Venus fly-trap, an insectivorous plant, normally grows in swamps and moist soils characterized by lack of sufficient nitrogen (as nitrates). Their root system is also not so well developed. As a result these plants tend to trap insects and ‘digest’ them to augment their nitrogen supply. These carnivorous plants do not have any special mechanisms or honey secretions to attract insects but only modified leaf traps (Dionaea muscipula), vase-like leaves (Nepenthes Khasiana), leaf hairs having glue on their tips (Drosera) and leaf surface having a sticky coating (Pinguicola alpina) to trap them. In Venus fly-trap plant, the two halves of the leaf blades can swing upward and inward as though hinged.
Inside the hinged portion of each leaf are several long trigger hairs. As the insect walks along the leaf surface and touches these hairs, it stimulates a hydraulic response in the leaf-cells and makes them lose water rapidly. This causes the leaves to close. Long projections along the leaf margins help in trapping the insect.
Once an insect is trapped, digestive enzymes are secreted by the hairs which ingest the insect and absorb the contents. After a meal, the trap opens again only after several days. Generally each modified leaf is used to trap only 3-4 insects before it falls.
These plants also have chlorophyll by which they can photosynthesis to cater to their energy (food) requirements. Hence these plants are not obligatory carnivorous forms. But they can grow exuberantly to produce flowers and seeds, if insects are available, as they supplement their nitrogen supply.