What Happened to the Locusts? The Strange Science of Swarms and Silence
Every few years, a story flickers across the global news cycle that feels almost medieval. Drivers in the Sahara wind up their windows as a brown cloud of insects smashes into their windscreens. Iranian soldiers fan out across orchards with backpack sprayers. East African farmers watch their fields stripped to stubble in minutes. Then, just as suddenly, the locusts vanish, and we go back to forgetting they exist.
So what is actually going on? Why do locusts erupt in apocalyptic numbers some years and disappear for decades in others? And why has one of the most famous swarming species in history simply ceased to exist? The answers sit at a strange crossroads of behavioural science, climate volatility and the long shadow of human agriculture — and they matter more for Australia than most of us realise.
The insect that becomes a different insect
The most counterintuitive fact about locusts is that they are not really a distinct kind of grasshopper. They are ordinary grasshoppers that, under specific conditions, undergo what entomologists call "phase change" — a dramatic shift in colour, body shape, metabolism and behaviour triggered by crowding.
In their "solitarious" phase, locusts are shy, greenish, and easy to overlook. Pack enough of them into a small patch of vegetation and something extraordinary happens: their legs brush against each other, serotonin floods their nervous system, and within hours they begin transforming into the "gregarious" phase — yellow-and-black, gregarious, and irresistibly drawn toward other locusts. Multiply that across a landscape and you get the swarms that The Washington Post recently documented slamming into cars crossing the Sahara.
This Jekyll-and-Hyde biology is why locusts are so hard to predict. The same species can sit quietly in remote desert margins for years, then explode into continent-spanning swarms after the right sequence of rain.
Why the swarms keep coming back
Locust outbreaks follow a recognisable recipe: drought, then unusually heavy rain, then more rain. Dry conditions concentrate solitary grasshoppers into the few patches of moist soil where they can lay eggs. When the rains return, vegetation explodes, eggs hatch in dense bands, and crowding tips the population into its gregarious phase. If wet conditions persist across breeding cycles, what began as a local outbreak can balloon into a regional plague.
That is essentially the story the BBC told about the "biblical" desert locust plagues of 2020, when swarms tore through East Africa, the Arabian Peninsula and into South Asia. A series of unusual cyclones in the Indian Ocean had dumped rain on the Empty Quarter of Arabia, giving desert locusts perfect breeding conditions across multiple generations before anyone noticed. By the time the swarms reached Kenya, they were the worst in 70 years.
This is where the climate connection bites. Warmer oceans are producing more frequent and more intense Indian Ocean cyclones. That doesn't mean more locusts every year — locust biology is too jagged for that — but it does mean the unusual rainfall sequences that trigger outbreaks are becoming less unusual. The same logic applies to the Sahel, North Africa, and the Iranian plateau, where authorities have repeatedly been caught flat-footed by sudden eruptions.
When countries call in the army
The standard response to a locust upsurge is unglamorous and chemically intense: spray the breeding grounds before swarms form, and spray the swarms before they reach farmland. It is a race against insect biology, and it is expensive. The ABC has reported on Iran deploying its military to fight locust incursions threatening crops worth billions of dollars, a reminder that this is treated as a national security issue, not just an agricultural inconvenience.
The problem with the spray-and-pray approach is that it depends on early warning, cross-border coordination and political stability — three things that often collapse exactly when locust risk is highest. The Food and Agriculture Organization runs a global Desert Locust Information Service that maps swarm movements in something close to real time, but its work relies on field reports from countries that may be at war, broke, or both. Yemen has been a chronic blind spot in recent years for exactly this reason.
Newer tools are emerging. Biopesticides based on the fungus Metarhizium acridum can target locusts without poisoning everything else in the food web. Drones are being trialled for both surveillance and precision spraying. And researchers continue to chase the holy grail: a way to interrupt the serotonin-driven phase change itself, so populations never tip into swarming mode.
The ghost in the story: the Rocky Mountain locust
Here is the twist that makes the modern locust story even stranger. The most catastrophic swarming insect ever recorded — the Rocky Mountain locust, which once formed a single swarm estimated at 12.5 trillion individuals across the American West — is extinct. Completely gone. JSTOR Daily has explored how this "long-lost locust" disappeared within a generation, leaving entomologists baffled for more than a century.
The leading theory is brutally instructive. The locust's permanent breeding grounds were river valleys in the northern Rockies — the same valleys settlers ploughed, irrigated and grazed with cattle in the late 1800s. The insects could survive crop-destroying mega-swarms across half a continent, but they could not survive the destruction of a few hundred square kilometres of native habitat where the eggs overwintered. By around 1902, the species was gone.
The ghost of the Rocky Mountain locust is a reminder that locust populations are weirdly fragile at the source even when they look invincible in flight. It also suggests, uncomfortably, that the surest way to eliminate a locust is to wipe out the ecosystem it depends on — not a strategy anyone wants to repeat at scale.
Why Australians should care
Australia has its own locust problem and its own quiet success story. The Australian plague locust (Chortoicetes terminifera) periodically erupts across inland New South Wales, Victoria, Queensland and South Australia, with major outbreaks costing farmers hundreds of millions of dollars. The 2010 plague was one of the largest on record.
What Australia has done relatively well is coordination. The Australian Plague Locust Commission, established in the 1970s, monitors breeding grounds across state borders and intervenes early, when bands are still on the ground. It is exactly the kind of joined-up surveillance regime that countries on the desert locust frontline struggle to maintain. As climate variability sharpens — more intense La Niña rain pulses, longer droughts in between — that early-warning capacity will only become more valuable.
It is also worth remembering that locusts are not simply a disaster. In several cultures they are food, and a high-protein one at that. The UN has repeatedly floated insect protein as part of a more climate-resilient food system. The grim irony of a locust plague is that it converts a farmer's crop into roughly the same mass of edible insect — just in a form almost no supply chain is set up to capture.
The bigger picture
Locusts are useful to think with because they sit at the intersection of so many slow-moving forces: a warming Indian Ocean, fragile rural economies, the limits of pesticide-led agriculture, and the deep weirdness of an insect that can change its own personality when its neighbours get too close. They are not coming for Australia's cities. But the conditions that produce them — wild swings between drought and deluge, gaps in monitoring, brittle food systems — are the same conditions reshaping farming everywhere.
The question "what happened to the locusts?" turns out to have two answers. The swarms are still here, and getting harder to predict. And one of the greatest of them is gone forever, killed not by spray but by a plough. Both answers are worth holding in mind the next time a brown cloud appears on someone's dashcam.