Insects and Climate Change

The evidence is clear that the earth is slowly getting warmer. The warming is mostly due to the increase in “greenhouse effect” gasses that trap heat from the sun. The interior of your car will heat up in the sun because the glass admits short wavelength light. When the light hits the surfaces inside the car, energy from the light is absorbed by the surfaces inside the car. Some of the energy is reflected as longer wavelength (and invisible to our eyes) infrared radiation. However glass does not permit the infrared radiation to escape. Instead, the glass reflects the infrared radiation and it is absorbed, causing the surfaces in interior of the car to become warmer than surfaces outside the car.

In our atmosphere, carbon dioxide will reflect and trap infrared (heat) radiation more efficiently than other atmospheric gasses. As the concentration of carbon dioxide in our atmosphere increases from burning fossil fuels, the earth warms. The warming is a slow process. It takes years for the average temperature to change by less than 1 degree centigrade. The changes are most noticeable in cold areas with a lot of ice. As the temperature warms, there is a reduction in the ice and that causes subtle and eventually drastic changes in the environment.

The effects of climate change on our environment are not predictable, but they can be documented with careful study. Mayflies are often used as indicators of environmental quality. The larvae live in water and are affected by changes in water quality such as pollution, oxygen content and water temperature.

James Owen, in National Geographic, discusses studies of mayflies that show subtle effects of global warming. One study by Nick Everall (not yet published) of the mayfly, Ephemera danica, is found that the average water temperature has increased by about 1 degree centigrade an average summer temperature increased by 2 degrees centigrade over the past 20 years. These subtle changes may contribute to significant changes in the biology of the mayfly.

The body temperature of an insect is dependent on the temperature of the surrounding environment. At higher temperatures, insects are somewhat warmer (most insects have some, but often limited, ability to regulate temperature). At warmer temperatures, growth and development is faster. The small changes in water temperature have led to faster development rates of Ephemera danica. Faster development can be due to a combination of faster metabolism, more feeding, or differences in food quality and availability at the higher temperature. In 2007, most of the Ephemera danica, spent 2 years underwater feeding as larvae. By 2011, most of the Ephemera danica, have switched to a 1 year larval period.

The adults that emerge after one year are 8 to 10 mm shorter than the typical 2 year mayflies. The smaller size was first noted by fishermen who tie flies to imitate the mayflies. The reports by the fishermen triggered the investigation. How can the change in size be confirmed? Mayflies collected years ago and kept in insect museum collections can be compared to the mayflies collected today. Research collections allow these types of comparisons to be made.


The smaller mayfly adults lay fewer eggs. A one year life cycle means less buffering against a bad year when weather adversely affects egg laying. The change in water temperature make Ephemera danica less well adapted to local conditions. Will they evolve new adaptations to the warmer temperatures? Or will they go locally extinct to be replaced by other mayflies (or not)? While we can document the effects of global warming, the eventual outcomes are uncertain and unpredictable. Increasing global temperatures have led to calls to limit the amount of carbon dioxide released into our atmosphere and keep the rate of climate change as slow as possible so that humans and other species have more time to adapt to the effects of the changes.

About jjneal

Jonathan Neal is a retired Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
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2 Responses to Insects and Climate Change

  1. Janice says:

    I am a reporter working on a story about the correlation of insect populations and climate change. I am focusing on the High Country of Colorado, where I work and write for the Summit Daily News. At 9,000 feet, we typically don’t see many mosquitoes or ticks, but I’ve heard it said that warming temperatures may start bringing them and other insects into this upper elevation territory. Would you be able to provide any input for this story, Mr. Neal?

    • jjneal says:

      The distribution of mosquitoes and diseases depend on many factors other than climate. For example, in 1882, malaria was prevalent in all the area of the US between the Appalachian mountains and the Rockies, including Eastern Colorado. Malaria was eliminated from these areas by 1) draining the swamps and eliminating mosquito breeding sites, 2) the use of window screens. These two steps eliminated malaria from almost all of the US between the 1880s and 1940. The last persistent pockets of malaria in the US were eliminated by DDT treatments shortly after WWII.

      The mosquitoes that can transmit malaria were not eliminated, but once the prevalence of malaria drops to a low level, the transmission rate becomes very low an the disease becomes rare.

      As for mosquitoes in the Colorado Rockies: Most mosquito species require slow moving water to breed. One reason for low populations of mosquitoes in the Colorado Rockies is low moisture, lack of standing water. Climate change can affect precipitation and that would be more likely to contribute to changes in the ranges of mosquitoes than temperature. Some of the highest mosquito population densities occur in the Arctic, which during much of the year is colder than Colorado at 9000 feet. The Arctic has more moisture than the Eastern slope of the Rockies.

      Climate is complex, which makes changes from greenhouse gasses difficult to predict for specific locations. Climate change will produce more extreme weather events in all areas. Ecosystems are even more complex and interact with climate. Few ecosystems are understood in a level of detail that predictions based on climate can be made. Where temperature is a barrier, then warming can extend the ranges of some species northward or to higher elevations. However, temperature is not always the barrier. The barrier may be precipitation or humidity or other abiotic factor or the barrier can be biological. Diseases, parasitoids, predators, key hosts, can all affect distribution of a species. It would be a mistake to generalize about future mosquito populations in Summit county or any other county given the current state of knowledge.

      That said, there are some species that have temperature as a key factor, including Mountain Pine Beetle which has expanded its range as the climate has warmed. The millions of dead pines are fuel for the forest fires current and present a fire hazard going forward.

      In short, mosquito range expansion is not temperature dependent. Moisture is a more important factor.
      For some species such as MPB, higher temperatures (especially because low winter temperatures kill beetles) is a key factor. Every species must be evaluated based on its own key limiting factors.

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