Insects and us: a mind-blowing 20 quadrillion ants and what they mean for the planet

There are 2.5m of these tiny creatures for each human and they play a big role as ecosystem engineers, as well as providing insights on everything from the climate to ageing

To most of us, they are small, uninteresting and sometimes annoying, but 2022 revealed just how ubiquitous ants are and how indispensable they are to the planet. Scientists revealed in September that there are an estimated 20 quadrillion (or 20 million billion) ants globally – that’s 2.5 million for every person on the planet.

More than 12,000 known species of ant live in all sorts of habitats, from the Arctic to the tropics and they represent one of the most diverse, abundant and specialist groups of animals on the planet. Leafcutter ants are fungus farmers, slave-making ants capture broods to increase their work force, while wood ants herd aphids to the juiciest parts of a plant to harvest their honeydew sap.

Dr Sabine Nooten and behavioural scientist Dr Patrick Schultheiss, of the University of Würzburg, who were lead authors of the research, have drawn up a global map of ant abundance and are now investigating how ants have been influenced by factors such as climate, habitat destruction, urbanisation and agriculture.

“Are any of these things potentially driving higher or lower numbers of ants?” asks Nooten. “Some studies span 80 years, so we can also extrapolate into the future to see [what might happen to ants if] the environment changes that much again.”

A narrow-headed ant (Formica exsecta), tending birch aphids.
There is potential for some predatory ants to be used in pest control – and they could be more successful than existing chemical treatments. Photograph: John Walters/PA

The two scientists point out that if ant numbers in a place aren’t known, as is the case across much of Africa, nothing else about those ants will be understood either. “There could be diversity in social structure, genetic or chemical diversity; this is all stuff we’re still finding out,” says Schultheiss.

Ants (Formicidae) are social animals that live in often complex colonies underground, in mounds or in trees. Each army of ants is headed up by a queen that lays thousands of eggs, and most ants seen above ground are the female workers, while males’ primary function is to mate with a new queen before they die. The new queen will then go on to start a new colony.

Experts agree that ants are ecosystem engineers because they play a crucial role in decomposing organic matter, recycling nutrients, improving soil health, removing pests and dispersing seeds. But, historically, ants haven’t attracted as much attention as crop pollinators, such as bees, which perhaps have more of an obvious economic value. That bias could soon change. Ants have been used as a biological pest control on citrus crops in China for centuries, and research published in August indicates that the pest control potential of some predatory ants could work better than some agricultural chemicals.

The wonders of ant biology throw up plenty of other possibilities for real-world applications. Queen ants that live more than 30 years – yet have the same genetic material as a short-lived worker ant – could teach us something about senescence. Nobody understands how queens store sperm for decades inside their bodies without any degradation, despite colonies living in different climates. Meanwhile, Schultheiss’ research into ant navigation – how they find food and how they behave when they get lost – could help build mathematical models that instruct a robot searching for missing people.

Leaf cutter Queen ant surveys her colony.
The resilience of ants and their complex colonies could provide insight into the climate crisis. Photograph: Doug Schnurr/Alamy

Looking back at how ants evolved can shed light on a huge array of other plants and animals, too. Butterflies that rely on ants to tend to their caterpillars could disappear if those ants are wiped out, says Corrie Moreau, a professor at Cornell University: “Nature is this intricate woven tapestry and if you pull one thread, you’ll never know which is the critical thread that makes the whole thing fall apart.”

When Moreau, an expert in myrmecology (the study of ants), studied under the late prominent biologist Edward O Wilson, she remapped the ant family tree and discovered that ant evolution is closely linked to that of plants. “As flowering plants spread across the globe, ants took advantage of this amazing ecological niche to start hunting new insects and tend sap-sucking insects for their honeydew, while plants developed specialist structures to keep the ants there, including sugar-water fountains and domatia [hollow chambers in the plant where ant colonies can live].”

The observations Moreau has made while dissecting thousands of ants under the microscope are leading her along a new path of inquiry. “The ants that were the hardest to break open, with the toughest armour, were either predatory or herbivorous with gut microbes,” says Moreau, who has used antibiotics to wipe out the ants’ gut bacteria and demonstrated that the bacteria not only synthesise essential amino acids but that the ant host is incorporating them into the cuticle, the protective, flexible layer that surrounds the ant’s body.

Extremely sharp and detailed study of an Ant head taken with a microscope objective stacked from many images into one very sharp photo.
‘We have only just begun to realise the ecological importance they have,’ says Corrie Moreau of the humble ant. Photograph: Tomas Rak/Alamy

This research could shed light on our own gut microbiomes. “We can’t experiment on humans with antibiotics then cut them open to see what happens to the gut inside. But ants are social organisms just like us, we can do manipulations on their simplified gut system, then watch what happens. We can introduce a pathogen and watch how quickly it spreads through a nest. In a social system, are there hubs where if it hits that then everyone gets infected? Are there social mechanisms that limit the transfer of those microbes? We can use ants to ask those questions.”

“Ants are going to be one of the critical systems to study to understand the impacts of climate change … not just because of what disappears, but because of what is resilient,” says Moreau. “We have only just begun to realise the ecological importance they have.”

Every ant scientist has a favourite species

• Australian desert ant (Melophorus bagoti)
“To look at, this nice large brown ant is nothing special but they can use the position of the sun as a compass cue, and learn to use visual landmarks like we do [to navigate], so they notice a big tree on the left or a small bush on the right. They’re fascinating,” says Patrick Schultheiss.

Florida turtle ant (Cephalotes varians)
“These ants live in hollow twigs up in the canopy and soldiers block their nest entrance with their giant dish-plate heads and only move to the side when another individual from their nest is available to take over,” says Corrie Moreau.

Green-head ant (Rhytidoponera metallica)
“They have this amazing structural colour, shining in metallic green-blue-violet. And if you go on a picnic, that’s the first one that comes, it’s so brave!” says Sabine Nooten.

Find more age of extinction coverage here, and follow biodiversity reporters Phoebe Weston and Patrick Greenfield on Twitter for all the latest news and features


Anna Turns

The GuardianTramp

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