Forgotten Planet, The by Murray Leinster (1896 - 1975)

The "forgotten" planet had been seeded for life, first with microbes and later with plants and insects. A third expedition, intended to complete the seeding with animals, never occurred. Over the millennia the insects and plants grew to gigantic sizes. The action of the novel describes the fight for survival by descendants of a crashed spaceship as they battle wolf-sized ants, flies the size of chickens, and gigantic flying wasps. (Summary by Wikipedia)