Explained
You scratch my back, and I’ll scratch yours. Nature is rife with examples of species that derive mutual benefit from – and are sometimes entirely dependent on – their interactions with each other. Experts refer to these reciprocal relationships as mutualism in nature.
What is the difference between mutualism and symbiosis?
Although these terms are often used interchangeably, there is a subtle difference between them. Mutualism is always a two-way street where both parties benefit, while symbiosis also includes interactions where one species profits at the expense of the other (parasitism), as well as situations where only one species benefits, but without harming the other (commensalism).
Examples of symbiotic relationships between species
- Mutualism: Ants feed on the honeydew produced by aphids and protect them in return.
- Commensalism: Cattle egrets follow wild and domestic cattle, feeding on the insects they disturb while grazing.
- Parasitism: Rafflesia, the world’s largest flower, takes water and nutrients from the host plant it grows on.
Most people are aware of everyday examples of mutualism in nature. Flowers rewarding bees and other insect pollinators with a nectar bribe, for example. Oxpeckers hitch a ride on giraffes and other African herbivores, using their specially adapted flattened bills to pick off ticks and other parasites. In a classic example of mutualism in the ocean, clownfish shelter unharmed among the stinging tentacles of an anemone, in return for protecting their protectors from the nibbling jaws of butterflyfish.
There are myriad weird and wonderful examples of animals that work together, including mind-boggling mutualism between plants and animals. Here are eight of our favourites.
The corpse flower, Rafflesia arnoldi. © Jeremy Holden / Fauna & Flora
Rafflesia's massive petals unfurl after the bud bursts from the stem of the host vine inside which the parasitic plant has been developing unseen.
Honey badgers, honeyguides and humans
The internet is fascinated by honey badger facts – usually relating to their ability to hold their own in a fight versus a lion or another large predator – but what about their relationship with honeyguides? According to popular myth, these beeswax-loving birds lead honey badgers to a hive. The latter uses its powerful claws to break open the bees’ nest and the two animals share the spoils. Eyewitness accounts of this interaction are hard to find, but the best evidence comes from Tanzania. What we do know for certain is that mutualism between honeyguides and humans is well-established. The bird calls to attract the attention of its human collaborator, then flies ahead, guiding them to the hidden honey trove, often deep in the forest. After smoking out the bees and breaking open the nest, the human collects the honey, leaving the honeyguide to feast on the grubs and beeswax.
Honey badger feeding on honeycomb. © Dominic Cram
A Honey badger feeding on honeycomb. © Dominic Cram
Greater honeyguide feeding on beeswax. © Dominic Cram
Greater honeyguide feeding on beeswax. © Dominic Cram
Milk me, don’t eat me
Many butterflies in the Lycaenid family have a fascinating symbiotic relationship with ants. The common oak blue caterpillar, for example, is protected from predators and parasites by green tree ants while it munches on the leaves of its foodplant. But there’s no such thing as a free lunch. The caterpillars pay their bodyguards in bodily fluids – specifically, a sugary secretion that oozes from glands on their backs. Some Lycaenid butterflies, including UK species such as the silver-studded blue and large blue, are entirely dependent on ants to complete their life cycle. But these relationships don’t always benefit both partners. Large blue caterpillars secrete a honey-like liquid to attract foraging red ants, which carry them back to their nest. Once underground, the caterpillars gorge themselves on ant grubs before hibernating. They pupate in springtime before emerging as adult butterflies and making their escape.
Large blue butterfly, a threatened species. © ADEPT
The large blue butterfly cannot complete its life cycle without the help of red ants.
Taken to the cleaners
At coral reef cleaning stations, cleaner wrasse and cleaner shrimps attend to the larger fish and turtles queuing up for a full-body valeting service. To avoid being eaten, the cleaners perform a carefully choreographed dance and wait for a signal that it’s safe to approach. Once a big fish opens its gill covers and mouth, they work inside and outside their customer, picking off and eating sea lice and other parasites, as well as food remains, dead skin and fungus.
Tomato grouper being cleaned by cleaner shrimps. © Zafer Kizilkaya
Cleaner shrimps performing a crucial cleaning service for a tomato grouper. © Zafer Kizilkaya
Cape collaborators
Relative to its size, South Africa’s Cape Floral Region harbours more species of native plant than even the richest tropical rainforest, including all the world’s proteas. The aptly named Cape sugarbird is also confined to this landscape. It has a mutualistic relationship with protea flowers, feeding almost exclusively on their nectar and acting as their main pollinator. The birds time their nesting to coincide with the flowering season and seek out other food sources only when the proteas have finished blooming.
Cape sugarbird feeding on limestone sugarbush. © Juan Pablo Moreiras / Fauna & Flora
Cape sugarbird feeding on a limestone sugarbush.
With friends like these, who needs anemones?
Clownfish are not the only marine creatures to collaborate with anemones. It’s no secret that hermit crabs protect themselves by squeezing their softer, more vulnerable body parts into a discarded shell. But one resourceful hermit crab species takes personal protection a stage further by collecting anemones and attaching them to its mobile home. The venom in the anemones’ tentacles deters crab-eating predators such as octopuses from approaching too closely. The anemones benefit by feeding on scraps from the crab’s meals. When the hermit crab outgrows its home, it finds a larger shell, dislodges the anemones from the old one and places them on top of its new house before taking up residence.
Hermit crab covers its shell with small sea anemones for camouflage and protection. © dynamofoto / Adobe stock
The anemone hermit crab covers its shell with small sea anemones for camouflage and protection.
Woolly bats and pitcher plants
Pitcher plants – named for their vase-like leaves – usually grow on nutrient-poor soils. To overcome this food shortage, they have evolved to become meat-eaters. Unwary insects, lizards and even small mammals are attracted to these carnivorous plants by a combination of striking colours, alluring perfume and nectar treats. The rim of the pitcher is so slippery that visitors lose their footing and fall into a pool of liquid. The pitcher produces digestive juices – basically an acid soup – that dissolve its prey and turns them into plant fertiliser. Not all animal encounters end quite so gruesomely, however. In another extraordinary example of mutualism in nature, woolly bats on the island of Borneo use a particular species of Nepenthes pitcher plant as a safe daytime roost. In return, the bats deposit their droppings before they crawl out of their snug sleeping bags at dusk, providing the pitcher with vital nutrients.
Hardwicke's woolly bat and pitcher plant. © Merlin Tuttle
This tiny Hardwicke's woolly bat will enter and roost in the pitcher. The plant will feed on the bat's droppings.
Underground networking
The mutualistic relationships that have evolved between fungi and the roots of trees and other plants are known as mycorrhizae. With their roots connected via a vast network of tiny fungal threads, plants can communicate and support each other by sharing water and nutrients. Payback for the fungus comes in the form of the sugars produced by the plants during photosynthesis. We are only just starting to understand the complex interdependency between fungi and plants, but it’s surely one of the wonders of the natural world. Fauna & Flora is actively promoting agroforestry initiatives that harness the potential of mycorrhizae on the Nicaraguan island of Ometepe and at other project sites.
Fungi in a forest. © Stephanie Foote / Fauna & Flora
Hidden beneath this fruiting body is a vast subterranean network of filaments connecting fungi and plants roots as part of an extraordinary symbiotic relationship.
Fig wasp – an overlooked, irreplaceable insect
One of the most remarkable examples of mutualism between plants and animals is found in strangler figs and their minuscule but mighty pollinators. A tiny female fig wasp enters through a hole in a ripening fig fruit, carrying pollen from the male flowers in the fig where she was born. As she lays her eggs inside the fruit, she pollinates its female flowers. The wasp larvae develop inside the fig. The blind, wingless males emerge first. Once they have found a female and mated, their final act is to dig an escape hatch for their mate. The winged females push their way out and fly to another fig, picking up pollen from the male flowers as they leave.
Typically, each fig species can be pollinated only by a single species of wasp. Tree and insect have co-evolved to match each other perfectly, meaning that the extinction of one would prove terminal for the other. Strangler figs are one of the most important food sources in tropical forests, crucial to the survival of gibbons, hornbills and countless other species. Losing them would have a disastrous knock-on effect on seed dispersal, forest regeneration, ecosystem health and carbon storage. A tiny, seemingly insignificant insect is playing a pivotal role in the wider forest landscape. Without it, the entire ecosystem would collapse.
Fig wasp female emerging through an opening in the fig that has been cut by a male wasp. © Tim Laman / Nature Picture Library
A female fig wasp emerges through an opening in the fig fruit cut by a male wasp, from where she will fly to another fig, transferring pollen to its flowers in the process.
Helmeted hornbill. © JT Jeeraphun / Adobe Stock
A helmeted hornbill feasting on the ripe fruit of a strangler fig that has been pollinated by a fig wasp. All three species are inextricably bound together in a complex mutualistic relationship.
Making the connection
The rich tapestry of life on Earth is held together by the complex relationships unfolding in nature every minute of every day. Every single species, however small, plays a crucial role in ensuring that the threads don’t unravel.
The future of our planet depends on safeguarding this bountiful biodiversity, and we depend on your support to help us protect it.
DonateLarge blue butterfly, a threatened species. © ADEPT
Related Content
Species
Hornbills
Hornbills are under threat from deforestation and hunting. Find out more about these extraordinary birds and how we can ...
Explained
Uncloaking nature’s most talented traitors – Species that have mastered the art of deception
Intriguing examples of craftiness, deception and dishonesty in nature. Creatures camouflaged, the harmless mimicking the...