There is an intimate relationship between insects and plants. Neither could exist without the other. Bees, wasps, and butterflies benefit plants by pollinating their flowers. Other insect species feed on plants by sucking sap from plant tissue or by devouring plant parts. However, in a fascinating twist of nature, there are a small number of plants that "eat" insects. The diet of these plants also includes mites, sowbugs, and occasionally small animals, such as frogs. Accordingly, these flesh-eating plants are true carnivores.
Carnivorous plants don't survive solely by "eating" insects and other prey. Carnivorous plants, as all green plants, contain chlorophyll and manufacture food via photosynthesis. Insects and other small creatures are simply a supplemental food source for carnivorous plants.
The Venus' fly trap, pitcher plant, and sundew are carnivorous plants that make fascinating houseplants.
Venus' Fly Trap
The Venus' fly trap (Dionaea muscipula) is native to a small coastal area in North and South Carolina. The plant consists of a rosette of flattened leaves. The upper portion of each leaf has a trap-like structure. The two-lobbed trap is hinged down the center and fringed with long, teeth-like projections. The inner surface of the trap is dark pink to red. There are also 3 trigger hairs on the inner surface of each lobe. Nothing happens if only one trigger hair is touched by an insect. However, when one trigger hair is touched twice or when two are touched in succession, the trap closes. The teeth-like projections interlock, trapping the unsuspecting victim inside. The struggling victim stimulates the secretion of digestive juices. These juices digest the soft parts of the insect. Only the hard, indigestible parts of the insect remain when the trap reopens in about 10 days. The open trap then awaits its next victim.
There are several genera (groups of plants with common traits) which are referred to as pitcher plants. The genera Sarracenia and Darlingtonia are native to North America. Plants in the South American genus Heliamphora, the tropical Asian genus Nepenthes, and the Australian genus Cephalotus are also called pitcher plants.
All pitcher plants have modified leaves or leave parts that resemble a pitcher. The pitcher- like structure holds water and is topped with a hood or lid. Unsuspecting insects and other prey wander into the pitcher. Escape from the pitcher is prevented by a smooth surface, downward- pointing hairs, or inrolled rim. Eventually the trapped victim falls into the water and drowns. The drowned victim is then converted to plant nutrients by digestive enzymes in the water.
There are more than 100 species of sundews (Drosera). Sundews are mostly short- stemmed plants consisting of a rosette of foliage. Depending on the species, the leaves vary from thread-like to paddle-shaped to nearly round. The leaves are covered with tiny (usually red) hairs. These hairs exude a clear, sticky fluid. (The dew-like secretions give the plants their common name.) The sticky droplets trap unwary insects or other small creatures that come in contact with it. The struggling victim stimulates the hairs to bend inward, drawing it closer to the leaf where it is digested into plant nutrients.
Carnivorous plants have more exacting requirements than most commonly grown houseplants. Carnivorous plants require a moist, acidic growing medium, high relative humidity, and bright light.
Excellent containers for carnivorous plants include a fish aquarium or large terrarium. A piece of plexiglass placed over the top will help maintain a high relative humidity. Ventilation can be provided by keeping the plexiglass slightly ajar.
A suitable growing medium for carnivorous plants consists of 2 parts sphagnum peat moss and one part coarse sand. If using a fish aquarium or terrarium, place 1 inch of coarse gravel on the bottom before adding the growing medium.
Good lighting is essential for carnivorous plants. An east or west facing window that receives at least 1 or 2 hours of direct sun is fine. A fluorescent light fixture containing two 40 watt tubes can be used in poorly lit areas.
Day-time temperatures should be 70 to 75 F during the summer and 55 to 60 F in winter.
When watering carnivorous plants, use rain or distilled water. Tap water may be too alkaline or contain too many minerals.
Finally, there is usually no need to fertilize carnivorous plants. These plants are native to areas with low nutrient levels. If you do fertilize, a 1/4 strength solution of fish emulsion every 2 to 4 weeks during the growing season should be sufficient. Do not feed them hamburger.
Carnivorous plants are a fascinating group of plants. Their amazing growth characteristics and ability to eat insects and other small creatures are simply adaptations to their unique environment.
This article originally appeared in the December 11, 1998 issue, pp. 132-133.