The Decline and Fall of Insects

If all mankind were to disappear, the world would regenerate back to the rich state of equilibrium that existed ten thousand years ago.  If insects were to vanish, the environment would collapse into chaos.
E.O. Wilson

 

In his delightful book about growing up as a budding young naturalist in Britain, where he discovers joy in nature, Michael McCarthy describes nighttime “snowstorms” of moths that sadly no longer swarm in the local meadowlands.  His recollection fits with other amateur reports of diminished populations of fireflies, bees, and butterflies, and the well-known decline of the monarch butterfly population in North America.  A new study from Germany now reports a 75 percent decline in total insect numbers in protected areas during the past few decades.

A few minutes in the evening light on our front porch in Maine would convince nearly everyone that there has been no serious decline in the population of mosquitoes.  But, the various reports of declining numbers in other insect groups suggest that we should watch their population trends worldwide.

What could cause such a decline? I doubt the recent suggestion that insect decline is due to collisions with automobiles on high-speed roadways.  While I have blogged about the environmental impacts of roads—how they fragment and open up natural habitat—I suspect that road death is not involved here. The carnage on windshields can be impressive, but roads cover less than one percent of the landscape, and a car is passing any point on a high-speed roadway only a small fraction of the time.

Loss of available habitat, increased nighttime lighting, and climate change have also been suggested to cause the decline of certain species.  The observation that the insects declined in protected areas suggests that the cause is a widespread and not local factor. My suspicion, albeit without scientific proof, is that insect decline is associated with the use of pesticides on farms, golf courses, and suburban yards, from which pesticide residues escape and circulate in nature where they persist at low concentrations that are lethal to many insects.

I suspect that the average citizen is somewhat nonchalant about the potential demise of insects, despite knowing that insects are the sole pollinators of important fruit and nut crops.  It is worth noting that the decline in insects coincides with a decline in the bird populations in both Europe and North America, with many of the insectivorous bird species being among the hardest hit. Decline in birds may be due to many factors, but the simultaneous decline of insects and birds needs to be examined for cause and effect.

If low levels of insecticides, many of them endocrine disruptors, are involved, humans are certainly exposed as well, with the potential impacts on the occurrence of cancer, developmental disorders, and low sperm counts, as reported widely during the past few decades.

An evening without fireflies is sad. The implications are enormous.

 

References

Cameron, S.A. and 6 others. 2011.  Patterns of widespread decline in North American bumble bees.  Proceedings of the National Academy of Sciences US 108: 662-667.

Dunn, R.R. 2005.  Modern insect extinctions, the neglected majority.  Conservation Biology 19: 1030-1036.

Goulson, D., E. Nicholls, C. Botias and E.L. Rotheray.  2015.  Bee declines driven by combined stress from parasites, pesticides, and lack of flowers.  Science 347: doi: 10.1126/science.1255957

Hallmann C.A. and 11 others.  2017. More than 75 percent decline over 27 years in total flying insect biomass in protected areas. PLoS ONE 12: doi.org/10.1371/journal.pone.018580

McCarthy, M. 2015.  The Moth Snowstorm. Nature and Joy.  New York Review of Books, New York.

Schipper, A. and 19 others. 2016.  Contrasting changes in the abundance and diversity of North American bird assemblages from 1971 to 2010.  Global Change Biology 22: 3948-3959.

Vilela, C.L.S., J.P. Bassin, and R.S. Peixoto. 2018.  Water contamination by endocrine disruptors: Impacts, microbiological aspects and trends for environmental protection.  Environmental Pollution 235: 546-559.

 

One thought on “The Decline and Fall of Insects

  1. Bill – I agree totally that insect populations appear to have drastically declined. I was just discussing this today, before reading your post, with a colleague who raises monarch butterflies, and lamenting the present day lack of grasshoppers and butterflies. I was an avid butterfly collector in my youth, but where I used to collect around my home there are now very few left.

    I would argue that land use change is a major factor here. The lack of butterflies in my home town seems to have resulted from the elimination of suitable plants to feed and reproduce on. When I walk the alleys and roadways where I used to hunt “bugs”, they are now sterile lawns, with few bushes and wider roads. I rarely even here late summer cicadas as I did when young, and which used to fill the late afternoons with such a noise! The field behind my house became the soccer field for the high school. The vast open spaces beyond that are gone. I lived on the edge of town in the 1950s-1960s in Frederick, MD and this city used to be the size of Boone in NC (16,000) but is now the 2nd largest town in MD!. Frederick now extends 5 miles beyond my house, and that land is now composed of parking lots, roads, and lawns, but no open fields. Frederick used to have bazillions (a unit all kids know about!) of fireflies. My dad studied them for the Army, and used to pay everyone $0.01/fly in the summer, and with little effort, we could collect those bazillions in just a few nights. Now, they are much rarer and less abundant. Multiply these habitat losses by all the growing towns in the United States and world, and I think you would have to conclude that loss of habitat must play a major role here.

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