Trap Types
Carnivorous plants have evolved incredible adaptations to allow them to catch and retain prey. Some have ‘active’ traps which use movement to secure their victims, others are ‘passive’ and capture food without moving.
Five main trapping methods are currently known:
Snap Traps
Probably the most famous, the toothed snap traps of the Venus Flytrap (Dionaea muscipula) are also among the most advanced in the carnivorous plant world. Sensitive hairs in the mouth of the trap detect the movements of potential prey, and trigger the trap to snap closed in a fraction of a second.
This trapping mechanism is shared by Dionaea‘s close relative the Waterwheel Plant (Aldrovanda vesiculosa), a fully aquatic species with whorls of underwater snap traps.
Sticky Traps
Many carnivorous plants rely on sticky mucilage to capture unwary prey. Insects and other small creatures that touch this shiny glue quickly become stuck.
Sundews (Drosera) secrete their mucilage from the ends of tentacle-like hairs. Many species can move their tentacles, or even curl their leaves around prey to prevent its escape. Butterworts (Pinguicula) can also roll their leaf edges.
Other carnivores such as Byblis and Drosophyllum use passive sticky traps.
Pitfall Traps
Apparently simple but remarkably effective, pitfall traps catch prey by simply waiting for it to fall in, and making it hard to climb back out. The traps, known as ‘pitchers’, usually contain liquid in which the prey drowns and is digested.
This trapping method has evolved separately in carnivorous plants on several different continents – Sarracenia and Darlingtonia in North America and Heliamphora in South America; Nepenthes in tropical South-East Asia and Cephalotus in Australia.
Pitfall traps were traditionally considered passive, but recent research indicates that some Nepenthes tropical pitcher plants use falling raindrops to springboard prey into the trap!
Bladder Traps
The fastest-moving traps of any carnivorous plant belong to the Bladderworts (Utricularia). Their tiny bladder traps grow in water or underground in wet soils.
The plant pumps water out of the bladder traps, creating a vacuum inside. When prey touches mechanical trigger hairs near the mouth of the trap, a trapdoor flips open. The victim is sucked inside the bladder and the trapdoor snaps shut. The entire process can be completed in only 10-15 milliseconds.
Lobster Pot Traps
In lobster pot traps (sometimes also known as ‘eel traps’, prey enter via a small opening and find it difficult to navigate back out, or are prevented from escaping by angled bristles.
Like their relatives the Bladderworts, the Corkscrew Plants Genlisea spp. have underground or sub-aquatic traps. In Genlisea the traps consist of a forked tube; the branches of the fork have a spiral slit along their length. Prey that enters a branch through the slit cannot leave due to angled hairs but can only progress further up into the tube.
The traps of the Parrot Pitcher plant Sarracenia psittacina and the Cobra Lily Darlingtonia californica also use the lobster-pot principle.