From the moon jellyfish to the humble garden snail, invertebrates play a central – and often invisible – role in shaping our world. Numbering in their millions, species of insects, arachnids, snails, crustaceans, corals, jellyfish, sponges and echinoderms are among the least understood animals on Earth, often overshadowed by their vertebrate cousins.
We asked scientists to tell us about how invertebrates shape our world and structure its ecosystems – and the unforeseen consequences of their disappearance.
‘Nobody likes to step in poo’: decomposing world waste
Without shrimp, dung beetles and thousands of fly species, vast amounts of organic matter would not break down and the nutrients would not be recycled through ecosystems. Many invertebrate species feed and breed in the waste of plants and animals, and play a vital role in their healthy functioning.
“Nobody likes to step in poo when out for a walk and we often complain there is too much about – but things would be far worse without dung beetles and green bottle flies, both of which consume and break down animal poo removing the odour and creating fertiliser for our soils,” says Paul Hetherington, director of Buglife.
In the oceans, mussels, clams and lobsters are all important decomposers, while species such as sea cucumbers also play a role akin to earthworms.
“Burrowing sea cucumber that move through the sediments as part of their daily activities help to oxygenate them, which is important for numerous other processes,” said Annie Mercier, of Memorial University of Newfoundland, and co-chair of the International Union for the Conservation of Nature (IUCN) species survival commission sea cucumber specialist group. “Sea cucumbers are not only active recyclers, they are prey to many other animals, including crabs, fishes, turtles, sea otters, pinnipeds, eider ducks and more.”
Caffeine-hit blossoms and shrinking pansies: invertebrates shaping the plant world
Bees are famously crucial pollinators of human staples. But beetles, flies and other invertebrates are also essential for helping plants fruit and reproduce. One in every three mouthfuls that humans eat is the result of pollination, researchers estimate. The role of invertebrates shapes the way plants behave and evolve – such as coffee and citrus trees, that give insects a reward in return when they visit their flowers.
“Coffee and citrus flowers produce caffeinated nectar, which has a pharmacological effect on honeybees and bumblebees – it enhances their memory for the unique smells emanating from flowers and so helps the bees find these important food sources in complex floral landscapes,” says Prof Phil Stevenson, head of trait diversity and function at Kew Gardens. “In doing so, it helps the flowers get pollinated as the bees are more likely to return,” he says.
Many plants have evolved to attract particular species of invertebrates, such as prosopanche plants that are native to South America. The group produce heat to woo small nitidulidae beetles to spend the night inside them. When pollinators disappear, it can also change plants – a study in December found French wild pansies were producing smaller flowers and less nectar as pollinator numbers declined, effectively giving up on scarce insects and evolving to self-pollinate, scientists said.
Dave Goulson, a professor of biology at the University of Sussex who specialises in bee ecology, said the disappearance of pollinators was already having dramatic consequences in some parts of the planet.
“In parts of south-western China there are almost no pollinators left, and farmers are forced to hand-pollinate their apples and pears, as otherwise their crops would fail. In Bengal I have seen farmers hand-pollinating squash plants, and reports are coming in of farmers in parts of Brazil resorting to hand-pollinating passion fruits,” he wrote in his recent book Silent Earth.
Breaking down plastic waste
Invertebrates could help break down some of the billions of tonnes of plastic waste that humans produce every year. In 2022, researchers found that the larvae of the Zophobas morio, a beetle species, were capable of digesting polystyrene and successfully completed their lifecycle.
“Within 48 hours … the faeces they produce turn from their usual brown – when they eat bran – to white,” said Dr Chris Rinke of the University of Queensland, a co-author of the study.
Architects of the coral reefs
More than half a billion people depend on reefs around the world for food, protection and their livelihoods. They are natural barriers to storms, flooding and erosion, safeguarding human settlements, while also providing a home for thousands of fish species. Invertebrates are crucial reef builders, but they are threatened by the climate crisis.
“Reef-building hard corals are the architects of coral reefs – they create the physical structure of a reef as new corals grow on the skeletons of dead corals. On a diverse reef, the growing and eroding matrix of old and new skeletons results in complex structures and spaces, creating three-dimensional habitat for the myriad species living on a reef,” says David Obura, founding director of Cordio east Africa and head of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES).
Corals are not the only reef-building animals, says Julia Sigwart, a member of the IUCN species survival commission mollusc specialist group, who warns that marine invertebrates risk being overlooked.
“Marine invertebrate animals comprise the vast majority of the species diversity in the ocean, including many species that are not yet described or named. Because they are not so familiar to us humans, we often lump groups together; many people do not realise that sponges are animals, let alone that there are thousands of different species,” she says “This leaves a huge risk that species are going extinct before we even know that they are there, with surprising and potentially disastrous consequences.”
Upturning predator food chains
The spread of invasive invertebrates can have major consequences for the whole ecosystem. In January, a study found that the arrival of invasive big-headed ants in Kenya had set of an ecological chain reaction that led to lions making fewer zebra kills. Tree cover had fallen in areas where the big-headed ants had spread, providing less cover for lions to ambush zebras. Researchers said their findings had a global lesson about the importance of invertebrates.
“Although ants might seem small and unimportant, for holding together entire ecosystems this couldn’t be further from the truth. This recent study shows that native mutualistic ants are the fabric that holds together the African savanna,” says evolutionary biologist Dr Corrie Moreau, an expert on ants at Cornell University’s Moreau lab.
“When the native ants are displaced from their plant partners by invasive species this causes ripple effects across the entire landscape,” she says. “It is amazing to think that the small but mighty ant can influence the diets of top predators.”
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