You are standing in a forest in the middle of winter and the temperature has dropped below zero. The ground is covered with snow and the trees and bushes are naked. Generally, flying or crawling insects are nowhere to be seen in hot weather.
You might assume that insects do not survive seasonal changes. After all, the temperatures are too low for them to forage and the plants or other insects they will eat are scarce anyway.
But that is not the case. Indeed, they are still all around you: in the bark of trees and bushes, in the soil, and some may even be attached to plants under the snow. Ice, as it turns out, is a good insulator – almost like a blanket.
Insects are hibernating. Scientists call this “diapause” and it’s how insects, which in most cases can’t generate their own heat like we can mammals, survive the cold winter months.
Winter is coming…
Insects have to prepare for winter before temperatures drop too low. For some species, hibernation is a part of life. These species have one generation a year, and each individual will experience winter no matter what the conditions.
However, most insects receive the cue to hibernate only from their environment. This allows a species to produce multiple generations in a year with only one experiencing winter. Those species must somehow herald the arrival of winter.
So how do they do it? Temperature is not a particularly reliable indicator. Although temperatures tend to be cooler in winter, they can vary greatly from week to week. Another environmental factor that can be relied upon is the same every year: day length.
A huge variety of insects interpret the shortening of the days to prepare for hibernation, until there is still time for a second generation before winter arrives. Take the spotted wood butterfly. This butterfly can sense the length of days as a larva (it is still not completely known how) and if they are suitably short, it gains extra weight and, as a pupa (or chrysalis), In form, hibernates.
Correctly estimating when winter will arrive is vital to survival. If an insect fails to make the right decision in time it may freeze or starve to death, or spend all its hard-earned energy before it can safely emerge from hibernation.
the worm of a long winter
Hibernation involves several strategies that have allowed this vast class of animals, which includes about 5.5 million species, to cope with the cold far from Earth’s cool equator.
Some insects hibernate in places that hide them from low temperatures, while others undergo changes within their bodies to avoid or tolerate the cold. Our friend the spotted wood butterfly, after gaining weight as a larva, will look for a suitable sheltered place to stay in its forest habitat – perhaps on grass (which it eats the rest of the year) that will be covered with snow.
There is almost no food available at this time of year and insects generally do not eat during their hibernation. Winter can last for months, so insects have evolved two strategies: gaining extra weight before winter and slowly consuming these energy reserves by reducing their metabolic rate.
Many insects go through their entire life cycle (egg to larva, pupa and adult) within a few months to a year. The shortening of the months during winter is significant. And so, insects simply stop their development during hibernation. The life stage at which species hibernate varies between species. But the spotted wood butterfly, found throughout Europe and North Africa, pupates just before winter and develops into a butterfly several months later in the spring.
Change is in the air
Winters have become shorter and warmer due to rising global temperatures caused by fossil fuel burning, animal agriculture, and deforestation, among other things.
For insects that can adapt to these changes quickly, this leaves an opportunity to expand northward and produce more generations per year where they currently are. Some species have managed to do this while others have not – entomologists are putting a lot of effort into understanding why.
The challenges of adapting to warmer winters are manifold. Temperatures drop from time to time throughout the season, but the days continue to get shorter as never before. This mismatch may lead insects to make wrong decisions. If this happens to too many insects, a species may become locally extinct.
Studies show that some insects can relatively quickly change the length of the day which they use to diagnose the approach of winter. However, it is not known whether all species will be so capable.
Energy consumption in insects also depends on temperature. As winters get warmer, an insect risks depleting its energy reserves before it can end hibernation.
Higher temperatures during winter also mean less snowfall, which, somewhat ironically, means some species cannot hide themselves from the cold.
Expanding northward may be a somewhat limited opportunity. The food sources or habitat that an insect depends on may not be available in its new home, especially if the species depends on only a few plants or its habitat is not found further north.
With more research on the factors that influence how different insects adapt to higher temperatures during the winter, scientists can predict which species will need more immediate help from conservationists – and in what form that help will take. There should be.
The next time you’re standing in a forest on a cold day, think how amazing it is that hibernating insects can survive for months at a time in an environment where they would otherwise perish.
,Author: Anna Brodsgaard Shoshan, PhD Candidate, Department of Zoology, Stockholm University)
,disclosure statement: Anna Brodsgaard Shoshan does not work for, consult, hold shares in, or receive funding from any company or organization that would benefit from this article, and she has no relevant affiliations beyond her academic appointment. not disclosed)
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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