Decline in insect populations

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.

Very occasionally, the record also appears to show mass extinctions of insects, understood to be caused by natural phenomena such as volcanic activity or meteor impact.

Insect diversity has recovered after mass extinctions, as a result of periods in which new species originate with increased frequency, although the recovery can take millions of years.

In a report on the world's invertebrates, the Zoological Society of London suggested in 2012 that insect populations were in decline globally, affecting pollination and food supplies for other animals.

[24][25] Ecologist Dave Goulson told The Guardian in 2017: "We appear to be making vast tracts of land inhospitable to most forms of life, and are currently on course for ecological Armageddon.

[28] In March 2019 Chris D. Thomas and other scientists wrote in response to the apocalyptic "Insectageddon" predictions of Sánchez-Bayo, "we respectfully suggest that accounts of the demise of insects may be slightly exaggerated".

[31] A study placed these causes in the order of importance as follows: "(i) habitat loss and conversion to intensive agriculture and urbanisation; ii) pollution,[32] mainly that by synthetic pesticides and fertilisers; iii) biological factors, including pathogens and introduced species; and iv) climate change.

A 2018 Science Magazine paper estimated that at 1.5 °C (2.7 °F), 2 °C (3.6 °F) and 3.2 °C (5.8 °F), over half of climatically determined geographic range would be lost by 6%, 18% and ~49% of insect species, with this loss corresponding to >20% likelihood of extinction over the next 10–100 years according to the IUCN criteria.

The strongest effects were seen in the southern regions, where rapid increases in frequency of extreme warm years had exceeded the species’ historical temperature ranges.

Estimates for diversity loss at a planetary level tend to involve extrapolating from abundance or biomass data; while studies sometimes show local extirpation of an insect species, actual world wide extinctions are challenging to discern.

[45] The traps are "effectively upside-down Hoovers running 24/7, continually sampling the air for migrating insects", according to James Bell, the survey leader, in an interview in 2017 with the journal Science.

[46] Another anecdote is recalled by environmentalist Michael McCarthy concerning the vanishing of the "moth snowstorms", a relatively common sight in the UK in the 1970s and earlier.

[48][49] In 2013 the Krefeld Entomological Society reported a "huge reduction in the biomass of insects"[4] caught in malaise traps in 63 nature reserves in Germany (57 in Nordrhein-Westfalen, one in Rheinland-Pfalz and one in Brandenburg).

[1][4][52][53][54] Scientists stated in 2019: "In 2017, a 27-year long population monitoring study revealed a shocking 76% decline in flying insect biomass at several of Germany's protected areas (Hallmann et al., 2017).

This represents an average 2.8% loss in insect biomass per year in habitats subject to rather low levels of human disturbance, which could either be undetectable or regarded statistically non-significant if measurements were carried out over shorter time frames.

A 2018 study of the El Yunque National Forest in Puerto Rico reported a decline in arthropods, and in lizards, frogs, and birds (insect-eating species) based on measurements in 1976 and 2012.

They wrote that the review "revealed dramatic rates of decline that may lead to the extinction of 40% of the world's insect species over the next few decades",[6][66] a conclusion that was challenged.

[67][68] They did note the review's limitations, namely that the studies were largely concentrated on popular insect groups (butterflies and moths, bees, dragonflies and beetles); few had been done on groups as Diptera (flies), Orthoptera (which includes grasshoppers and crickets), and Hemiptera (such as aphids); data from the past from which to calculate trends is largely unavailable; and the data that does exist mostly relates to Western Europe and North America, with the tropics and southern hemisphere (major insect habitats) under-represented.

[72][73]The windshield phenomenon – car windscreens covered in dead insects after even a short drive through a rural area in Europe and North America – seems also largely to have disappeared; in the 21st century, drivers find they can go an entire summer without noticing it.

[10][48] John Rawlins, head of invertebrate zoology at the Carnegie Museum of Natural History, speculated in 2006 that more aerodynamic car designs could explain the change.

Declining insect populations can reduce the ecosystem services provided by beneficial bugs, such as pollination of agricultural crops, and biological waste disposal.

[82] The Entomological Society of America suggests that people maintain plant diversity in their gardens and leave "natural habitat, like leaf litter and dead wood".

Signatories included Simon Leather, Stuart Reynolds (former president of the Royal Entomological Society), John Krebs and John Lawton (both former presidents of the Natural Environment Research Council), Paul Brakefield, George McGavin, Michael Hassell, Dave Goulson, Richard Harrington (editor of the Royal Entomological Society's magazine, Antenna), Kathy Willis and Jeremy Thomas.

[84] The letter requested action "to enable intensive investigation of the real threat of ecological disruption caused by insect declines without delay".

[85] In a 2019 paper, scientists listed 100 studies and other references suggesting that insects can help meet the Sustainable Development Goals (SDG) adopted in 2015 by the United Nations.

[86][87] The public in many countries is largely unaware of benefits and services that insects provide (such as honey, ecosystem balance, food for other animals, pollination, soil health, etc.

[77] In April 2019, in response to the studies about insect decline, Carol Ann Duffy released several poems, by herself and others, to mark the end of her tenure as Britain's poet laureate and to coincide with protests that month by the environmentalist movement Extinction Rebellion.

The poets included Fiona Benson, Imtiaz Dharker, Matthew Hollis, Michael Longley, Daljit Nagra, Alice Oswald, and Denise Riley.

[92] In 2016, Jürgen Deckert of Berlin Natural History Museum commented that while around 30,000 insect species are known to inhabit Central Europe, there are "only a few specialists" dedicated to the region, and even they often do monitoring as a side job.

[5] General biology courses in college give less attention to insects, and the number of biologists specialising in entomology is decreasing as specialities such as genetics expand.