Linked from
The 16 pages that link to Ovipositor, each with the reason it gives.
Fig waspRelated: Female fig wasps use it to lay eggs in fig flowers.
Parasitoid waspRelated: Female parasitoid wasps use it to place eggs on or inside hosts.
CalliphoridaeRelated: Female blow flies use it to place eggs on suitable breeding material.
CurculionidaeRelated: Some weevils use it to insert eggs into seeds or plant tissues.
SnakeflyRelated: Female snakeflies use a long ovipositor to lay eggs in crevices or bark.