The huntsman's cup (Sarracenia purpurea) [sar a see' nee a pur pur ee' a] is an insectivorous plant found in acidic, nutrient-poor bogs in eastern North America. But the plant is more than just a small curiosity; it is the base for its own little ecosystem. The huntsman's cup is the only species of Sarracenia that does not produce digestive enzymes. Rather its leaves provide little swimming pools for bacteria. They produce the enzymes for the digestion. The plant saves having to use its limited source of nitrogen to make the enzymes.

The ascidia (urn shaped leaves) of the huntsman's cup are open to the sky. Rainwater would constantly dilute the enzymes costing the huntsman's cup valuable nitrogen replacing the enzymes. The huntsman's cup alters the pH of the rainwater within the ascidia until the fluid is about as acidic as vinegar. Acid-loving bacteria thrive in these little pools.

The ascidia have a number of other functions as well. These leaves must carry on photosynthesis so the plant can survive. They must produce nectar on the lip and inside the hood to attract the insect prey. The downward pointing 'hairs' and waxy walls of the leaf form the trap and insure that the prey will slip and fall. And the leaves secrete a wetting agent that causes most insects to drown.

Dr. Stephen B. Heard in a study of Sarracenia purpurea growing in Newfoundland, Canada found that these plants are part of a small but complex ecosystem called a processing chain. The processing chain is a commensal system, that is, each organism benefits from the presence of at least one of the other organisms. The leaves are home to the larvae of three insects that somehow escape drowning and digestion--a flesh fly maggot, a few midge larvae, and several mosquito larvae. In the far north of this Sarracenia's range each leaf is viable for about a year. The life cycles of the fly, the midges, and the mosquitoes coincide with the life span of the leaf.

The pitcher plant provides the lure and the trap. A flesh fly maggot floats near the surface of the fluid. The maggot tears apart insects that have fallen into the pitcher, consuming much of the prey. The midge larvae cannot eat large insects, so they scavenge their meals from the pieces the flesh fly leaves behind. The mosquito larvae are filter-feeders; they sweep up 'bug crumbs' and bacteria for their meals. And surviving bacteria thrive on any remaining debris. The huntsman's cup benefits for it absorbs excess nitrogen and other compounds that the insects and bacteria excrete.