Insects trapped between extreme heat and cold in Peru’s Amazon

By day, the beaches of the Madre de Dios river in south-eastern Peru are scorching. When exposed to the sun, the sand can reach 45C. Nothing moves.

Beneath it, the small dung beetle Canthonidia rubromaculata waits to emerge. It has a few hours to find and mould capybara droppings into balls on the Amazonian riverbank and roll them home, before the heat drives it underground once more.

These beetles rely on dung for food, but rising temperatures are shrinking their scavenging window.

“A river beach is not simply an empty stretch of sand,” says Elena Chaboteaux, a researcher at the Los Amigos Biological Station in Madre de Dios, run by the NGO Conservación Amazónica. “For some species, it is the only world they have.”

That world is heating up. Peru’s Amazon already experiences more than 100 days a year where the heat index exceeds 41C, according to the Peruvian Geophysical Institute (IGP). By 2050, that figure could rise to more than 300. For the beetles, which cannot survive in temperatures above 45C, this is a crisis.

Elena Chaboteaux, a researcher at the Los Amigos Biological Station in Madre de Dios, explains that even small changes in temperatures can affect all the things insects do for the forest (Image: Diego Pérez Romero)

“Extremes are becoming more frequent,” says José Marengo, a climatologist and researcher with the Intergovernmental Panel on Climate Change. He points out that this also includes increasingly common cold waves.

By pollinating plants, breaking down organic matter and moving nutrients, insects sustain the processes on which the Amazon rainforest depends. And they are not immune from the extreme weather patterns wrought by climate change and El Niño weather formations. “A small change in temperature can affect everything they do for the forest,” Chaboteaux explains.

A limit drawing ever closer

The Manu Biological Station in Cusco, southern Peru is also run by Conservación Amazonica, and has been establishing just how much heat the dung beetle can withstand. The team measured the temperature of the beaches and nearby forest across six months, then brought Canthonidia rubromaculata into the laboratory and gradually increased the heat.

Their findings were published this July. On average, the dung beetles began to suffer at 31.75C, and reached their limit at around 45C. The beaches where they live already reach those temperatures.

“It is not just that they reach lethal temperatures. Stress begins much earlier,” explains Alejandro Lopera-Toro, the station’s scientific director and a co-author of the study. “For an insect, a day at 40C means it cannot leave its hiding place at any point.”

The Manu Biological Station in Cusco, southern Peru. Having spent six months measuring its heat tolerance, the team established that the dung beetle Canthonidia rubromaculata begins to suffer at 31.75C and reaches its limit at around 45C (Image: Diego Pérez Romero)

Alejandro Lopera-Toro, scientific director of Manu Biological Station, sets up a Mothbox monitor at the facility. These automated devices use ultraviolet light and cameras to photograph nocturnal insects without having to capture them (Image: Diego Pérez Romero)

Unlike mammals, insects cannot sweat or pant to cool down, and body temperature regulation is generally rudimentary if not impossible. This makes them more susceptible to the effects of extreme heat.

Heatwaves in the Peruvian Amazon are becoming more frequent, longer and more intense, explains Marengo. According to the National Meteorology and Hydrology Service (Senamhi), Madre de Dios and its fellow Amazonian department of San Martín both experienced temperatures above 40C in 2024 – Peru’s warmest year in six decades. The wider Amazon region averaged 15 nocturnal heatwaves that year.

Another study published this year (also co-authored by Lopera-Toro) assessed the heat tolerance of around 2,300 insect species in Peru and Kenya. In Peru, flies were found to succumb first, at 39C; beetles at 41C; and grasshoppers at around 45C. If humanity’s CO2 emissions remain high, half of the species studied may not survive to the end of the century, based on projected temperatures.

Grasshoppers from the predominant Acrididae family. A study co-authored by Lopera-Toro assessed the heat tolerance of around 2,300 insects in Peru and Kenya, including grasshoppers (Image: Diego Pérez Romero)

The dung beetle Oxysternon conspicillatum. In Peru, the study found that beetles succumbed at 41C, and grasshoppers at around 45C (Image: Diego Pérez Romero)

“Their entire life cycle is disrupted, and they cannot change it from one year to the next,” explains Marengo.

Cold at the wrong time

It is not just heat that insect populations must contend with. Cold waves are increasingly arriving out of season. Peru recorded 30 in 2025. This is the highest number since 2008, when Senamhi’s data begins.

While the overall trend is towards warming, Marengo says the impacts of cold waves are severe.

Fog shrouds the rainforest early in the morning during a cold wave in Madre de Dios. Peru recorded 30 cold waves in 2025, the highest number since Senamhi began recording this data in 2008 (Image: Diego Pérez Romero)

Researchers studying the impact of a cold wave at Los Amigos in June 2023 found that most insect activity recovered fairly quickly. Dung beetles were among the exceptions and appeared to be more harshly affected. In the same study, 47% of the insects subjected to heat tests did not survive.

The study warns that an “increased intensity” of cold waves under future climate scenarios could threaten tropical insects, which are poorly adapted to deal with the lower temperatures. It is “crucial to gain a better understanding of the impact of cold waves in the tropics”, the study concluded.

It is not just beetles that are particularly affected. Geoffrey Gallice has spent nearly a decade studying butterflies at Finca Las Piedras, a research centre in Madre de Dios run by the Alliance for a Sustainable Amazon. On a normal day, each trap (baited with fermented banana) catches around 25 butterflies and moths. Gallice says the traps are almost empty during a cold wave.

Biologists lay traps for butterflies in the forest near the Finca Las Piedras research centre. On a normal day, each trap catches around 25 butterflies and moths, but during a cold wave the traps are almost empty (Image: Diego Pérez Romero)

A Zaretis butterfly caught at Finca Las Piedras. Unusual temperatures can cause some butterflies to stop reproducing (Image: Diego Pérez Romero)

A broken calendar

Luis Tayori, a knowledge holder and elder of the Harakbut Indigenous community, used to recognise the arrival of cold weather when the cético tree (Cecropia membranacea) bore fruit. As per Harakbut knowledge, the forest provides a calendar of signs that herald meteorological shifts. “Animals would devour the leaves and fruit. They became docile and could not escape – that was when we would hunt them,” Tayori recalls. “But that calendar has broken down.”

Luis Tayori, an elder of the Harakbut community, notes that as per Indigenous knowledge, the forest provides a calendar of signs that herald meteorological shifts. But that calendar has broken down, he says (Image: Diego Pérez Romero)

Hundreds of kilometres from Harakbut territory towards the centre of Peru, the Asháninka people, one of the largest Indigenous groups in the Peruvian Amazon, have their own calendar. In the communal reserve that bears their name, park ranger and Indigenous scientist Richar Demetrio used certain frogs and the stars to detect the signs of a cold wave. But these signs are becoming harder to read. “We used to know exactly when it was coming,” he says. “Now we no longer do.”

Senamhi recorded 13 of 30 cold waves arriving out of season in 2025. Five of those came in March, the middle of Amazonian summertime. Meanwhile, Marengo recalls a heatwave coming in June 2024, the middle of winter. “These events are falling outside the classical definition,” he notes.

This disordered calendar has impacts for insects, too. Sixto Cruz, a beekeeper at the Madre de Dios apiary Widi Da, has raised bees for 40 years. He says they are now affected by the weather: “When they should be working, they stay tucked away because of the cold, and that affects the pollination of flowers.”

He now finds dead bees outside their hives. “That never used to happen.”

A nest of Tetragonisca weyrauchi stingless bees, raised by Sixto Cruz in Madre de Dios. He says that because of the cold he now finds dead bees outside of the hives: “That never used to happen.” (Image: Diego Pérez Romero)

Butterflies, meanwhile, take their cues to reproduce from the seasons. At Finca Las Piedras, Lizett Retuerto, Geoffrey Gallice and other scientists found that unusual temperatures can cause some butterflies to stop reproducing. “The female is able to detect that variation and physiologically pause reproduction,” Retuerto explains. “If the climate becomes unpredictable, the mechanism falls out of sync.”

Without refuge

When heat or cold becomes extreme, an insect has only one option: hide. The forest allows it to do so, explains Lopera-Toro. “Its ground is covered with leaf litter, organic matter and roots,” which buffers both extremes.

But between 2001 and 2025, Madre de Dios lost almost 368,000 hectares of forest, according to Peru’s environment ministry. Across the Peruvian Amazon as a whole, the loss exceeded 3.3 million hectares. “For a small species, digging 10 cm means moving its entire world,” Lopera-Toro explains.

A Ficus insipida tree in Madre de Dios. Between 2001 and 2025, over 3.3 million hectares of forest in the Peruvian Amazon was lost, according to the country’s environment ministry (Image: Diego Pérez Romero)

A single butterfly species can disappear and the forest will still stand. But insects are “the puppeteers of the networks that make the forest work”, Lopera-Toro adds. If several species disappear, those networks begin to unravel.

In the Asháninka communal reserve, Demetrio is already seeing the signs. During a cold wave, butterflies stop flying and remain motionless on leaves, unable to seek the nectar they depend on or pollinate forest trees. Without them, fruit does not develop. “When many butterflies die, we already know that pollination will not be as effective the following year,” he says. “If these species disappear, in 15 or 20 years there will be no food for us.”

On the beaches of Madre de Dios, the dung beetle is still waiting. Each night, as the sand cools, it emerges to push its ball of dung. It has a few hours before the heat returns. For now, those hours are still enough.

This report was produced with support from the Pulitzer Center.

Article thumbnail: A moth caterpillar of the Saturniidae family (Image: Diego Pérez Romero)