Complex sentence: Insects are mostly soft bodied, fragile and almost defenseless compared to other, larger lifeforms, while the immature stages are small, move slowly or are immobile, hence all stages are exposed to predation and parasitism.
Split into simpler sentences: Insects are mostly soft bodied, fragile and almost defenseless compared to other, larger lifeforms. The immature stages are small, move slowly or are immobile, and so all stages are exposed to predation and parasitism.