(1687) Flies , and almost all moving creatures , that cannot feed their own young , have the tendency , from an innate instinct , to lay their eggs in such places where their young , on coming out of their Eggs , will find nourishment .Now when these Flies and also other species , do not come across any Flesh , Fish , or some animal ' s guts , they may as well lay their Eggs where they can smell that there will be some food forParasite - flies in pupae of butterflies .their young , and that may also be on the Pupea which came forth from the Caterpillars .