While this relationship can play out in many surprising ways, there are three main types of symbiosis seen in nature. Here's how to tell them apart.
Mutualism
Mutualism is one of nature’s best examples of teamwork. In a mutualistic symbiosis, both parties get something out of the deal and are better equipped for survival because of their arrangement. Take for instance the live sharksucker (Echeneis naucrates), a species of fish that attaches itself to sharks, whales, and other marine animals and keeps them clean by eating smaller parasites. In exchange for its hygienic help, the sharksucker is protected from predators wary of getting too close to its larger hosts.
Commensalism
In commensalism, one species benefits while the other isn’t harmed. In fact, commensal symbiotes can often be overlooked by their hosts. Take for example, Demodex folliculorum, a tiny species of mite found on almost all human faces. These microscopic creatures live out their three-week or so lifespans in your pores and hair follicles. There’s not a lot to recommend them, exactly, but they also don’t bother anyone except in extreme cases, where they can contribute to skin problems. To learn more about the microscopic creatures ling in and on your body, visit the special exhibition The Secret World Inside You.
Parasitism
Parasites live off of a host, causing irritation and distress while contributing nothing in return. Blood feeders like the common bedbug (Cimex lectularius) are some of the most easily recognized parasites, but blood is far from the only way they parasites take from their hosts. While it’s not noble, parasitism is an effective way of making a living, so much so that nearly every animal species is the host to at least one kind of parasite. Even parasites themselves host free riders, like the bacterium Wolbachia, which lives in bedbugs, though new research suggests it may play a more complicated symbiotic role than once thought.