Insects are the most common and widely found group of animals, making up about 90% of all animal species. In the 2010s, scientists began noticing that many insect populations were decreasing. These findings surprised many people, even though earlier studies had already shown that some pollinators, like bees, were declining. Some people have shared stories about seeing more insects in the past, such as when drivers notice more insects hitting car windshields. The reasons for the decline in insect numbers are similar to those causing other types of wildlife loss. These include destroying habitats, such as farming that uses a lot of land and chemicals, using pesticides (especially insecticides), introducing non-native species, and, in some areas, changes in climate. Another possible cause is light pollution, though more research is needed to understand this fully.
Most of the decline involves fewer insects in certain areas, though some species are completely disappearing. The decline is not the same everywhere. In some places, insect numbers have increased, and some types of insects are becoming more common worldwide. Not all insect groups are affected equally; bees, butterflies, moths, beetles, dragonflies, and damselflies are among the most impacted. Other insect groups have received less attention in research. Also, data from earlier years is often missing. In major studies, scientists estimate that between 10% and 40% of all insect species might be at risk of extinction, but these numbers are debated and not certain.
Studies show that in areas where insects are declining, their numbers have been dropping for many years. However, these trends were not noticed earlier because insects have received less attention compared to mammals, birds, and other vertebrates. One reason is that insects lack the "charismatic" appeal of other animals. In 2016, scientists found that 30,000 insect species live in Central Europe, but very few experts there study insects full-time. This lack of research is even more serious in developing countries. As of 2021, most studies about insect populations come from Europe and the United States, even though these regions contain less than 20% of the world’s insect species. In Africa, Asia, and South America, there are few long-term studies of insect populations, which are needed to understand global trends.
To help insects, some governments have created conservation plans. For example, in 2018, the German government started a program to protect insects. This program aims to create better habitats for insects in farmland, reduce pesticide use, light pollution, and pollution in soil and water.
Context
The fossil record of insects shows that they have existed for hundreds of millions of years. This record indicates that new insect species continue to appear while others go extinct. Occasionally, the fossil record also shows times when many insect species went extinct at once, likely due to natural events like volcanic eruptions or meteor impacts. The Permian–Triassic extinction event caused the largest loss of insect species, and the Cretaceous–Paleogene event caused the second-largest loss. After these mass extinctions, insect diversity returned over time as new species appeared more frequently, though recovery often took millions of years.
People have been concerned about a human-caused Holocene extinction since the late 20th century, though early concerns focused less on insects. A 2012 report by the Zoological Society of London stated that insect populations worldwide were declining, which affects pollination and food sources for other animals. The report estimated that about 20% of all invertebrate species are at risk of extinction, with species that move slowly or live in small areas being most vulnerable.
Studies showing insect decline have existed for many years, with one tracking a decline from 1840 to 2013. However, the 2017 reprint of a German study on nature reserves brought widespread media attention to the issue, with headlines like "Insect Apocalypse." Ecologist Dave Goulson told The Guardian in 2017 that human activities are making large areas of land unsuitable for many forms of life, possibly leading to major ecological problems. Many studies show that factors like population numbers, total weight, and variety of species are declining in some areas but not all. Most research has focused on insects such as butterflies, moths, bees, beetles, dragonflies, damselflies, and stoneflies. Different insect species respond to environmental changes in different ways, and it cannot be assumed that all insect groups are declining equally. Some species adapt to changes easily, while others struggle to survive.
In March 2019, the Entomological Society of America stated that there is not yet enough data to predict an imminent mass extinction of insects. They noted that some predictions about insect declines may have been exaggerated. Studies in Europe have shown declines in abundance and diversity for some insect groups, such as certain butterflies, moths, bees, and beetles. These trends contribute to an overall pattern of decline, though individual species within groups may show different trends. For example, some British moths are becoming more common. In other areas, some insect species have increased, though trends in most regions remain unclear. It is hard to assess long-term changes in insect numbers or diversity because historical data for many species is missing. Strong data to identify at-risk areas or species is especially lacking in Arctic and tropical regions and in most parts of the southern hemisphere.
In March 2019, Chris D. Thomas and other scientists responded to predictions of a major insect decline, stating that reports of insect extinction may be slightly exaggerated. They urged more coordinated efforts to address insect declines, supported by stronger data than is currently available.
Global estimates
A 2020 study that combined results from many other studies found that the number of insects living on land seems to be decreasing by about 9% every 10 years. At the same time, the number of insects living in freshwater areas, like lakes and rivers, appears to be increasing by about 11% every 10 years. This study looked at 166 long-term studies that included data from 1,676 locations around the world. It found that the rate of insect decline varied depending on where the studies were done. The researchers said this variation was a positive sign because it showed that local actions, such as conservation efforts, might help protect insect populations. The study suggested that the increase in freshwater insects could be partly due to efforts to clean up waterways, as well as changes caused by global warming and more nutrients in water. However, some scientists later criticized the study's methods, and the journal that published it issued a statement expressing concern about its findings.
In 2022, 66 researchers asked 3,331 scientists who had studied biodiversity in the past 10 years about the status of insect species. This group included 629 scientists who studied insects and other small animals that live on land and in water. On average, these scientists estimated that about 30% of these species (with uncertainty between 20% and 50%) are or have been at risk of disappearing (including species that have already gone extinct since the year 1500). Since insects make up most of the world’s small animals, this estimate likely applies to them as well.
A 2019 survey of 24 scientists who study insects on six continents asked them to rate the seriousness of the insect decline on a scale from 0 to 10, with 10 being the worst. All scientists rated the crisis as between 8 and 10.
In 2019, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) reported that global trends in insect populations are not fully understood, but rapid declines have been observed in some areas. The report noted that declines in insects like wild bees and butterflies have been widely reported, and some areas have seen sharp drops in insect numbers even without major changes to land use. However, the report said it is unclear how widespread these declines are globally. It also mentioned that the percentage of insect species at risk of extinction is uncertain, but early estimates suggest about 10% might be threatened. In 2022, some researchers pointed out a difference between this estimate and the 30% figure found in a survey of 629 scientists who study invertebrates. They called for more research on insects and other species that are very diverse but not well studied to better understand the situation.
Causes
Scientists do not fully understand the reasons for the decrease in insect populations, or how important each reason is. These reasons likely differ among different types of insects and areas of the world. A study listed the main causes in order of importance as follows: "(i) loss of natural habitats and conversion to farmland or cities; (ii) pollution, especially from synthetic pesticides and fertilizers; (iii) biological factors, such as diseases and non-native species; and (iv) climate change."
Light pollution also contributes to the decline. Other factors that may play a role include human-made noise, non-native species, and excess nutrients from fertilizers.
The increased use of insecticides and herbicides on crops has harmed not only insects that are not the target of these chemicals but also the plants that insects rely on for food.
For example, a 2017 review discussed a large study in Germany about insect population declines. It noted that the German study could not directly link the decline to climate change or pesticide use. However, it suggested that more intensive farming practices might have contributed.
Climate change and the arrival of non-native species that compete with local species can stress native species, making them more vulnerable to diseases. Plants grow faster in higher levels of carbon dioxide, but the extra plant material has fewer nutrients. While some insect species, like flies and cockroaches, may increase, the overall number of insects is estimated to decrease by between 0.9% and 2.5% each year.
Insects make up the majority of invertebrate species. A 2018 study in Science Magazine estimated that if global temperatures rise to 1.5°C, 2°C, or 3.2°C, more than half of insect species would lose over 6%, 18%, or nearly 49% of their natural habitats, respectively. These losses could lead to more than a 20% chance of extinction for many species within the next 10 to 100 years, based on IUCN criteria.
A 2020 study published in Science examined over 60 bee species across two continents. It found that climate change caused significant declines in bumblebee populations and diversity, independent of changes in land use. Comparing the "baseline" period (1901–1974) with the recent period (2000–2014), bumblebee populations in North America dropped by 46%, while those in Europe dropped by 14%. The most severe declines occurred in southern regions, where extreme warm years have exceeded the temperature ranges these species are adapted to.
A major review paper published in 2024 predicted that between 14% and 27% of insect species could go extinct by 2070 under the RCP 4.5 climate scenario, and between 23% and 31% under the RCP 8.5 scenario.
Methodology
Three main measures are used to track and report changes in insect populations:
- Abundance – the total number of individual insects. This can refer to the number of insects in a specific group, within a certain area, or the total number of insects worldwide (regardless of which species they belong to).
- Biomass – the total weight of all insects (again, regardless of species).
- Biodiversity – the number of insect species that are still alive. Depending on the situation, a decrease in biodiversity might mean some insect species have disappeared from a local area, or it might mean species have gone extinct globally.
Most studies that track insect declines focus on abundance, some on biomass, a few on both, and a small number on all three measures. Information about the loss of species diversity on a global scale is less common than data on declines in abundance or biomass. Scientists often estimate global diversity loss by using data about abundance or biomass. While some studies show that certain insect species have disappeared from local areas, it is difficult to determine how many species have gone extinct worldwide. In a 2019 review, David Wagner noted that the current extinction event is causing animal species to disappear at a rate 100–1,000 times faster than the natural background rate. Some studies suggest that insect species are also disappearing at a similar or even faster rate. Wagner suggests that while biodiversity loss is serious, the decline in the number of insects (abundance) will likely have the greatest impact on ecosystems.
In theory, the three measures can change independently. For example, a decrease in biomass might not mean fewer insects or fewer species if the insects are simply becoming smaller. In practice, however, abundance and biomass usually show similar trends. Changes in biodiversity are often, but not always, related to changes in abundance and biomass. Some studies have found cases where biodiversity increases while abundance or biomass decreases. For example, a 42-year study of insects in the Breitenbach stream near Schlitz, which is thought to have been unaffected by human-related causes except for climate change, found that while the number of insects decreased, the number of species actually increased, especially during the first half of the study.
Survey results for specific regions
The Rothamsted Insect Survey, part of Rothamsted Research in Harpenden, England, started monitoring insect suction traps across the UK in 1964. These traps, which operate 24 hours a day, are described as "like upside-down vacuum cleaners that continuously sample the air for migrating insects." Between 1970 and 2002, the amount of insect biomass collected in the traps dropped by more than two-thirds in southern Scotland, though it stayed the same in England. Scientists suggest that insect numbers in England may have already started to fall by 1970 or that the absence of insect predators allowed pests like aphids to increase.
A 2014 review found that 33% of 203 insect species studied by the IUCN showed declining populations, with differences across species groups. In the UK, 30 to 60% of species in each group had shrinking ranges. Insect pollinators, which are vital for 75% of the world’s food crops, are also declining globally in both numbers and variety. This decline is linked to the loss of plant species that depend on them in Northern Europe. Scientists refer to the human-caused loss of both vertebrates and invertebrates as "Anthropocene defaunation."
People who lived through the 20th century often remember seeing more insects in the past. For example, entomologist Simon Leather noted that in the 1970s, windows in Yorkshire homes were covered in tiger moths attracted to nighttime lights, but these moths are now rare in the area. Environmentalist Michael McCarthy also described "moth snowstorms," where large numbers of moths gathered so densely they looked like blizzards in car headlights, a sight that has disappeared.
In 2004, the Royal Society for the Protection of Birds organized a Big Bug Count, giving volunteers "splatometers" to count insects hitting car number plates. On average, volunteers found one insect per 5 miles (8 km), which was lower than expected.
In 2013, the Krefeld Entomological Society reported a major drop in the amount of insects caught in malaise traps across 63 nature reserves in Germany. A 2017 reanalysis showed a 76% decline in flying insect biomass over 27 years, with an 82% drop in midsummer. This decline was observed in all types of habitats and could not be explained by changes in weather, land use, or habitat features. Scientists noted that not only butterflies, moths, and wild bees are declining, but the entire flying insect community is affected.
In 2019, scientists highlighted a 2017 study showing a 76% drop in flying insect biomass in Germany’s protected areas over 27 years. This equals an average loss of 2.8% of insect biomass each year in areas with low human activity. The study showed a steady decline over nearly three decades.
According to The Economist, this study was the third most cited scientific study in 2017 and led Germany and the Netherlands to create programs to protect insect diversity. Simon Leather, a British entomologist, said media reports about an "ecological Armageddon" may have been exaggerated but stressed the need for more funding for long-term research. He noted that the Krefeld study did not link the decline to climate change or pesticides but suggested intensive farming might be a factor. He also pointed out that the data focused on biomass, not species, and the study sites were not sampled continuously or globally representative.
A 2018 study in Puerto Rico’s El Yunque National Forest found that arthropod biomass dropped by 98% to 78% between 1976 and 2012, along with declines in lizards, frogs, and birds that eat insects. Entomologist David Wagner called the study "a clarion call" and "one of the most disturbing articles" he had read. Researchers linked the decline to rising temperatures, as tropical insects cannot survive large temperature changes. They were surprised by the results, noting that in the 1970s, butterflies were abundant after rain, but in 2012, they were nearly gone.
A 2019 study in the Netherlands found that butterfly numbers dropped by 84% from 1890 to 2017. The decline slowed in grassland and woodland areas but continued in heathland. This was linked to more efficient farming methods that reduced weeds. Recent increases in some populations were attributed to conservation efforts that improved habitat conditions.
A 2019 report by the Swiss Academy of Natural Sciences stated that 60% of studied insects in Switzerland were at risk, mainly in farming and aquatic areas. It also noted a 60% drop in insect-eating birds in rural areas since 1990 and called for urgent action to address the causes.
A 2019 review of 73 long-term insect studies showed an annual 2.5% loss of insect biomass, with some areas experiencing population increases for certain species. The review suggested that 40% of the world’s insect species might go extinct in the next few decades, though this conclusion was challenged. The review faced criticism for focusing on popular insect groups like butterflies, moths, and bees, while underrepresenting other groups such as flies and beetles. It also noted a lack of data from tropical and southern hemisphere regions, where many insects live. Some reviewers questioned the review’s methodology, language, and assumptions about the causes of insect declines.
Impacts
Insect population decline harms ecosystems and other animal populations, including humans. Insects are an important part of many ecosystems around the world. A 2019 global study warned that if this decline is not stopped, it could cause serious problems for the planet's ecosystems. Birds and larger mammals that eat insects may be directly affected by the decline. Fewer insects can reduce the helpful services provided by these insects, such as pollinating crops and breaking down waste.
According to the Zoological Society of London, in addition to the loss of usefulness, the decline also means losing the inherent value of these species.
Countermeasures
The most important problems that can be solved are habitat loss and damage, pesticide use, and climate change. Governments at every level around the world must create policies that effectively address these issues.
Many countries report their efforts to protect biodiversity to the United Nations through the Convention on Biological Diversity. These reports often describe general policies, such as preserving habitats, rather than focusing on protecting specific types of animals or plants. Pollinators, like bees and butterflies, are the main exception, as some countries report actions to help their pollinating insect populations.
After the 2017 Krefeld study and similar research, Germany's environment ministry, the BMU, started an Action Programme for Insect Protection. This program aims to improve insect habitats in farmland, reduce pesticide use, light pollution, and pollutants in soil and water.
In addition to stopping habitat loss and climate change, reducing pesticide use is necessary to protect insect populations. Pesticides have been found far from where they are used. Laws that ban the use of pesticides for non-essential purposes, along with overall reductions in pesticide use, could help insects. Farming methods that avoid pesticides, such as organic farming, may also help.
However, some scientists warn that focusing too much on reducing pesticide use could be harmful. Pests already cause 35% of crop loss, and this could increase to 70% without pesticides. If more land is cleared for farming to replace lost crops, it might worsen insect decline.
A wildflower strip is a section of land planted with a variety of flowering plants that support insects and pollinators. These strips are often placed along the edges of farmland to help protect biodiversity, support insect life, and reduce the harm caused by intensive farming.
Scientists have suggested creating buffer zones around nature reserves where pesticide use is greatly reduced. A study in Germany found that insect samples in these areas often contain about 16 different pesticides, depending on nearby farmland.
The Entomological Society of America recommends that people grow a variety of plants in their gardens and leave natural areas, such as leaf piles and fallen wood. The Xerces Society in the U.S. has organized the Western Monarch Thanksgiving Count for 22 years, where volunteers help track monarch butterfly populations.
It has been suggested that even small changes, like converting 10% of lawns to natural vegetation, could help insects survive and reduce the cost of lawn care.
In 2019, 27 British entomologists and ecologists wrote an open letter to The Guardian, urging scientists to study the causes of insect declines. Notable signers included experts like Simon Leather, Stuart Reynolds, John Krebs, and others. The letter asked for urgent research into how insect declines might harm ecosystems.
More media coverage about insect conservation has been suggested.
In a 2019 study, scientists reviewed 100 studies and other sources showing that insects can help achieve the United Nations' Sustainable Development Goals (SDGs) set in 2015. They argued that policies should shift from viewing insects as pests to seeing them as important for ecosystem services, such as pollination, soil health, and food for other animals. Many people are unaware of the benefits insects provide, and negative views about insects are common.
Society and culture
In April 2019, Carol Ann Duffy shared several poems, including her own and others, to celebrate the end of her time as Britain's poet laureate. This event happened at the same time as protests by the environmental group Extinction Rebellion. The poems were written by Fiona Benson, Imtiaz Dharker, Matthew Hollis, Michael Longley, Daljit Nagra, Alice Oswald, and Denise Riley. Duffy's poem was titled "The Human Bee."
One reason studies about insect decline are limited is that fewer people are studying entomology and taxonomy. At the 2019 Entomology Congress, Jürgen Gross, a leading entomologist, said, "We are ourselves an endangered species." Wolfgang Wägele, an expert in systematic zoology, added, "In universities, we have lost nearly all experts." In 2016, Jürgen Deckert of the Berlin Natural History Museum noted that while about 30,000 insect species live in Central Europe, only a few specialists study them. These specialists often do monitoring as a side job. College biology courses give less attention to insects, and fewer biologists are focusing on entomology as other fields, like genetics, grow. Studies on insect decline often involve trapping and killing insects, which raises concerns for conservationists.
The above information describes the situation in developed countries. In developing countries, entomology has not had time to grow as much. Because of this, most major insect studies have come from Europe and the United States. However, less than 20% of all insect species worldwide live in these regions.