Ninety years ago this month, Australia embarked on an ambitious but ultimately ill-fated experiment in biological control.
In 1935, Queensland sugar cane farmers faced a relentless enemy—the cane beetle. These voracious insects burrowed into sugarcane roots, devastating crops and threatening an industry vital to the nation’s economy. Desperate for a solution, scientists at the Bureau of Sugar Experiment Stations (BSES) looked to overseas biological control methods for inspiration. Their attention turned to the cane toad, a species thought to have effectively managed pests in Puerto Rico and Hawaii. With minimal environmental assessments, they imported and released 2,400 of these warty warriors into the fields of Gordonvale, Queensland, convinced they had found a natural pest control solution.
What came next was one of Australia’s most significant ecological disasters.
The rise of the sugar cane industry in Queensland
Sugar cane was first brought to Australia by the First Fleet in 1788, but commercial production didn’t really get going until the mid-19th century. While sugar cane was first planted in New South Wales in 1923 at Port Macquarie, Queensland’s warm, humid climate proved ideal for sugar cultivation. By the 1860s, plantations were thriving along the fertile coastal regions.
While John Buhot produced the first pound of granulated sugar from cane planted in the Brisbane Botanic Gardens in 1862, Captain Louis Hope commercialised the sugar industry by planting 20 acres in Cleveland, Brisbane, in the same year. He brought in indentured labour from the Pacific Islands to develop his plantations. Within months, sugar companies were established in Brisbane, Maryborough, and Mackay.
Hope established Queensland’s first sugar mill in Cleveland in 1864. He pioneered commercial cultivation and crushing of sugar, selling the first ton of Queensland raw sugar in 1866. This progress set the stage for the industry’s rapid growth, aided by the employment of indentured Pacific Islanders as labourers.
By the end of 1869, 28 mills were processing cane from 5,000 acres. From 1875 to the 1890s, 36 sugar mills and 14 juice mills were built in the Bundaberg district alone to crush sugar cane from the nearby plantations. During this time, large sugar plantations were set up, including estates ranging from 4,000 to 8,000 hectares managed by the Colonial Sugar Refining Company (CSR).
Battling the cane beetle
The sugar industry faced ongoing challenges, including labour shortages and pests threatening crops. However, the most significant pest was the cane beetle.
Native to Australia, these beetles initially fed on indigenous vegetation. However, the clearing of forests and the expansion of cane fields created an irresistible food source. The larvae of the beetles—cockchafer grubs or scarab beetles—burrowed underground. They found the leaves of the cane stalks highly appealing and began laying their eggs on the ground around the cane plants. The eggs developed into grubs that migrated until they reached the roots of the cane, which they fed on, weakening the stalks and causing them to collapse.
By the late 19th century, the industry had become so essential to the economy that the Queensland government stepped in to support its growth and safeguard the sugar industry from the cane beetle’s destruction. They established the BSES in 1900. Headquartered in Brisbane, it boasted stations spread across the cane-growing regions. The bureau provided advisory services and operated research laboratories for the sugar industry to assist in finding solutions to growers’ challenges. This research facility was dedicated to investigating sugar cane cultivation, pest management, and improving industry efficiency.
The cane beetle problem worsened during the 1890s Depression when sugar prices plummeted, resulting in the implementation of every conceivable control method. Children were enlisted to hand-pick larvae, and by 1899, over 50 tons of beetles had been collected in the Mackay district alone. However, this wasn’t a sustainable solution. Other methods were equally ineffective, such as light traps and shaking beetles from trees.
Entomologists and agricultural scientists worked tirelessly to find solutions to the cane beetle problem. They initially experimented with chemical controls. Chemical fumigation using a noxious and foul-smelling compound called carbon disulphide was attempted but proved costly and hazardous. It was carried in knapsacks and sprayed every 20 centimetres or nine inches. The process was slow and laborious, taking one man an entire week to cover a third of an acre in the hot, humid conditions. Illness was widespread, and farmers struggled to attract labour for the task.
Another method was trialled to capitalise on the beetle’s phototropic behaviour—its attraction to light. It involved a large white metal panel fitted with a funnel at the bottom, leading to a kerosene tin. The light was turned on next to a feeding tree, like a weeping fig, and then the panel was shaken to entice the beetles into flight towards the light. They would collide with the panel and fall into the kerosene tin. Other farmers would handpick the beetles from their cane.
However, those methods wouldn’t remove the beetles from cane fields. The government, BSES, and farmers urgently needed an effective pest control strategy. Entomologists turned to the emerging field of biological control.
The birth of biological control
In the 1920s, entomologists worldwide investigated biological control, a burgeoning scientific field focused on using natural predators to manage pest populations.
In Australia, during the humid mid-summer of 1920, a young war veteran from North Queensland, Alan Dodd, settled into his new vocation as an entomologist, studying the behaviour of cane beetles near Gordonvale. After sunset on cloudless nights, shortly following a period of rain, he observed and documented the copulation antics at dusk and the egg-laying of female beetles during the pre-dawn hours under moonlight. This work made it abundantly clear that biological control of cane beetles would require a specialised predator poised to attack them in the half-hour just after dusk, following rain, and half an hour before dawn.
Progress on tackling the cane beetle issue stalled after Dodd was recruited by the Commonwealth Prickly Pear Board to help manage the unchecked spread of the prickly pear cactus. While Dodd contributed to the innovative biological control program successfully eradicating the pear problem, the cane beetle challenge remained unresolved.
Under the guidance of Cyril Pemberton, an entomologist with the Hawaiian Sugar Planters Association (HSPA), Hawaii became a world leader in biological control during the 1920s. Pemberton oversaw several successful introductions of biological control agents to Hawaii, including the mirid bug from Fiji to manage the sugar cane leaf hopper; the Australian fig wasp to pollinate Hawaiian figs; and the larvae of a tiny parasitic wasp from the Big Scrub rainforests that targeted fern weevils ravaging tree ferns in Hawaii. These releases, along with many other exotic insects, were carried out without any bureaucratic hurdles or prior testing.
However, one pest problem still eluded Pemberton: the anomala grubs, a type of scarab beetle that fed on the roots of sugar cane. Although a scolid wasp from Japan initially controlled the anomala beetle, the pest reemerged in 1930, causing extensive damage. Pemberton attended the 1932 Fourth Congress of the International Society of Sugar Cane Technologists in Puerto Rico, keen to learn about a potential solution to his ongoing issue.
The Puerto Rican solution
Meanwhile, an Australian from BSES was also on his way to the conference primarily to present the results of BSES’s latest work. Arthur Bell, the deputy director of BSES, was, like most of his entomological peers, a veteran of the Great War and was selected for a leadership role upon his return home to Queensland. He was one of only three men chosen for overseas training on a sugar research travelling scholarship and prepared for a leadership position in the latest technologies.
After being away for four years, during which he earned a master’s degree at Berkeley in California, a diploma at the Royal College of Science in London, and travelled through the USA, Central America, Puerto Rico, China, Japan, and the Philippines, Bell spent an additional four months at the HSPA Experimental Station in Hawaii. Back in Queensland, he led investigations into the scientific breeding of sugar cane.
Puerto Rican cane farmers first faced problems with yellowed, wilting stalks after sugar cane production doubled in the decade leading up to 1911. They eventually identified the culprit: a scarab beetle known as May beetles. However, they encountered the same challenges as sugar cane farmers worldwide—how to combat the devastation of their crops. After years of unsuccessful attempts to manage the beetle, an Experimental Station was established on the north coast at Rio Piedras to find a natural predator for the May beetles that were destroying their cane stalks. Although no natural predators were found, numerous insects were imported to eradicate the scarab cane beetles, but all efforts failed.
Suddenly, a dozen “Surinam” toads, Bufo marinus [now Rhinella marina], from Barbados, were released into the southwestern sugar cane fields of Puerto Rico in 1920. They quickly adapted to their new environment and began breeding. In 1923, a director from the Puerto Rican Experimental Station observed the toads consuming May beetles and other insects beneath the glow of a lamp at a Jamaican wharf while he waited for a boat to take him home. That night, another forty toads were collected and released at Río Piedras.
By 1932, the toad had spread across Puerto Rican cane fields, and scientists believed it was consuming the cane beetles, leading to a decline in their numbers and the flourishing of the cane fields. Entomologist George Wolcott declared it a major success and claimed the farmers’ problem had been solved:
This is one of the few instances on record of a foreign predator being entirely successful in the control of a native insect pest and, to date, the toad has developed no serious undesirable habits.
It didn’t matter that his conclusion was based entirely on observation, lacking any experimental work to confirm that the toad was indeed eating the beetles. This information was presented at the 1932 Conference, where the leading entomologist of the time, Raquel Dexter, showcased the “success” of introducing the “Surinam” toad from the Caribbean into Puerto Rico in the 1920s.
Her research demonstrated that the toad was a predator of the cane beetle after conducting stomach dissections on 301 toads. She strongly argued that it was an effective biological control agent for the beetle, despite the lack of experimental evidence confirming that the beetle had disappeared because of the toad. From the perspective of the local sugar cane industry and the scientists at the Rio Piedras Experimental Station, the toad arrived, and the beetles vanished.
Meanwhile, Pemberton faced immense pressure from his boss to introduce the “Suranim” toad into Hawaii. However, he rightly wanted to learn more about the toad to ensure it wouldn’t become a pest there. He remained in Puerto Rico after the conference and was eventually persuaded by Dexter to take the plunge and introduce the toad to Hawaii. In March 1932, he and his colleagues collected 34 toads to bring home. As Nigel Turvey eloquently notes in his book on the toad:
In the Leap Year [of 1932], it was the great leap forward for Bufo marinus. With the first shipment, the genus Bufo would leave the Caribbean to become established in the Pacific – something 40 million years of anuran evolution, 80 million years of volcanic activity in the Pacific Ocean, and the 450 million years of continental drift had been unable to do.
Bell missed Dexter’s presentation because he was busy delivering his papers. He didn’t see Dexter’s work until a year later and was cautious—so cautious that farmers demanded quick action while the beetles continued to ravage their sugar crop. Meanwhile, Pemberton wrote an article celebrating the introduction of the toad into the sugar plantations of Hawaii.
Under immense pressure, BSES ultimately relented. They applied to the Commonwealth for permission to import the toad, showing that it would only consume night-flying insects. Since all the pests in the sugarcane fields were night flyers, permission was granted.
By 1935, the responsibility for action lay with the young but confident entomologist Reg Montgomery, who was stationed at the Meringa Station (the “grub” station) in Gordonvale. In April 1935, Montgomery flew to Hawaii and, with Pemberton’s help, collected 102 toads for introduction to a specially designed pond at Gordonvale, where they would stay until their release at the start of the wet season later that year. While waiting, they bred successfully and abundantly in captivity, producing many tadpoles in preparation for their release to eliminate the cane toad beetle.
In August 1935, batches of 100 to 500 toadlets were dispatched to designated locations in the Mulgrave and Hambledon districts. At this time, the toad from the Caribbean had become widely known as the cane toad.
The Unintended Consequences
The cane toads thrived—but not as intended. Instead of controlling cane beetles, they ignored them altogether, favouring an omnivorous diet that included native insects, small mammals, and one another. Worse still, these invaders arrived armed with a deadly secret weapon: potent toxins secreted from glands on their backs. This defence mechanism rendered them nearly invincible in the Australian ecosystem. Native predators—quolls, goannas, freshwater crocodiles, and even domestic pets—perished in droves after ingesting the toads.
People who had nothing to do with cane farming started reporting that their pet dogs were foaming at the mouth after contact with a cane toad. They were advised to wash the dog’s mouth, assuring them it would be fine. Any complaints were scoffed at, ignored, and considered unwarranted.
If only, in 1932, scientists had scrutinised Raquel Dexter’s work with greater scepticism and asked harder questions, this disaster might have been avoided. Dexter’s conclusions—that the cane toad had successfully controlled May beetle populations in Puerto Rico—were based more on assumption than rigorous scientific evidence. No controlled experiments were conducted to determine whether the toads were genuinely responsible for the decline in beetle populations, nor was baseline data collected on beetle numbers before the toad’s introduction. A closer examination might have revealed the truth: the toads were not a reliable solution to sugar cane pests, and introducing them to Australia would be a grave mistake.
Suspicions of a significant failure emerged, beginning with Walter Froggatt, the president of the New South Wales Naturalist Society. He was the first to publicly question the introduction of the cane toad. The Federal Health Department, under the ministry of Joe Lyons, was established in the 1920s with quarantine as its primary focus. Under the leadership of the experienced Director General Dr. John Howard, the department banned the toad, permitting it to roam only in the Cairns, Gordonvale, Innisfail, and Tully areas where it had already been released.
Montgomery publicly criticised and mocked Froggatt’s views on the toad, portraying him as a crank. He then shifted his focus to overturning the government’s ban. He supplied the government with studies from autopsies indicating what the toad was consuming and contended that it was not insects beneficial to the environment. The ban was lifted in October 1936, allowing for toad liberations and dispersals in all the sugar cane districts of coastal Queensland.
Despite mounting evidence of ecological harm, the sugar industry remained steadfast in its support for the toad. BSES annual reports continued to praise the toad’s “effectiveness” in pest control, even as reports indicated that cane beetle populations remained unaffected.
At the 1938 Cane Pest Board Conference held at Meringa Station, Montgomery sought a resolution to protect all cane toads under government law after reports surfaced of toads being killed to safeguard domestic pets. While it wasn’t supported, the delegates expressed frustration over the misguided actions of an “uninformed” public.
By 1940, things began to unravel. It was clear that the toads had failed in their intended role. Toads spread out from the dry, red volcanic soils of the cane fields, and reports indicated that there were more cane beetles than ever. The tragic reality became apparent: cane toads consumed all the ground-dwelling insects. However, cane beetles were not ground-dwelling insects. If a beetle was in the cane fields without ground cover, cane toads avoided that area and the direct sunlight. Instead, the toads preferred congregating around streetlights, licking up hapless insects that fell to the ground. Rather than solving the beetle problem, they created an entirely new ecological crisis.
The spread of the cane toad was relentless. Lacking natural predators in Australia, they multiplied rapidly, expanding beyond Queensland into New South Wales, the Northern Territory, and Western Australia at a rate of up to 60 kilometres per year. Their ability to breed in still water—such as ponds, ditches, or livestock troughs—ensured their continued expansion.
By the 1950s, the cane toad was officially recognised as an ecological threat rather than a saviour. However, by that time, the damage had already been done.
Nature strikes back – the predator’s revenge
For decades, cane toads reigned supreme. People in Queensland recount stories of their childhoods when these bloated amphibians lounged in gardens like toxic landmines, unbothered by humans or wildlife. But nature, ever adaptable, found a way to strike back.
Some of Australia’s most intelligent predators began evolving tactics to outsmart the toads. Crows, known for their remarkable problem-solving skills, learned to flip the toads over and feast on their toxin-free underbellies. Large predatory lizards that had once suffered heavy losses developed an instinctive aversion to them. Even freshwater crocodiles selectively preyed on juvenile toads that had lower toxin levels.
Over time, the unchecked proliferation of toads began to slow in areas where predators had adapted. The once-common sight of dinner plate-sized toads covering suburban lawns became rarer. While they still represent a significant presence in northern Australia, their uncontrolled expansion has diminished.
Lessons Learned
The cane toad’s saga serves as a cautionary tale about the dangers of introducing foreign species for biological control. Unlike the successful eradication of the prickly pear by introducing the ectoblastic moth, the cane toad experiment underscored the risks of ecological interference without thorough environmental assessments.
Today, scientists continue to explore ways to reduce the toad’s impact, including developing targeted biological controls and studying predator adaptation. However, the reality remains: the cane toad is here to stay. Australia will forever bear the scars of this well-intentioned yet disastrously misguided amphibian invasion.
Good article, thanks Robert.
What about the cane beetle? Did they find a solution for them or are they still a pest?
It is a good question, Andre and I probably should have addressed that in the blog, although I wanted to focus solely on the toad.
In one word, the answer is insecticides, and potent ones at that.
Apparently, the cane beetle is still Australia’s most significant economic pest of sugarcane. The most common method of controlling them is via an insecticide called imidacloprid, which has been used since 2001. Before that, it was benzene hexachloride (BHC), specifically the formulation known as “Gammexane”. Gammexane was used in 1945 and was sprayed before the beetle flight. It was considered a godsend for the industry until it was banned in 1987. Before that, the control method promoted soil fumigation with paradichlor in carbon bisulphide.
Andre, see https://sugarresearch.com.au/pests/canegrubs/ for current situation.
A good summary Robert about interesting times. Easy to be wise after the event.The saga of biological control of several agricultural pests (prickly pear, lantana, cane toads to mention a few), in the early mid 20th C involving government laboratories in Qld and NSW backed by the Commonwealth is a story in itself. You mention a book by Nigel Turvey on cane toads; can you give us all the reference please? Was the army’s attempt to shoot out emus in the WA wheatbelt (The Great Emu War of 1932) an attempt at biological control?
Ian, Nigel Turvey’s book is “Cane Tads: a tale of sugar, politics and flawed science”, Sydney University Press, 2013. He provides a much more in-depth analysis that I can’t achieve in my short blog version.
Yes, I agree that being wise after the event is easy. However, I outline how experienced and cautious entomologists decided to accept flawed scientific work.
My blog on emus, published in May 2023, provides some details about the Emu War of 1932. I never thought of it as biological control, but I guess you could classify it as a crude form.
A good read, thank you, Robert. One of my memories of those revolting toads includes you with your friends and golf sticks!!