Insects make up to 90% of all animal species on the planet, and most of them can be found in the tropics, the regions around the equator. Yet we still know surprisingly little about how these species will cope with rising temperatures driven by climate change.
I am an animal ecologist, studying how organisms respond to climate change. My research aims to provide a better understanding about whether and how insects might be affected by heat. I was part of a team of scientists who studied more than 2,000 insect species along elevational gradients, from lowland areas up to high mountain regions, in Kenya and Peru.
Using a field experiment, we measured the heat tolerance of insects across many different groups. This is important because most previous studies either combine inconsistent datasets or focus on a single species.
Our goal was to understand how entire insect communities respond to heat. We looked at a large variety of insects, such as flies, bees, beetles, butterflies and grasshoppers, to name just a few.
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We found that many are likely to face dangerous levels of heat stress. This was true even under conservative assumptions, including the possibility that species move into cooler habitats.
In parts of tropical Africa, where temperatures are already high and rising quickly, this could put large numbers of species at risk. Flies are the most vulnerable group. Our findings suggest that many tropical insects, especially those in lowland regions, are already living close to their thermal limits and may struggle to survive further warming.
Tropical regions, including much of Africa, contain the greatest diversity of insect life on Earth. The loss of these species would have far-reaching consequences for ecosystems, agriculture and human well-being.
Insects are essential to ecosystems – and to people. They play a key role in food production through pollination. While bees are the best-known pollinators, ants, flies and beetles also make major contributions. They are also nature’s recyclers. Dung beetles, for example, break down waste and carcasses, helping prevent the spread of disease and maintaining healthy soils.
Insects also form the backbone of food webs. They are both predators, such as dragonflies hunting mosquitoes, and prey for birds, reptiles and mammals. Without insects, ecosystems would quickly begin to fail.
Mountains as natural laboratories
To understand how insects respond to temperature, we used mountains in Kenya and Peru as “natural laboratories”. Despite being on different continents, these countries share key features: they lie in the tropics, have steep mountain ranges, and host exceptionally high biodiversity.
Air temperature decreases predictably with elevation, allowing us to study how species cope with different thermal conditions across short distances. In Kenya, this meant working from hot lowland savannas to cooler highland forests. The study was carried out from Watamu to Mount Kenya, including the Taita Hills. In Peru, the gradient ranged from the lowland Amazon region, including some parts of Manu National Park, to the high Andes close to Cusco.
Read more: African mountains are feeling the heat of climate change
We collected insects manually, trying to cover the entire community and include a large diversity across the major insect groups. For each single individual, we measured what is known as the critical thermal maximum: the temperature at which an insect loses motor control due to heat stress. To do this, we gradually increased temperature until each insect entered a heat coma.
We then compared these limits with real-world temperatures, using both field measurements and satellite data. This allowed us to calculate “thermal safety margins” (how close species are to the temperatures they can tolerate).
The results were striking: insects, such as dung beetles, from lowland areas already live very close to their thermal limits, while insects from higher elevations overall have a greater buffer, meaning they could possibly adjust to more heat.
We found that some insects can temporarily increase their heat tolerance through short-term physiological responses, such as producing heat shock proteins – special molecules that help protect and stabilise their cells when temperatures rise. But we found that this ability is limited in insects living at low elevations.
Insects from mid- and high elevations could slightly increase their heat tolerance after prior exposure to heat. In contrast, lowland insects showed little to no such capacity. This is worrying, because these are the species already experiencing the highest temperatures.
To understand why some insects tolerate heat better than others, we also used a deep learning model to predict the stability of their proteins.
We found that insect groups with more heat-stable proteins also had higher heat tolerance. For example, flies tended to have lower tolerance and less stable proteins, while grasshoppers showed higher tolerance and more stable proteins.
This suggests that heat limits may be constrained by fundamental protein architecture. This means that many species may not be able to evolve fast enough to keep pace with rapid climate change.
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We then explored the potential consequences of future warming. Using climate projections up to 2100, we compared expected temperatures under different scenarios with the heat limits of lowland insects.
Results and relevance
Extreme heat can kill insects within seconds. But even lower levels of heat stress can have long-term effects, reducing reproduction and causing population declines.
Insects can sometimes avoid heat by moving into cooler microhabitats, such as shaded vegetation, forest understories or soil. This makes habitat complexity critically important. In African landscapes, intact forests, savannas and shrublands can provide these thermal refuges. But habitat loss and fragmentation reduce these options.
Maintaining climate corridors, connections between cooler and warmer areas, will be essential to allow species to move and survive.
Our findings suggest that many tropical insects are already close to their limits. Without strong action to limit global warming and protect habitats, climate change could push them beyond survival. The consequences would not only be ecological but could deeply affect society on many levels.
Kim Holzmann, Postdoctoral researcher at the University of Würzburg, at the Department of Animal Ecology and Tropical Biology, Julius Maximilian University of Würzburg