Flatworms are important in the maintenance of healthy levels of algae, protozoans and zooplankton in various pond environments. Because flatworms consume all of these types of organisms, they control the population and keep the organisms from spiraling out of control.
Most freshwater flatworms live in ditches, streams, lakes, ponds and puddles, choosing to burrow under plants, rocks and other debris to stay out of direct sunlight. The lifespan of the flatworm is unknown in the wild, but members of one flatworm species ranged between 60 and 140 days while under study in captivity. Flatworms are remarkably hardy, with the ability to shrink down to their original hatching size when they do not have enough food but then to grow back to their adult size when they receive food again.
While flatworms are durable within their environment, pollution places flatworms at risk, along with other species. If flatworms and other consumers of zooplankton and algae are not numerous enough to control the populations, the algae can spread significantly, taking light and oxygen away from other species in the pond. Zooplankton are an important element in a pond's food chain, and managing their population levels is important for maintaining balance at all levels on that chain.