A snail with its eyes infected with green-banded broodsac flatworm. A type of flatworm called the green-banded broodsac infects snails’ eyes, making the eyes look like caterpillars. This attracts birds that prey on caterpillars. Once a bird eats the snail, the green-banded broodsac matures and releases its eggs, which exit the bird’s body through its droppings.

What kind of relationship do snails and green-banded broodsacs share?