Plantwatch: the plants that kill their insect pollinators

Jack-in-the-pulpit plants lure in gnats, cover them in pollen and trap them. As they struggle to escape they pollenate female flowers

There are two plant species with the most brutal flowers in the world, which deliberately kill their insect pollinators. The flowers of jack-in the pulpit, Arisaema angustatum, and its close relative Arisaema peninsulae are hidden inside a bowl-shaped wrapper with a narrow entrance, with a tall hood standing above. The floral dungeon lures in male fungus gnats, possibly by imitating the sexy scent of female gnats to fool the males into finding a mate.

When the plants are small they only develop male flowers, which cover the gnats in pollen. The floral prison is too slippery for the gnats to climb out of, and their only escape is through a tiny hole in the chamber, before they can fly off and fall for the same trick on another plant. But as the plants grow larger, they develop female flowers and the escape hole closes and so gnats falling into the floral prison now become well and truly imprisoned. As they desperately try to escape they smother the female flowers with pollen, but with no escape route and no food, the gnats eventually die – quite possibly the cruellest cross-pollination strategy of any known flower.