But as much as a tapeworm or a blood fluke may disgust us, parasites are crucial to the worldâs ecosystems. Their extinction may effect entire food webs, perhaps even harming human health.
Parasites deserve some of the respect that top predators have earned in recent decades. Wolves were once considered vermin, for example â but as they disappeared, ecosystems changed.
Scientists realized that as top predators, wolves kept populations of prey in check, which allowed plants to thrive. When wolves were restored to places like Yellowstone, local ecosystems revived, as well.
Researchers have begun carefully studying the roles that parasites play. They make up the majority of the biomass in some ecosystems, outweighing predators sharing their environments by a factor of 20 to 1.
For decades, scientists who studied food webs drew lines between species â between wildebeest and the grass they grazed on, for example, and between the wildebeest and the lions that ate them.
In a major oversight, they didnât factor in the extent to which parasites feed on hosts. As it turns out, as much as 80 percent of the lines in a given food web are links to parasites. They are big players in the food supply.
Parasites can control populations of their hosts. Some are killed outright; other hosts, once infected, cannot reproduce, which would divert resources that the parasite craves to eggs or sperm. Some parasites move from host to host by making prey species easier for predators to kill.
So if these horrendous pests are major players in ecosystems that we want to save…