=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 the moulting 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 caterpillar 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 stages: (1) _egg_, (2) _larva_, (3) _pupa_, and (4) _imago_, or perfect insect (Figs. 136, 137, 138). [Illustration: FIG. 136.—Measuring worm, the larva of a moth. ] [Illustration: FIG. 137.—Pupa of a mosquito. ] The egg stage is one of development, no nourishment being absorbed. The larval stage is one of voracious feeding and rapid growth. In the pupa stage no food is taken and there is no growth in size, but rapid development takes place. In the perfect stage food is eaten, but no growth in size takes place. In this stage the eggs are produced. When there is very little resemblance between the larva and the imago, and no pupal stage, the metamorphosis, or change, is said to be _complete_. When, as with the grasshopper, no very marked change takes place between the larva and the imago, there being no pupal stage, the metamorphosis is said to be incomplete. By studying the illustrations and specimens, and by thinking of your past observations of insects, determine which of the insects in the following list have a complete metamorphosis: beetle, house fly, grasshopper, butterfly, cricket, wasp. [Illustration: FIG. 138.—THE FOUR STAGES OF A BOTFLY, all enlarged. _a_, egg on hair of horse (bitten off and swallowed); _b_, larva; _c_, larva with hooks for holding to lining of stomach; _d_, pupal stage, passed in the earth; _e_, adult horse fly. ] RECOGNITION-CHARACTERS FOR THE PRINCIPAL ORDERS OF ADULT WINGED INSECTS