Snow Flies Survive Freezing Temperatures Using Mammal-Like Heat and Fish-Like Antifreeze

When the snow falls, most insects disappear. Snow flies come out. They crawl on the surface in subzero temperatures, remaining active in conditions that would shut down almost everything else.

They rely on an unusual combination of strategies to stay active: antifreeze proteins that prevent ice from spreading through their bodies and the ability to generate small amounts of heat from within – a mix of traits more commonly associated with Arctic fish and warm-blooded mammals than with insects. The results were published in Current biology.

“Insects are cold-blooded, so they are at the mercy of outside temperatures,” study leader Marco Gallio said in a press release. “But they have an astonishing ability to adapt to extremes.

Learn more: These fruit flies age faster after seeing death

How Snow Flies Stay Active Below Zero

To understand how snow flies deal with this, the researchers first looked at their genetic makeup, essentially mapping the biological tools that allow them to function in extreme cold.

Many of the genes that flies rely on don’t match anything in existing databases, suggesting that these insects use adaptations still largely unknown to science.

“We couldn’t find many genes in any database,” Gallio said. “Originally, I thought we must have sequenced some exotic species. It’s very rare that an active gene, which makes a protein, doesn’t match.”

Ultimately, the team identified the genes responsible for producing antifreeze proteins. These proteins bind to ice crystals and prevent them from growing, protecting cells from freezing damage. Similar proteins exist in Arctic fish, showing that very different organisms can find comparable solutions to survive the cold.

To confirm how these proteins worked, the researchers engineered fruit flies to produce one of the proteins and then exposed them to freezing temperatures. The modified flies were much more likely to survive, demonstrating that the protein acts as a microscopic ice blocker, preventing the spread of frost.

A built-in way to generate heat

In addition to antifreeze proteins, researchers found that snow flies can also generate heat internally, a rare ability among insects.

Genetic data has revealed processes similar to those used by mammals to produce heat. In animals like bears and marmots, specialized tissues burn energy to generate heat rather than store it. Snow flies appear to use a comparable strategy, but on a much smaller scale.

To test this, the researchers measured the insects’ internal temperatures while lowering the environment below freezing. The snow flies always remained slightly warmer than expected – a few degrees compared to other insects exposed to the same conditions.

“Other insects, like bees and moths, shiver to increase their heat,” co-author Marcus Stensmyr said in a press release. “But we found no evidence of shivering.”

Instead, heat appears to be generated at the cellular level. Even a slight increase in temperature can slow or prevent freezing, giving insects more time to move or seek shelter as conditions change.

Designed to operate in cold weather

Snow flies are not only resistant to frost, but they also seem to be less susceptible to the damage that cold weather can cause.

In most animals, exposure to extreme cold triggers a strong sensory response that prompts them to move away. This response is driven by receptors that detect harmful conditions. In snow flies, one of these key receptors is much less sensitive than in other insects.

“It turns out that a specific irritant receptor is 30 times less sensitive in snow flies than in mosquitoes and fruit flies,” Gallio said.

This reduced sensitivity allows them to tolerate conditions that would overwhelm most species, allowing them to continue to move and function even if temperatures drop.

Together, these adaptations—antifreeze proteins, internal heat production, and reduced sensitivity to cold—allow snow flies to remain active at temperatures as low as 21.2° Fahrenheit (-6° Celsius).

Learn more: Drunk fruit flies are more successful at mating than their sober counterparts

Article sources

Our Discovermagazine.com editors use peer-reviewed research and high-quality sources for our articles, and our editors review the articles for scientific accuracy and editorial standards. See the sources used below for this article: