There are about 70 species of butterworts worldwide. Many are found in Mexico and in Europe. They grow on wet, dripping, moss-covered rocks in the mountains, on moist, grass-covered sandy ditches in savannas, and in other similar conditions, sometimes in company of other carnivorous plants. Of six species found in the southeastern United States, five are indigenous to the region. Three other species grow in northern U.S. and Alaska.

Butterworts are a rosette of thin leaves, typically lying prostrate, with white, fibrous roots. The upper surface of the leaf is covered with short stalked glands that secrete clear, sticky mucilage to trap small animal prey. The leaf feels greasy to the touch because of this secretions. This gave the plant its common name. The genus name Pinguicula is derived from the Latin word pinguis, meaning fat.

Many butterwort rosettes have close resemblance to each other, and it is often difficult to distinguish one species from another when the plants are out of flower. The leaf is yellowish-green in most species but has a distinctive reddish color in some species (including one U.S. species). The diameter of the rosette varies anywhere from 2  to 15 cm depending on the species.

Most of the prey the butterworts are capable of trapping is small insects such as gnats, mosquitoes and small ants. When an insect lands or crawls on the upper surface of the butterwort's leaf, the insect is mired down to the surface by the sticky substance secreted by the stalked glands, as in sundews. Unlike sundew tentacles, however, these short stalked glands offer no movement. The stalked gland consists of 16 radiating glandular cells supported on a single-celled stalk.

Scattered over much of the leaf surface are another kind of glands with a similar structure. These are sessile (stalkless) glands consisting of 8 radiating glandular cells. These sessile glands are responsible for the secretions of digestive fluids and the subsequent absorption of the products of digestion. Studies have shown that nitrogenous compounds placed on the leaf surface precipitate the enzyme secretions from sessile glands in a matter of minutes.

When a small insect -- or any nitrogenous substance such as a piece of meat -- is placed on the leaf surface, there is copious secretions of digestive fluid from the sessile glands. Often a trapped insect sinks down to the leaf surface -- completely submerged in the digestive fluids -- and comes into direct and tight contact with sessile glands on the leaf surface. The secretions are also shown to contain an antiseptic substance which effectively prevents bacterial activities during the course of the digestive process if the prey is small enough which, in nature, is usually the case.

The resultant digested material is absorbed through the sessile glands. Studies using radioactive isotope (carbon 14) show that products of digestion are rapidly taken into the leaf in a matter of a few hours and are carried to the other parts of the plants.

Often the leaf movement is observed in association with the capture of prey. When a small prey is placed on the leaf surface near the leaf margin, the leaf begins to curl up. It is a slow motion taking several hours and possibly lasting several days. Also, the amount of curling is rather limited. It is unlikely, therefore, that the leaf movement contributes to the entrapment of the prey in the same degree as observed in the leaf-folding in some sundew species. It is also noted that the contact of an insect with the leaf (away from the margin) results in the dishing of the leaf area below the prey.

All leaf movements are known to be caused by the stimulation to the leaf surface and are attributed to a growth phenomenon. Although not as active as tentacle bending or leaf folding in sundews, the leaf movement in butterworts is a matter of common observation. How much significance should be given to it is debatable. A general interpretation is that the upwardly curled leaf margin -- and localized dishing effect of the leaf by stimulation -- help to hold the secretions in place during the digestion process.

Butterworts produce a showy display of colorful flowers which are borne singly (for most species) at the tip of a slender, often glandular, pubescent scape. Early spring is the flowering season for most U.S. species. The zygomorphic (laterally symmetric) flower has a sympetalous (united petals) corolla forming a cylindrical tube which divides into five lobes (2 lobes on the upper lip & 3 on the lower lip) on the front and terminates in a slender spur on the back. The spur is a nectar container, a structure commonly seen in insect-pollinating flowers. Near the lower entrance of the corolla tube projects a hairy structure known as a palate. The microscopic structure of the palate hairs, along with the color and shape of the entire corolla, is characteristic to each species and can be used for the identification. On the upper side of the inner corolla tube are located two stamens and a stigma lobe. A wide stigma lobe covers anthers for incoming pollinators, thus providing a mechanism to discourage self-pollination.

After the flower, the scape grows further as it straightens itself. The seeds mature in a month or so. The seed capsule contains hundreds of tiny, powder-like seeds. Seeds have a distinctive surface pattern for each species.

Apart from the carnivorous nature of the butterwort plants, people in Scandinavian countries have mixed the leaf extracts with fresh milk to make it curdle.