Symbiotic Partnerships

Symbiosis: A term coined for biology by Anton de Bary in 1879 to describe different species living in close partnership; mutualistic alliances shaped the history of life, from the first complex cells to coral reefs and forests.

Lynn Margulis: Her theory that mitochondria and chloroplasts were once free-living bacteria swallowed by other cells was reportedly rejected by around 15 journals before it was published in 1967; it is now textbook biology.

Clownfish: A coating of mucus lets it live among a sea anemone's stinging tentacles unharmed; the fish gets protection while chasing off anemone-eating fish and feeding its host with scraps and nutrients.

Pistol Shrimp: The nearly blind shrimp digs and maintains a burrow it shares with a goby fish, keeping an antenna on the goby, which flicks its tail to warn of danger so both can dart inside.

Yucca Moth: The female deliberately gathers yucca pollen and packs it into a flower's stigma after laying eggs there; the plant gets pollinated and the larvae eat only some of the seeds.

Fig Wasp: Most of the hundreds of fig species depend on their own specialized tiny wasp to pollinate them, a partnership that dates back tens of millions of years.

Leafcutter Ant: These ants do not eat the leaves they cut; they use them to farm a fungus that feeds the colony, part of an ant agricultural tradition tens of millions of years older than human farming.

Greater Honeyguide: In Mozambique, Yao honey hunters call this bird with a special trill, and it leads them to bees' nests; the humans take the honey and the bird feasts on the leftover wax.

Oxpecker: Long seen as a helpful tick-remover for rhinos and buffalo, it also pecks at wounds to drink blood and keep them open, making the relationship far messier than it looks.

Egyptian Plover: Herodotus wrote that this bird cleans crocodiles' teeth, and the story is repeated endlessly, but there is no reliable scientific record of it ever happening.

Bluestreak Cleaner Wrasse: It runs cleaning stations where fish line up to have parasites removed, serving more than 2,000 clients a day, and in 2019 it became the first fish reported to pass the mirror test.

Hawaiian Bobtail Squid: It houses glowing Vibrio fischeri bacteria that cancel out its shadow in moonlight, and every dawn it expels most of them so the colony can regrow by night.

Zooxanthellae: These microscopic algae live inside reef-building corals and supply most of their energy; when stressed by heat, corals expel them and turn ghostly white, the process called bleaching.

Riftia Pachyptila: The giant hydrothermal vent tubeworm has no mouth or gut; it relies entirely on bacteria inside its body that turn toxic sulfide into food.

Pompeii Worm: Living on scalding deep-sea vent chimneys, it wears a fleece of bacteria on its back that may help insulate it from some of the hottest temperatures any complex animal endures.

Bullhorn Acacia: This tree grows hollow thorns for aggressive ants to live in and feeds them with nectar and protein-rich tips; in return, the ants attack any animal or plant that touches it.

Trichonympha: Termites cannot digest wood on their own; these single-celled organisms in their guts, along with bacteria, break down the cellulose for them.

Buchnera Aphidicola: This bacterium has lived inside aphids for so long that it has lost many of its own genes; neither partner can survive without the other.

Rhizobium: These soil bacteria move into root nodules of peas, beans and clover and pull nitrogen from the air, the reason farmers rotate legumes to fertilize fields naturally.

Lichen: Long described as a fungus and an alga living as one, it surprised scientists in 2016 when researchers found many lichens also contain a third partner, a yeast.

Suzanne Simard: Her research suggested trees share carbon through underground fungal networks, popularly called the 'wood wide web,' though other scientists argue the idea has been overstated.

Calliactis Parasitica: Hermit crabs place this sea anemone on their shells for stinging protection, and when the crab moves to a bigger shell, it carefully transfers the anemone too.

Spotted Salamander: Its eggs contain a green alga, and the alga has been found inside the embryo's cells, the only known case of a photosynthetic partner living inside vertebrate cells.

Three-Toed Sloth: It hosts algae that tint its fur green as camouflage, and moths that live in its fur lay eggs in its dung, one theory for why the sloth risks a weekly climb down to the ground.

American Badger: Coyotes and badgers sometimes hunt ground squirrels together; the coyote chases prey above ground while the badger digs it out below, and a 2020 video of the pair went viral.