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In the 21st century, there appears to be a widespread decline in the number of insects. About 40% of species are threatened by extinction and the types most affected include ants, bees, butterflies, moths and wasps. While some species such as flies and cockroaches might increase as a result, the total biomass of insects is decreasing by about 2.5% per year. The phenomenon is due to multiple factors including habitat destruction, pesticides, introduced species and climate change.

Reviews and studies

In 2012, the Zoological Society of London produced a survey of the prospects of the world's invertebrates: Spineless. It estimated that about 20% of all species were threatened with extinction and that species with the least mobility and smallest ranges were the most at risk.

A comparison of the amount of arthropods in the El Yunque National Forest showed a large decline from 1976 to 2012. Depending on the method of collection, the declines ranged from a factor of 4 to 60. A corresponding decline in the number of insect-eating species such as birds, frogs and lizards was also observed. The decline was attributed to a rise in the average temperature as tropical insect species cannot tolerate a wide range of temperatures.

A 2014 review in Science – Defaunation in the Anthropocene – found that "Of all insects with IUCN-documented population trends, 33% are declining ... Globally, a compiled index of all invertebrate population declines over the past 40 years shows an overall 45% decline".

In 2016, the Entomologischer Verein Krefeld produced a report from their long-term records of insect collections in nature reserves in Germany. This showed that, in the period 1990 to 2016, there had been a decline of 75% in the amount of flying insects.

In 2019, a systematic review of the issue – Worldwide decline of the entomofauna – was published in the journal Biological Conservation. This analysed 73 reports and studies and found that, overall, there were "dramatic rates of decline".

From our compilation of published scientific reports, we estimate the current proportion of insect species in decline (41%) to be twice as high as that of vertebrates, and the pace of local species extinction (10%) eight times higher, confirming previous findings (Dirzo et al., 2014). At present, about a third of all insect species are threatened with extinction in the countries studied (Table 1). Moreover, every year about 1% of all insect species are added to the list, with such biodiversity declines resulting in an annual 2.5% loss of biomass worldwide (Fig. 2).

— Francisco Sánchez-Bayo, Kris Wyckhuys, "Worldwide decline of the entomofauna", Biological Conservation (2019)

Responses

A March 2019 statement by the Entomological Society of America said there is not yet sufficient data to predict an imminent mass extinction of insects. They did though agree that the various studies finding declines are "very concerning".

Conservation measures

Following the 2016 report of the Entomologischer Verein Krefeld and other studies, the German environment ministry – the BMU – started its Action Program for Insect Protection (Aktionsprogramm Insektenschutz). This initially contained nine goals:

1. "Promote insect habitats and structural diversity in the agricultural landscape"
2. "Restore and connect habitats for insects in other landscape areas"
3. "Strengthen protected areas as habitats for insects"
4. "Reduce the use of pesticides"
5. "Reduce inputs of nutrients and pollutants in soil and water"
6. "Reduce light pollution"
7. "Deepening research - multiplying knowledge - closing gaps"
8. "Improve funding - create incentives"
9. "Promote the commitment of society"

The Entomological Society of America advise that measures regular people can take include maintaining plant diversity in their gardens, and leaving "natural habitat, like leaf litter and dead wood."

Citizen science is used to monitor insect populations. People have noticed a decline in the number of insects splattered on car windshields when they drive across their country – the windshield phenomenon. Phone apps such as iNaturalist can be used to photograph and identify specimens and these are being used in programs such as the City Nature Challenge. Activities and projects may focus upon a particular type of insect such as National Moth Week and monarch butterfly conservation in California.

See also

• Biodiversity decline
• Colony collapse disorder
• Decline in amphibian populations
• Holocene extinction
• Pollinator decline

References

1. ^ Hallmann, CA; Sorg, M; Jongejans, E; Siepel, H; Hofland, N; Schwan, H (18 October 2017), "More than 75 percent decline over 27 years in total flying insect biomass in protected areas", PLoS ONE, 12 (10), doi:10.1371/journal.pone.0185809{{citation}}: CS1 maint: unflagged free DOI (link)
2. McGrath, Matt (11 February 2019), Global insect decline may see 'plague of pests', BBC {{citation}}: Cite has empty unknown parameter: |1= (help)
3. ^ Sánchez-Bayo, Francisco; Wyckhuys, Kris A.G. (31 January 2019), "Worldwide decline of the entomofauna: A review of its drivers", Biological Conservation, 232: 8–27, doi:10.1016/j.biocon.2019.01.020
4. ^ Damian Carrington (10 February 2019), "Plummeting insect numbers 'threaten collapse of nature'", The Observer
5. Vogel, Gretchen (10 May 2017), "Where have all the insects gone?", Science
6. Collen, Ben; Böhm, Monika; Kemp, Rachael; Baillie, Jonathan E. M., eds. (2012), Spineless – Status and trends of the world's invertebrates (PDF), Zoological Society of London, ISBN 978-0-900881-70-1
7. Borrell, Brendan (4 September 2012), "One Fifth of Invertebrate Species at Risk of Extinction", Scientific American {{citation}}: Cite has empty unknown parameter: |1= (help)
8. Lister, Bradford C.; Garcia, Andres (October 2018), "Climate-driven declines in arthropod abundance restructure a rainforest food web", Proceedings of the National Academy of Sciences, 115 (44), doi:10.1073/pnas.1722477115
9. Guarino, Ben (15 October 2018), "'Hyperalarming' study shows massive insect loss", The Washington Post {{citation}}: Cite has empty unknown parameter: |1= (help)
10. Jarvis, Brooke (27 November 2018), "The Insect Apocalypse Is Here", The New York Times
11. Dirzo, Rodolfo; Young, Hillary; Galetti, Mauro; Ceballos, Gerardo; Isaac, Nick; Collen, Ben (25 July 2014), "Defaunation in the Anthropocene" (PDF), Science, 345 (6195): 401–406, doi:10.1126/science.1251817
12. McGrane, Sally (4 December 2017), "The German Amateurs Who Discovered 'Insect Armageddon'", The New York Times {{citation}}: Cite has empty unknown parameter: |1= (help)
13. ^ Global Insect Biodiversity:Frequently Asked Questions (PDF), Entomological Society of America, March 2019 {{citation}}: Cite has empty unknown parameter: |1= (help)
14. Bélanger, J.; Pilling, D., eds. (2019), The State of the World’s Biodiversity for Food and Agriculture (PDF), Rome: FAO Commission on Genetic Resources for Food and Agriculture, p. 133
15. Action program insect protection (in German), Bundesministerium für Umwelt, Naturschutz und nukleare Sicherheit, 10 October 2018
16. Katherine Roth, Apps let everyone help track health of insect populations, Associated Press {{citation}}: Text "15 January 2019" ignored (help)

• Environmental conservation
• Extinct insects
• Population ecology
• Insects
• Extinct invertebrates since 1500