80 ANIMAL BIOLOGY 



stinct. Moths, for example, are used to finding nectar in 

 the night-blooming flowers, most of which are white. The 

 habit of going to white flowers is transmitted in the struc- 

 ture of the nervous system ; so we say that moths have 

 an instinct to go to white objects ; it is sometimes more 

 obscurely expressed by saying they are attracted or drawn 

 thereby. 



Instincts are not Infallible. They are trustworthy in 

 only one narrow set of conditions. Now that man makes 

 many fires and lights at night, the instinct just mentioned 

 often causes the death of the moth. The instinct to 

 provide for offspring is necessary to the perpetuation of 

 all but the simplest animals. The dirt dauber, or mud 

 wasp, because of inherited habit, or instinct, makes the 

 cell of the right size, lays the egg, and provides food for 

 offspring that the mother will never see. It seals stung 

 and semiparalyzed spiders in the cell with the egg. If 

 you try the experiment of removing the food before the 

 cell is closed, the insect will bring more spiders ; if they 

 are removed again, a third supply will be brought; but if 

 taken out the third time, the mud wasp will usually close 

 the cell without food, and when the egg hatches the grub 

 will starve. 



The Development of Insects. The growth and molting 

 of the grasshopper from egg to adult has been studied. 

 All insects do not develop exactly by this plan. Some 

 hatch from the egg in a condition markedly different from 

 the adult. The butterfly's egg produces a wormlike cater- 

 pillar which has no resemblance to the butterfly. After 

 it grows it forms an inclosing case in which it spends a 

 quiet period of development and comes out a butterfly. 

 This change from caterpillar to butterfly is called the 

 metamorphosis. The life of an insect is divided into four 



