Insect Study 



409 



Supposing the fly which wintered behind the window curtain in your home 

 last winter, flew out to the stables about May ist and laid 120 eggs in the 

 sweepings from the horse stable, all of which hatched and matured. 

 Supposing one-half of these were mother flies and each of them, in turn, 

 laid 120 eggs, and so on for five generations, all eggs laid developing into 

 flies, and one-half of the flies of each generation being mother flies. How 

 many flies would the fly that wintered behind your curtain have pro- 

 duced by September? 



12. Pour some gelatin unsweetened, on a clean plate. Let a house- 

 fly walk around on the gelatin as soon as it is cool ; cover the plate to keep 

 put the dust and leave it for two or three days. Examine it then and see 

 if you can tell where the fly walked. What did it leave in its tracks? 



13 . Write an essay on the house-fly, its dangers and how to combat it, 

 basing the essay on Bulletins of the U. S. Department of Agriculture. 



THE COLORADO POTATO-BEETLE 



Teacher's Story 



HE potato-beetle is not a very attractive insect, 

 but it has many interesting peculiarities. No 

 other common insect so clearly illustrates the 

 advantage of warning colors. If we take a 

 beetle in the hand, it at first promptly falls 

 upon its back, folds its legs, and antennse down 

 close to its body, and "plays possum" in a very 

 canny manner. But if we squeeze it a little, 

 immediately an orange-red liquid is ejected on 

 the hand, and a very ill-smelling liquid it is. 

 If we press lightly, only a little of the secretion 

 is thrown off; but if we squeeze harder it 

 flows copiously. Thus a bird trying to swallow one of these beetles, would 

 surely get a large dose. The liquid is very distasteful to birds, and it is 

 indeed a stupid bird that does not soon learn to let severely alone orange 

 and yellow beetles, striped with black. The source of this offensive and 

 defensive juice is at first a mystery, but if we observe closely we can see it 

 issuing along the hind edge of the thorax and the front portion of the 

 wing-covers ; the glands in these situations secrete the protective juice as 

 it is needed. The larvse are also equipped with similar glands and, there- 

 fore, have the brazen habit of eating the leaves of our precious potatoes 

 without attempting to hide. They seem to know that they are far safer 

 when seen by birds than when concealed from them. 



The life history of the potato-beetle is briefly as follows: Some 

 of the adult beetles or pupae winter beneath the surface of the soil, 

 burrowing down a foot or more to escape freezing. As soon as the potato 

 plants appear above ground the mother beetle comes out and lays her eggs 

 upon the under sides of the leaves. These orange-yellow eggs are 

 usually laid in clusters. In about a week there hatches from the eggs 

 little yellow or orange humpbacked larvae, which begin at once to feed 

 upon the leaves. These larvse grow as do other insects, by shedding 



