A common misconception is that arthropod life simply dies off in the colder months. In reality, we know that arthropod life survives in some capacity all year round thanks to a pretty cool list of ways that they can survive sub-freezing temperatures. Many organisms can produce antifreeze-like substances that prevent their cells from freezing, while others may use various methos of cold avoidance such as finding a warm place to hide to wait out the winter months. A lot of arthropods may use a combination of both strategies, antifreeze-like stuff to keep their bodies from freezing while seeking protection from harsh conditions under leaflitter or even under the snow itself.

Surprisingly, snow can act as an excellent insulator and provide a blanket of protection underneath. Specifically, when the snowpack reaches about 15-20cm, it can create a stable environment below that can remain warmer than ambient air temperatures exposed to freezing winds and other conditions. This protective region is known as the subnivium and can serve as a winter refuge for a long list of organisms.

While it’s known that life does survive in the subnivium, there are a lot of questions surrounding the diversity and abundance of arthropods that can be found in this insulated zone. To address this gap in knowledge, a group of researchers at the University of New Hampshire surveyed arthropod communities in a remote forested area using pitfall traps. They collected samples over two summers and one winter to compare what they found across seasons.

In total, over 20,000 arthropods were collected including various species of collembola, mites, spiders, beetles, millipedes, and centipedes. Collembola and mites were the first and second most trapped arthropods. Not surprisingly, samples collected during the summer months accounted for approximately 6-fold more arthropods than winter collections. The researchers also reported that insects accounted for roughly 18% of collection in winter and 25% in summer months. And, that about 95% of everything collected were adults.

 

As predicted, communities in winter months tended to be lower in most measures of abundance and diversity compared to the summer collections. Specifically, the subnivium community was much lower in overall abundance as well as biomass. In other words, the range of different species and the overall total number of bugs they caught in the winter months was lower than the summer months. What was really interesting was that some arthropods were dominant in the subnivium but rare or absent in the summer collections. About 37% of species were exclusively recovered in the winter, with rove beetles and spiders being the most prominent insects recovered in the winter samples (~26.6%).

 

This paper aligns with other past studies demonstrating that life simply doesn’t pause during the winter months. There are a wide range of diverse and distinct communities of arthropods that have evolved as specialists to not only survive but THRIVE in subfreezing temperatures under snowpack. This research also shows that, while the arthropods recovered in this study may not be high on the structural pest control’s most wanted list, heavy snowfall doesn’t equate to a decline in arthropod populations. And one could argue that heavy snowfall would even help to protect some arthropod communities (like ticks) by providing a thicker layer of insulation that shelters them from subfreezing air temperatures.  

It is important to point out that the way in which samples were collected does inherently have some level of trap-bias that affects what would be recovered. By that I mean a pitfall trap may not be the best way to survey for ticks or other organisms that we know to be active and capable of surviving the winter months. Having said that, this was a really cool study that added to our knowledge and understanding of what these winter communities may look like across seasons.

Article by Mike Bentley, PhD, BCE

References

Christopher P Ziadeh, Shayleigh B Ziadeh, Breanne H Aflague, Mark A Townley, Matthew P Ayres, Alexandra R Contosta, Jeff R Garnas, Distinct communities under the snow: describing characteristics of subnivium arthropod communities, Environmental Entomology, 2024;, nvae017, https://doi.org/10.1093/ee/nvae017

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