Decline in insect populations

Insects are the most numerous and widespread class in the animal kingdom, accounting for up to 90% of all animal species.^[2][3] In the 2010s, reports emerged about the widespread decline in insect populations across multiple insect orders. The reported severity shocked many observers, even though there had been earlier findings of pollinator decline. There has also been anecdotal reports of greater insect abundance earlier in the 20th century. Many car drivers know this anecdotal evidence through the windscreen phenomenon, for example.^[4][5] Causes for the decline in insect population are similar to those driving other biodiversity loss. They include habitat destruction, such as intensive agriculture, the use of pesticides (particularly insecticides), introduced species, and – to a lesser degree and only for some regions – the effects of climate change.^[6] An additional cause that may be specific to insects is light pollution (research in that area is ongoing).^[7][8][9]

Most commonly, the declines involve reductions in abundance, though in some cases entire species are going extinct. The declines are far from uniform. In some localities, there have been reports of increases in overall insect population, and some types of insects appear to be increasing in abundance across the world.^[10] Not all insect orders are affected in the same way; most affected are bees, butterflies, moths, beetles, dragonflies and damselflies. Many of the remaining insect groups have received less research to date. Also, comparative figures from earlier decades are often not available.^[10] In the few major global studies, estimates of the total number of insect species at risk of extinction range between 10% and 40%,^{[11][6][12][13]} though all of these estimates have been fraught with controversy.^{[14][15][16][17]}

Studies concur that in areas where insects are declining, their abundance had been diminishing for decades. Yet, those trends had not been spotted earlier, as there has historically been much less interest in studying insects in comparison to mammals, birds and other vertebrates. One reason is the comparative lack of charismatic species of insects. In 2016, it was observed that while 30,000 insect species are known to inhabit Central Europe, there are practically no specialists in the region devoted to full-time monitoring.^[4] This issue of insufficient research is even more acute in the developing countries. As of 2021, nearly all of the studies on regional insect population trends come from Europe and the United States, even though they account for less than 20% of insect species worldwide. In Africa, Asia and South America there are hardly any observations of insects that span several decades. Such studies would be required to draw conclusions about population trends on a large scale.^[18]

To respond to these declines, various governments have introduced conservation measures to help insects. For example, the German government started an Action Programme for Insect Protection in 2018.^[19][20] The goals of this program include promoting insect habitats in the agricultural landscape, and reducing pesticide use, light pollution, and pollutants in soil and water.^[20]