with what every one knows 

 about flies, and we see at once the tre- 

 mendous importance of flies as carriers 

 of human disease germs. 



The result of tiiis simple piece of rea- 

 soning is so startling that it is often side- 

 tracked by its own importance. It looks 

 so incredible that we hesitate, distrust- 

 ing our own logic. It seems incredible 

 that men have gone on doing as they 

 have done, and as they are still doing, if 

 the facts are as they seem. The conse- 

 quences of our reasoning seem so tre- 

 mendous we fear there must have been 

 a mistake somewhere. And so we dis- 

 miss the idea. 



One way to disturb this false security 

 is to interest people in the habits and 

 structure of flies. The more we know 

 about flies the more clear it will become 

 that thev are among our worst enemies. 



The photographs illustrating this arti- 

 cle have been designed with this end in 

 view. Take for instance the view of the 

 flv resting on glass and viewed from be- 

 low. Look at the feet, and observe that 



each of them has two claws and two 

 light-colored pads. The fly clings to 

 rough surfaces by means of the claws, 

 and to smooth surfaces by a combined 

 action of the claws and pads. The fly's 

 pads are covered with thousands of 

 minute short hairs, sticky at the end. 

 There is no suction — merely adhesion. 



The action of a fly's pads may be illus- 

 trated by means of a piece of sticking 

 plaster and a few threads and small 

 weights. Take a piece of sticking plaster 

 half an inch wide and sew through it 

 some short pieces of thread at intervals 

 of half an inch, and knot the threads on 

 the sticky side so that they cannot pull 

 through. Stick the plaster to a dinner 

 plate or other smooth object and it will 

 be found that if a small weight is at- 

 tached to each thread the plaster will 

 sustain in this way a considerable 

 weight — that is to say, the sum of all the 

 small weights is considerable. 



Now, remove the weights and attach 

 all of them to one or two of the threads 

 at one end. The plaster will promptlv 

 be torn loose. Acting on a portion of 

 the plaster at a time, the weights can ac- 

 complish what they cannot accomplish 

 when distributed along the whole sur- 

 face of the plaster. 



This experiment illustrates roughl\ 

 how the fly uses and controls its feet. Oi 

 course, in my illustration you can see 

 just how the weights release the plastei 

 from end to end. It is very difficult to 

 make this observation on a fly. because 

 the fly's pad is so small, and more par- 

 ticularly because the whole operation 

 takes place in something like the fiftieth 

 part of a second. 



Wonderful as the fly's pads are. they 

 have their disadvantages, for stickiness 

 and locomotion are not always strictly 

 compatible. Humorous use is made of 

 this idea in Uncle Remus tales, "The Tar 

 Baby" and "The Outrageous Prank of 

 Brer Rabbit." In one of these Brer 

 Rabbit takes advantage of the stickiness, 

 not only of his feet, but the rest of his 

 anatomy, to strike terror into the souls 

 of the other animals. Raiding Brer 

 Bar's pantry, he accidentally breaks the 



