Food Web

The pitfall traps of S. purpurea arise from pitcher-shaped leaves that fill with rainwater, where insects drown if they fall in. Most other species of pitcher plants rely on digestive enzymes to decompose insects that have fallen into the leaves and they have leaves that are usually closed or with an umbrella-like hood protecting the digestive enzymes from diluting in rainwater. The leaves of S. purpurea are unique in having a hood that is open, encouraging rain to gather inside, and insects to drown in the water. For this species, the digestion of insects is primarily done by bacteria that arrive into the leaves from the surrounding environment. The bacteria are consumed by different protozoan species, a rotifer (Habrotrochus roseii in North America), and an aquatic mite (Sarraceniopsis gibsonii), which are in turn consumed by larvae of a mosquito (Wyeomyia smithii). The mites and mosquito are specialists that occur primarily in S. purpurea, as do the larvae of two other dipterans, a fleshfly (Fletcherimyia fletcheri) and a midge (Meteriocnemus knabii). In the non-native range of Europe, the fleshfly, midge, and mosquito larvae are absent from the food web and no other types of dipteran larvae are present. Although the relationship between the host plant and its inquilines has been proposed to be everything from mutualistic to parasitic, the true nature of the relationship may be context dependent.