THE AMAZING INSECT-EATING PLANT

by Randi Lynn Mrvos

The Venus flytrap is probably the best know insect-eating plant, but it is only one variety out of nearly 600 species of carnivorous plants. To be called carnivorous, plants must digest and use nutrients from insects or animals in order to help them survive, grow, and make pollen and seeds. They have the ability to actively attract, capture, and eat their prey. Botanists believe that carnivorous plants evolved about 125 million years ago, after the appearance of insects and flowering plants. These plants probably mutated from non-carnivorous plants as they adapted to nutrient-poor environments, such as limestone cliffs or acidic bogs.

One of the most fascinating carnivorous plants is the pitcher plant, which is a member of the group of plants called Sarracenia. Pitcher plants can be divided into two distinct groups based on their height. Prostrate pitchers lie along the ground horizontally, and upright pitchers grow vertically up to 3 feet tall. Sarracenia can be found in northern and southwest Australia, Venezuela, Madagascar, and Southeast Asia. They also grow from the gulf coastal plain of the United States, up to the east coast to Maine, and into the Great Lakes region, as well as eastern and southern parts of Canada. Most Sarracenia are trumpet-shaped, and they have an opening partially covered by a thin leaf. Some are squatty or have unusually shaped pitchers. For example, Sarracenia purpurea, the purple pitcher, has a lid that points upward to collect rain water, and Sarracenia psittacina, the semi-aquatic parrot pitcher, has a reclined pitcher with a beak-like structure.

Sarracenia lure insects foraging for food. They catch ants, moths, flies, butterflies, and beetles. There are some Sarracenia, such as Nepenthes, the tropical pitcher plant, that trap rats, frogs and birds. These cases are rare, and the animals captured are probably already sick or near death. Usually Nepenthes fills its diet with crawling insects. Pitcher plants are passive carnivores, unable to move to catch their prey. Each species, however, uses a different, amazing trick to trap insects. Some varieties have colorful flowers or sweet fragrances to lure prey. For example, Sarracenia flava has an intoxicating nectar that makes insects so drowsy that they fall into the pitcher. After the insect is lured, some species, such as Sarracenia minor and Sarracenia psittacina, fool their prey with a false exit. When the insect tries to leave through window-like openings, it becomes trapped. Once inside the pitcher, insects slip on a waxy substance, and they fall further into the narrow structure of the plant, unable to move. Downward-pointing hairs inside the pitcher push the prey deeper where digestion begins. Many carnivorous plants depend on bacteria to supply the digestive enzymes, so that they can absorb the decayed insect. However, Sarracenia, combine their own digestive fluids with bacterial enzymes. This is an example of symbiosis, a mutual cooperation which benefits both the bacteria and plants.

Pitcher plants are not like typical garden perennials, but they share some similarities. Both kinds of plants have flowers that attract insects, and they absorb nutrients through roots and leaves. Like other plants, Sarracenia also engage in photosynthesis, a process that plants use to change light energy from the sun into food. Some non-carnivorous plants act like carnivorous plants. Orchids trap insects temporarily to ensure pollen transfer, and petunias catch and kill insects for defensive purposes. Other plants, such as Roridula, a plant found in South Africa, kill insects with a sticky resin, but do not digest the prey. The prey is digested by assassin bugs that are capable of living on the plant. In return, they secrete nutrients on the leaves, which are absorbed by the plant. Bugs and plant have a symbiotic relationship.

Growing pitcher plants can be fun. They can be planted in a garden if the soil is acidic, and the climate is hot and muggy. Most gardeners, however, rely on a terrarium or greenhouse. Pitcher plants are picky about soil, and thus commercial potting soils are not recommended. Use a nutrient-poor soil of peat moss and sand (3 parts peat moss to 1 part silica or perlite-available in most garden centers). Sarracenia should be planted in a plastic container or glazed ceramic pot with drainage holes on the bottom. Place the pots on a bed of sand, or in shallow ponds or wading pools. They need plenty of purified or distilled water, except in late fall when the plants go dormant and die back to the surface. At this time place pitcher plants in a well-ventilated area to prevent mold growth. Sarracenia need at least 4 hours of light each day. Place the plant in a south or west-facing windowsill and use curtains or shades to prevent burning. During the growing season, twin-tube fluorescent lighting or grow-light tubes can be used for 14-15 hours/day, if there is insufficient light. The erect trumpet species is an exception, however. Since they require a tremendous amount of sunshine, they are not suited to growing inside.

Sarracenia are exciting to grow and fun to watch. Although it may take five to seven years before plants reach maturity and bloom, most gardeners will agree that Sarracenia are worth the wait!

REFERENCE

1. Camillerri, Tony, Carnivorous Plants, NSW, Australia: Kangaroo Press, 1998
2. D'amato, Peter, The Savage Garden, Berkeley, CA: Ten Speed Press, 1998

WEB SITES

Meyers-Rice, Barry, "The Carnivorous Plant FAQ", 2001

Zenner, Michael, "Michael Zenner's Carnivorous Plants", 1999

Photos courtesy of Hydes Stove-House, Phone: 1-727-822-7632.

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