insectivorous plants

perennial herbaceous plants that trap insects (or, rarely, other small animals) and use them as a supplementary source of nourishment, primarily for nitrogen.

Insectivorous plants are found throughout the world. There are 500 species distributed in six different families, including Droseraceae, Lentibulariaceae, Nepenthaceae, Sarraceniaceae, and Cephalotaceae. In the USSR there are approximately 18 species, representing four genera distributed in the families Droseraceae (Drosera and Aldrovanda) and Lentibulariaceae (Utricularia and Pinguicula). Insectivorous plants grow in fresh-waters, marshy ponds, and swamps—that is, on soils with low nitrogen content. Nitrogen starvation is unavoidable in such circumstances, as are deficiencies in phosphorus, potash, and other substances.

The plants obtain supplementary minerals from insects, which they capture by means of specially modified leaves. The surfaces of such leaves have glands, which excrete digestive enzymes of the pepsin type and such organic acids as formic acid and benzoic acid. The enzymes break down the proteins in the bodies into simpler compounds, which are readily assimilated by the plants.

The root systems of terrestrial insectivorous plants are poorly developed; those of aquatic species have atrophied. Nevertheless, the plants are able to survive on substances obtained from the soil or the water. Supplementary nourishment from animal substances accelerates plant development and the transition to flowering and fruiting.

Some insectivorous species (sundews, butterworts, Drosophyllum) have leaves covered with numerous capitate glandular hairs that excrete a sticky transparent liquid to attract and snare insects. When an insect is caught, the plant’s gland secretion increases; the glandular hairs bend toward the insect (in sundews) or the edges of the entrapping leaf fold around the insect (butterworts). Other insectivorous plants have pitfall traps (Nepenthes, Sarracenia, Darlingtonia) or mechanical traps (Dionaea, Aldrovanda, Utricularia).