156 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



chiefly on sweet or starchy materials,, sometimes doing real 

 damage in libraries, where it attacks the book bindings. It 

 attacks starched clothing, eats the paste off the wall-paper, 

 causing it to loosen, and infests dry starchy foods. It runs 

 swiftly and avoids the light. It can be killed by spreading 



pyrethrum powder in book cases, 

 wardrobes and pantries. Another 

 species, called the bake-house sil- 

 ver fish, Lepisma domestica, is often 

 common about fire places and 

 ovens, running over the hot metal 

 and bricks with surprising immu- 

 nity from the effects of the heat. 



All of the Aptera when hatched 

 from the egg very much resemble, 

 except in the matter of size, the 

 parent form. And they reach the 

 adult condition with very little 

 change except that of a marked 

 growth in size. 



Order Ephemerida. The Ephe- 

 merida or May-flies, or lake-flies, 

 are a small order of delicate four- 

 winged insects which live in adult 

 condition for from but a few hours 

 to a few days, varying with different 

 species. They have soft, poorly 

 developed mouth-parts of biting 

 type, or no mouth-parts at all, and 

 probably only a few kinds take any 



food as adults. The wings are very thin and many veined, 

 with the hind wings smaller than the fore wings, or even 

 wholly lost in a few species. 



The eggs are dropped into the water of ponds or quiet stream 

 pools, and the young which hatch from them are soft-bodied 

 flat creatures, called nymphs, which crawl about on the bottom, 

 often on the undersides of stones. They have well-developed 

 biting mouth-parts with sharp-pointed mandibles. They 



FIG. 69. Young (nymph) 

 of May-fly, showing (g) tra- 

 cheal gills. (Three times 

 natural size; after Jenkins 

 and Kellogg.) 



