40 Fun Facts About Symbiosis

The isopod Cymothoa exigua enters a snapper through its gills and ends up replacing which body part?

Tongue tissue dies once the isopod's claws cut off its blood supply, and the animal then grips the stub and sits in its place. The fish can use the intruder like a prosthetic.

The slender pearlfish hides from predators by slipping inside the rear end of which seafloor animal?

Sea cucumber breathing does the work: the animal draws water in through its anus, so the pearlfish only has to wait for the door to open. Most of these lodgers do their host no harm.

Which tiny animals of the genus Demodex live unnoticed in the hair follicles around human eyelashes and noses?

Mites of two Demodex species live on human faces, and one DNA study found them on every adult it tested. They crawl over the skin at night and usually cause no trouble at all.

Which zombie video game series based its outbreak on Ophiocordyceps, a real fungus that hijacks ants?

The Last of Us imagines the fungus jumping to humans. In real rainforests it steers an infected ant to climb a plant and lock its jaws onto a leaf, then grows a spore-filled stalk out of the ant's head.

Which fish, coated in a protective layer of mucus, lives unharmed among the stinging tentacles of sea anemones?

Clownfish gain a home that few predators dare enter, and they pay rent by driving off anemone-eating fish and fanning their host with their fins.

Burdock burrs, which spread by hitching harmless rides on animal fur, inspired which everyday fastener?

Velcro began when Swiss engineer George de Mestral took a close look at the burrs stuck to his dog's fur and copied their tiny hooks. The plant gets its seeds carried away, and the animal loses nothing.

Which bird lays its eggs in the nests of reed warblers and dunnocks, leaving them to raise its chicks?

Cuckoo chicks heave the host's own eggs over the rim of the nest with their backs, so the foster parents pour all their effort into feeding one giant impostor.

Which tree-dwelling rainforest mammal has grooved fur that grows green algae, helping to hide it from jaguars?

Sloth fur is a small ecosystem of its own: besides the algae that tint it green, it shelters moths found nowhere else but on these animals.

Which Christmas plant grows on tree branches and steals their water and nutrients through a root-like organ?

Mistletoe still makes some food with its own green leaves, so it is only a part-time thief. Birds spread it by wiping the sticky seeds off their beaks onto fresh branches.

Which deep-sea fish dangles a lure that glows thanks to light-making bacteria living inside its tip?

Anglerfish owe their glow to the bacteria packed into the lure's tip. The lure itself is a modified fin ray that draws prey within reach of the fish's jaws.

Bees get nectar and flowers get pollinated: which term describes a partnership where both species gain?

Mutualism is nature's win-win deal, and it has steered evolution: the shapes of many flowers exist largely to suit the animals that carry their pollen.

Which term, from Latin for 'sharing a table', describes one species benefiting while the other is unaffected?

Commensalism covers orchids perched on tree branches and birds nesting in tree holes: the guest gains a home, and the host barely notices.

A flea drinks a dog's blood and gives nothing back: which term describes one species living at another's expense?

Parasitism differs from hunting because the freeloader is far smaller than its victim and usually keeps it alive, often staying in or on the same host for a long time.

First used in biology by a German fungus expert in the 1870s, the word 'symbiosis' comes from Greek for what?

Living together is all the Greek roots promise, which is why biologists count any close, lasting bond between species, whether it helps, harms or makes no difference to the partners.

Which African bird perches on rhinos, zebras and giraffes, eating the ticks buried in their skin?

Oxpecker visits are not pure kindness: the birds also peck at wounds to keep them open and drink the blood, which is why some biologists class them as freeloaders.

Which fish uses a sucker on top of its head to hitch rides on sharks, turtles and whales?

Remora suckers are a dorsal fin reshaped into a ridged oval disc. Sliding backward tightens the grip, and swimming forward breaks it.

Which crusty growth on rocks and tree bark is really a fungus with algae housed inside its body?

Lichen pairs a fungus that provides the body with algae that make food from sunlight, a team tough enough to live on bare rock, in hot deserts and across the Arctic tundra.

Which sea animals house zooxanthellae, tiny algae that feed them sugars made from sunlight?

Corals turn ghostly white when overheated water makes them throw out the algae, an event known as bleaching. The algae provide much of the colour as well as the food.

Rhizobia bacteria living in the root nodules of peas and beans capture which element from the air for the plant?

Nitrogen gas is useless to plants until the bacteria turn it into ammonia. In return the plant feeds its lodgers with carbon-rich acids.

Which shelled filter-feeders fix themselves to the skin of humpback and gray whales for a free ride?

Barnacles on a whale are carried through food-rich water without any effort, and a single humpback may haul up to 450 kg of them at no real cost or benefit to itself.

Which cell parts are thought to descend from bacteria swallowed by a larger cell long ago?

Mitochondria still carry their own small loop of DNA and split in two on their own schedule, much as free-living bacteria do.

Which plant cell structures are thought to descend from free-living cyanobacteria engulfed long ago?

Chloroplasts divide in a way that closely resembles their free-living relatives, a likeness one botanist noticed as early as 1883, long before DNA could back him up.

Which biologist argued that cell organelles began as bacteria in a paper rejected by about fifteen journals?

Lynn Margulis finally saw the paper printed in 1967. As a young graduate she had married the astronomer Carl Sagan, and she later wrote popular science books with their son Dorion.

Which term, from Greek for 'fungus root', names the underground partnership between fungi and most land plants?

Mycorrhiza is a trade: the plant hands over sugars made in its leaves, and the fungus pays with water and minerals such as phosphorus drawn from the soil.

Which tropical American insects grow underground fungus gardens, feeding the crop with vegetation they carry home?

Leafcutter ants use the greenery as compost for a fungus that feeds their larvae. Next to humans, they form some of the largest and most complex societies on Earth.

Which thorny trees house ant colonies inside hollow thorns and are defended by them against leaf-eating animals?

Acacias of the bullhorn kind pay their guards with nectar and protein-rich leaf tips. The ants repay them by attacking browsers and clearing away seedlings that might grow up to shade the tree.

Which sap-sucking garden insects are stroked by ants to release honeydew, earning protection in exchange?

Aphids are treated like a tiny dairy herd: the ants stroke them with their antennae to release drops of the sugary waste and drive away the predators that come to eat them.

Which small reef fish greets larger fish with a dance, then picks dead tissue and pests off their skin?

Cleaner wrasse work from fixed stations that their 'clients' visit, and a waiting fish will hold a special pose so its groomer can reach the gills and even swim into its mouth.

Which wood-eating insects depend on microbes in their guts to break down the tough cellulose they swallow?

Termites owe their diet to gut microbes that turn wood fibre into fuel the insects can absorb. DNA shows these colony builders are really a branch of the cockroach family tree.

Bacteria living in the human large intestine make a form of which nutrient, needed for blood to clot?

Vitamin K takes its letter from 'koagulation', the Danish word for clotting. Gut bacteria such as E. coli make its K2 form, and newborns are given an injection of the vitamin to prevent bleeding.

Rats carrying Toxoplasma gondii lose their aversion to the smell of which predators, where the microbe breeds?

Cats are the only animals in which the microbe can reproduce sexually, so a rat that strolls up to one delivers it home. It can infect almost any warm-blooded animal, humans included.

Which flat, segmented worm has no mouth or gut and absorbs digested food through its skin inside an intestine?

Tapeworm heads carry hooks or suckers that anchor them to the gut wall while food flows past. A lone worm can even fertilise itself when no partner shares its host.

Which disease is caused by Plasmodium, a single-celled invader of red blood cells spread by mosquito bites?

Malaria needs two hosts: the microbe multiplies quietly in the human liver before bursting into the blood, where the next biting mosquito picks it up and carries it onward.

Which African bird leads people to wild bees' nests, then eats the wax left after the raid?

Honeyguide birds answer a special summons: Yao honey-hunters in Mozambique call them with a trilled 'brrrr-hmm', and a hive is far more likely to be found when they use it.

Which white wading bird follows buffalo, horses and tractors to snap up the insects they disturb?

Cattle egret flocks spread around the world alongside livestock farming. The birds were first sighted in the Americas in 1877, having apparently flown across the Atlantic.

Which burrow-digging crustacean shares its home with a goby that keeps watch and signals danger with its tail?

Pistol shrimp keep an antenna resting on their sharper-eyed lodger whenever both leave the burrow, so one flick of the fish's tail sends the pair diving for cover.

The Hawaiian bobtail squid feeds glowing bacteria in a light organ to hide what from predators below?

Its silhouette vanishes because the glow matches the light falling on the squid from above, a trick called counter-illumination. The bacteria are paid in sugar and amino acids.

Giant tube worms have no mouth or gut as adults and live on bacteria-made food beside which deep-sea features?

Hydrothermal vents pour out hydrogen sulfide, which the bacteria packed inside each worm use as fuel to build food. The worms were first encountered in 1977, on an expedition to the Galápagos Rift.

Cows rely on microbes in which stomach compartment, the largest of four, to ferment tough grass fibre?

Rumen microbes ferment roughage that a mammal's own digestive juices cannot break down, turning it into fatty acids and usable energy. Farmers know the chamber by a plainer name, the paunch.

Which word describes a symbiosis that a partner cannot survive without, as with gutless tube worms and their bacteria?

Obligate partners die apart, while 'facultative' ones merely do better as a pair. An adult tube worm has no way to eat, so without the microbes inside it the animal would starve.