Carnivorous Plants

Plants and insects have myriad relationships to one another.  Some are mutually beneficial, as when plants offer nectar to feed insects which in turn pollinate the plants.  Other relationships only benefit the insects when they feed on leaves, stems, and roots.  For carnivorous plants, preying on insects to fulfill their need for nitrogen and other nutrients benefits only the plants.

Pitcher plants are carnivorous, living in bogs and fens found in warm weather areas.  In North America, most species are found along the southeastern coastal states from Texas to West Virginia.  Bogs are depressions filled with rain or melted snow, while fens are similar but get their water from surface or groundwater.  Both types of wetlands are low in oxygen and nitrogen, very acidic, and often quite cold.  These characteristics slow down the rate of decay in the vegetation of the wetland, further reducing the availability of nitrogen which is a vital component of chlorophyll, the compound used by plants, along with water, carbon dioxide, and energy, to photosynthesize sugar for food. 

^{Tracy’s sundew, Drocera tracyi by Matthew Paulson, May 2022; Venus flytrap, Dionaea muscipula by Judy Gallagher, Jun 2022; White-topped pitcher plant, Sarracenia leucophylla, showing downward hairs by Aaron Carlson, Sep 2013}

Carnivorous plants use several strategies to attract and trap insects.  Pitfall traps have slippery faced leaves forming a funnel with a pool of digestive enzymes waiting at the bottom.  Downward facing hairs on the leaves make it harder for insects to climb out.  Some plants use an opposite strategy and cover their leaf surfaces with a sticky secretion, trapping any insects that land on them.  Still others have a leaf-like structure made of two halves that snap together when an insect lands on an inner surface, trapping the insect inside.  In both of the last two instances, digestive enzymes are then released to cover, kill, and break down the insect body for absorption by the plant.

Carnivorous plants are insect pollinated and must be able to attract pollinators without trapping them.  All of the plant species go through a dormant period as seasonal temperatures get cooler.  Traps die back and are regrown when warmer weather returns.  In several species, flowers bloom and attract pollinators with nectar, completing fertilization before traps develop.  Other plants separate the flowers and traps by a physical distance.  Traps usually lie close to ground level to attract crawling insects, and flowers are grown on top of tall stalks to attract flying insects.  A third method is to make the flowers less attractive to potential prey, and make the traps less attractive to potential pollinators.  This is achieved by using different colors, patterns, and scents on flowers and traps.

Whether you are growing these unique plants at home or viewing them in a botanical garden or out in the wild, some of the plants and their pollinators to watch for include the white-topped pitcher plant, Sarracenia leucophylla  and the two-spotted bumblebee, Bombus bimaculatus; the cobra lily, Darlingtonia californica and the mining bee, Andrena nigrihirta, Tracy’s sundew, Drosera tracyi and the metallic green sweat bee, Agapostemon sericeus, and the Venus flytrap, Dionaea muscipula and any of the hoverfly species, Toxomerus sp.