Cape Sundew (Drosera capensis) with fly

The image shows a fly trapped by glandular hairs on a leaf of Cape Sundew. The fly is approximately 1 cm long.

The image shows a fly trapped by glandular hairs on a leaf of Cape Sundew. The fly is approximately 1 cm long.

These delicate-seeming plants are highly adapted for life in the unforgiving peat bogs, capturing and preying upon insects to make up for the lack of nutrients in the soil.

A sticky-trapped carnivorous plant with long spatula-shaped leaves originally from South Africa. These plants have adapted to soils with high moisture and low nitrogen levels by attracting, capturing and digesting insects.

Sundews have sticky traps, with ‘tentacles’ (trichomes) with glandular heads. These heads contain glandular cells that produce a sticky mucilage. The mucilage is an acidic (pH 5) polysaccharide solution, which also contains calcium, magnesium, potassium and sodium ions.

Prey, mainly winged insects, are attracted to the reflection of light in the ‘dewdrops’ of mucilage, and to the conspicuous reddish ‘tentacles’.

Once on the leaf, the prey animals get stuck to the mucilage drops. As they struggle to escape, they become even more covered in the mucilage. The struggle stimulates the tentacles around the victim to bend inwards, causing the leaf to curl, and trapping the insect further. The prey animal is eventually so covered in mucilage that it suffocates.

This is not just a passive process. The struggle by the victim is actually detected by the plant. Action potentials are generated that move from the tentacles to the leaf surface. This causes curling in the stimulated tentacle. The tentacle movement lasts up to 30 minutes. In addition, chemical stimuli in other tentacles can also occur, causing more leaves to curl, and completely enveloping the prey animal.

Digestive enzymes are released from glands into the mucilage surrounding the prey animal, and the soft parts are digested very quickly. Indeed, Darwin found that Drosera rotunidfolia was able to break down a 1.25cm cube of egg white completely after 50 hours. The nutrients are reabsorbed by the plant’s tentacle knobs and the sessile glands.