Complex sentence: The practice of raising silkworms by children as pets has, in the nonsilkfarming country of South Africa, led to the development of extremely hardy landraces of silkworms, because they are invariably subjected to hardships not encountered by commercially farmed members of the species.
Split into simpler sentences: The practice of raising silkworms by children as pets has, in the non-silkfarming country of South Africa, led to the development of extremely hardy landraces of silkworm. This is because they are invariably subjected to hardships not encountered by commercially-farmed members of the species.