Scientists found a bug that generates its own heat in freezing cold
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Scientists found a bug that generates its own heat in freezing cold
Snow flies survive freezing by making their own heat and blocking ice.
Date:
March 26, 2026
Source:
Northwestern University
Summary:
Snow flies have an unexpected way of surviving freezing temperatures. They produce antifreeze proteins to block ice formation and can even generate their own heat. Scientists also found that their genes are unusually unique, and they feel less cold-related pain than other insects. These combined traits let them stay active in conditions that would freeze most species.
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New research finds the snow fly (Chionea alexandriana) counteracts subzero temperatures by creating bursts of body heat and producing antifreeze proteins. Credit: Håkan Söderholm
Snow flies might seem like ordinary insects, but their survival strategy is anything but typical.
In a new study, scientists at Northwestern University investigated how these small, wingless insects, which move across snowy surfaces to find mates and lay eggs, stay alive in freezing conditions. They discovered that snow flies rely on a surprising mix of biological tools. The insects can generate their own body heat like mammals and produce antifreeze proteins similar to those found in Arctic fish.
While most insects cannot survive below freezing, snow flies remain active at temperatures as low as -6 degrees Celsius (or 21.2 degrees Fahrenheit).
These findings provide new insight into how life adapts to extreme environments. They may also help researchers develop new ways to protect cells, tissues and materials from damage caused by cold.
The study was published on March 24 in the journal Current Biology.
"Insects are cold-blooded, so they are at the mercy of external temperatures," said Northwestern's Marco Gallio, who led the study. "But they have a mind-boggling ability to adapt to extremes. When it gets cold, a common strategy is to find shelter and become dormant until conditions get better. But instead of slowing down, snow flies actually prefer freezing cold, snowy conditions and hide away when the snow melts and it gets warm. They really push the limit of what's possible. Now we've found snow flies aren't just tolerating the cold, they have multiple ways to counteract it."
Gallio studies how temperature shapes biology and is the Soretta and Henry Shapiro Research Professor in Molecular Biology as well as a professor of neurobiology at Northwestern's Weinberg College of Arts and Sciences. He co-led the study with Marcus Stensmyr, a biology professor at Lund University in Sweden. Other Northwestern contributors include William Kath of the McCormick School of Engineering and Alessia Para from Weinberg. Gallio and Kath are also affiliated with the NSF-Simons National Institute for Theory and Mathematics in Biology (NITMB).
Unusual Genes and Antifreeze Proteins
To understand how snow flies survive such harsh conditions, researchers first examined their genetic makeup. Gallio and his team were the first to sequence the snow fly genome and compare it with related insects that are not adapted to cold environments. They also analyzed RNA to identify which genes are actively used for survival in freezing temperatures. These complex comparisons were carried out by Richard Suhendra, a Ph.D. student working with Kath.
The results were unexpected.
"We couldn't find many of the genes within any database," Gallio said. "Initially, I thought we must have sequenced some alien species. It's very rare for an active gene, which makes a protein, to not have a match."
Further investigation showed that these unusual genes produce antifreeze proteins. Like those found in Arctic fish, these proteins attach to ice crystals and prevent them from growing. This process protects cells from damage during freezing.
"Remarkably, some of the antifreeze proteins we found are actually structurally related to those of Arctic fish," Gallio said. "That suggests evolution came to the same solution for a common problem."
Heat Production Helps Snow Flies Stay Active
The team also identified genes linked to energy use and cellular processes involved in producing heat. This suggested another unexpected ability. Snow flies do not just resist freezing, they also generate their own heat.
"We found genes that in larger animals are associated with mitochondrial thermogenesis in brown adipose tissue," Gallio said. "Many animals like marmots and polar bears have brown fat, which is there to produce heat. When they go into hibernation, they burn this stored fat to produce heat rather than to produce chemical energy. So, in some ways snow flies use a combination of the strategies used by polar bears and by Arctic fish."
Blocking Ice and Creating Warmth
To test how the antifreeze proteins work, Matthew Capek, a Ph.D. student in the Gallio Lab, modified fruit flies to produce one of th