Speaking generally, the time taken up in hatching the eggs of insects is very variable. It is a general rule that the eggs which are laid in the autumn must abide the return of spring before they will be hatched. But when eggs are deposited in the summer, they are often hatched in a very short time. The eggs of the painted-lady butterfly are hatched in about eight days, those of the lady-bird in a little less, from five to six days; the eggs of another species of butterfly occupy a month, those of spiders three weeks, those of bees only three days, and those of the meat-fly shorter than any--only a few hours; it has even been stated that in very warm weather the eggs of the meat-fly will be hatched in about two hours! In most of these cases much depends upon the weather; but even this does not operate beyond certain limits, for it has been said that in the month of June, even if silk-worm's eggs were placed in an ice-house, they would be hatched in spite of the cold, but this observation deserves to be repeated.
It would be impossible to make the exact nature of the changes which take place in the egg from first to last easily understood in a work of this kind. They have occupied the laborious investigation of talented observers with the highest powers of the microscope, and although much is now known on the subject, it is of a nature too abstruse to be dwelt upon in our unpretending volume. As we may well imagine, the changes are wonderful indeed which from a little drop of fluid matter, contained perhaps in a shell not larger than a pin's head, end in the development of the living and active larva, who makes his speedy escape out of his shell-cradle. But they must be studied in the scientific treatises which are written upon this subject, and they are so interesting as amply to repay the task of investigation. It may be added, however, as a curious fact, that contrary to the general rule in the egg of birds, some of the eggs of insects actually grow larger before they are hatched, and frequently the shape alters also.