The presence behind this name can hardly be missed.
| Photo Credit: Wikimedia Commons

You are standing in a forest in the middle of winter and the temperature has dropped below zero. The ground is covered in snow and the trees and bushes are naked. The insects that normally fly or crawl in warmer weather are nowhere to be seen.

You might assume that insects do not survive the seasonal shift. After all, temperatures are too low for them to forage and the plants or other insects they’d eat are scarce anyway.

But that is not the case. Actually, they are still all around you: in the bark of the trees and bushes, in the soil, and some may even be attached to plants underneath the snow. Snow, as it turns out, is a rather good insulator – almost like a blanket.

The insects are hibernating. Scientists call this a “diapause” and it is how insects, which in most cases cannot generate their own heat like we mammals can, survive the cold winter months.

Winter is coming…

Insects have to prepare for winter before the temperature gets too low. For some species, hibernation is a part of life. These species have one generation a year, and every individual will experience winter and hibernate no matter the conditions.

However, most insects only get the cue to hibernate from their environment. This allows a species to have several generations a year in which only one experiences winter. Those species must somehow foresee winter’s approach.

So how do they do it? Temperature is not a particularly reliable signal. Although temperatures get colder towards winter, they can vary a lot from week to week. Another environmental factor can be trusted to be the same every year: day length.

A great variety of insects interpret the shortening days as their cue to prepare for hibernation, unless there is still time for another generation before winter descends. Take the speckled wood butterfly. This butterfly can sense the lengths of days as a larva (it is still not fully known how) and if they are suitably short, it gains extra weight and, as a pupa (or chrysalis), hibernates.

Correctly assessing when winter will arrive is crucial for survival. If an insect fails to make the right decision on time it may freeze or starve, or spend all of its hard earned energy before it can safely emerge from hibernation.

A long winter’s gnat

Hibernation entails several strategies that have allowed this vast class of animals, comprising approximately 5.5 million species, to cope with the cold far from Earth’s balmy equator.

Some insects hibernate in places that conceal them from low temperatures while others undergo changes within their bodies to either avoid or tolerate freezing. Our friend the speckled wood butterfly, after gaining weight as a larva, will search for a suitably sheltered spot to bed down in its forest habitat – perhaps on the grass (which it eats the rest of the year) that will become covered in 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: gain additional weight before winter and consume this energy store slowly by lowering their metabolic rate.

Many insects live their entire life cycle (from egg to larva, pupa and adult) within a few months to a year. Losing months during winter is significant. And so, insects simply pause their development during hibernation. Which life stage species hibernate in differs from species to species. But the speckled wood butterfly, found across Europe and North Africa, turns into a pupa just before winter and develops into a butterfly several months later in spring.

Change is in the air

Rising global temperatures caused by burning fossil fuels, animal agriculture and deforestation, among other things, have resulted in shorter and warmer winters.

For insects that can adapt to these changes fast enough, it leaves an opportunity to expand northwards and produce more generations per year where they currently are. Some species have managed to do this while others can’t – entomologists are expending great effort to understand why.

The challenges of adapting to warmer winters are manifold. Temperatures drop later and later in the season, but days shorten as consistently as they ever did. This mismatch can trick insects into making the wrong decision. If this happens to too many insects, a species can go locally extinct.

Studies suggest that some insects can change the day length they use to diagnose winter’s approach relatively quickly. However, it is not known if all species will be so capable.

Energy consumption in insects is also temperature-dependent. As winters warm, an insect risks depleting its energy stores before it can terminate hibernation.

Higher temperatures during winter also mean less snow, which, somewhat ironically, means that some species cannot conceal themselves from the cold.

Expanding northwards can be a somewhat limited opportunity. The food source or habitat an insect relies on may not be available in its new home, especially if the species live offs just a few plants or its habitat is not found further north.

With more research into the factors influencing how different insects adapt to higher temperatures during winter, scientists could predict which species will need more urgent help from conservationists – and what form that help should take.

Next time you are standing in a forest on a cold winter day, think about how amazing it is that hibernating insects are surviving, for several months at a time, in a climate where they would otherwise perish.

(Author: Anna Brødsgaard Shoshan, PhD Candidate, Zoology Department, Stockholm University)

(Disclosure Statement:  Anna Brødsgaard Shoshan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment)

This article is republished from The Conversation under a Creative Commons license. Read the original article.
 

(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)

The European Space Agency (ESA) on Saturday released a satellite picture of day and night split in half on Earth’s surface. The image posted on X, formerly Twitter, shows the crossing of the Sun in the celestial equator in the sky and bringing autumn to the Northern Hemisphere. Sharing the picture, the space agency wrote, “Winter is coming. Day and night are split in half today, as the Sun crossed the celestial equator in the sky at 07:50 BST/08:50 CEST marking the autumn equinox in the Northern Hemisphere. This #Meteosat image was taken at 09:00 BST/10:00 CEST this morning.”

Winter is coming

Day and night are split in half today, as the Sun crossed the celestial equator in the sky at 07:50 BST/08:50 CEST marking the autumn equinox in the Northern Hemisphere.

This #Meteosat image was taken at 09:00 BST/10:00 CEST this morning (pic: EUMETSAT) pic.twitter.com/t7oUI36ai4

— ESA (@esa) September 23, 2023

Since being shared, the post has amassed a lot of reactions from social media users.

“This is an interesting post !” said a user.

“Incredible,” said another person.

“The autumn equinox has begun in the Northern Hemisphere. Shown here, a grand image of Earth from Meteosat in space with Africa, Europe, and the Middle East positioned to the front,” commented another user.

A person added, “Amazing; I had no idea the countries of the world were drawn onto the Earth like that.”

As per Space.com, Autumn began astronomically in the Northern Hemisphere and spring started in the Southern Hemisphere. “The sun is currently migrating south, having spent the previous six months shining directly on the northern half of our planet. So, at the official start time of autumn, the sun would appear directly overhead from a ship in the Laccadive Sea, positioned on the equator, 170 miles (275 kilometres) northeast of Addu City in the Maldives,” the website said. 

The Earth’s axis is tilted either towards or away from the sun for the majority of the year. It follows that the planet’s northern and southern portions receive different amounts of warmth and light from the sun. The Earth’s axis and orbit align at the equinox, distributing sunlight equally to both hemispheres.

Two Latin words that signify equal and night make up the word equinox. This is due to the fact that on the equinox, day and night are almost equal in length. However, depending on where you are on the planet, one may get a few some extra minutes.