FIELD BOOK OF INSECTS. 



get back to their food. Another device is shown, in 

 section, in Plate IV. It is made of plaster of paris. The 

 water at b keeps the block moist. It is useful chiefly 

 for ground-inhabiting larvae or for galls. However, for 

 the latter, fruit jars with moist sand or a moist sponge in 

 the bottom do just as well or better. Do not forget the 

 Iarva3 living in hollow stems, dead wood and under bark. 

 When caterpillars are about to molt, especially when 

 they are about to change to pupae, they stop eating and 

 act as though they are sick. If you are in doubt as to 

 how the species pupates, it is well to give it potting soil 

 covered with dead leaves and some twigs of their food- 

 plant, not merely fresh leaves. A desirable, but not 

 necessary, refinement of technique is to bake the soil in 

 order to kill bacteria and fungi. Species which "should" 

 pupate underground will get along fairly well even if they 

 have no earth much better than if they be covered with 

 earth after pupation takes place, as this would pack them 

 and that is injurious. 



KILLING 



Up to this point but little mention has been made of 

 killing insects and that was really not necessary. Insects 

 can be studied alive with great pleasure and profit. How- 

 ever, there are so many kinds and the differences between 

 species are often so minute that it is well to kill and 

 preserve at least samples. Fortunately, this can be done 

 with less trouble and less injury to the balance of Nature 

 than is the case with most animals or even plants. Further- 

 more, the collection can be made very attractive and 

 instructive without taking up much space. 



The best all-around killing agent for adult insects is 

 cyanide of potassium. It should be broken into pieces 

 varying in size from that of a small pea to that of a hickory 

 nut, according to the size of the bottle to be used. Olive 

 bottles make good medium-sized bottles, while fruit jars 

 are better for large-sized moths and butterflies. Tubes, 

 even as small as ^4 in. in diameter by about 2 in. long, 

 are not too small for some things. Avoid bottles with 

 strongly constricted necks. Avoid, also, bottles made of 



16 



