WOOLLIES AND CLIMATE CHANGE

As you may have noticed, The Caterpillar Lab has been hard at work this winter! We haven’t shared out about this yet, but one of our major projects has involved reading about the potential effects of climate change on caterpillars. Here, we present our first-ever snippet of caterpillar-specific climate change education!

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NOTE 1: This post has to do with another recent post, WOOLLIES IN WINTER. If you haven’t read that one yet, you might want to do so before you read this.

NOTE 2: Information in this post comes from two journal articles by Katie Marshall and Brent Sinclair of The University of Western Ontario. Please look up their work if you’d like to delve deeper!

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In our climate change reading to date, we’ve found one concept to be clear: effects of climate change on caterpillars will be COMPLICATED. How a caterpillar will be affected may depend on its species, habitat, food plants, geographical location, or some combination of these variables. Not only are some species predicted to experience radically different effects than other species, individuals of the same species living in different places could also fare very differently.

And complication is a theme in the studies we’ve read about Woolly Bears. They might fare as well as ever, or even better than ever, in the face of climate change. They might fare worse. Or, some populations might do pretty well and others less well. Here’s what we know:

Remember that study from our last post, in which repeated freezing ultimately impeded many Woolly Bears’ ability to pupate? Well, Marshall and Sinclair undertook a similar project, in which they froze Woollies at 10*F. Some were frozen for 35 hours straight, while others were frozen five times for seven hours each, and allowed to thaw in between.

With each repeated freeze, the caterpillars were substantially more likely to suffer ultimately fatal injuries. Marshall and Sinclair didn’t observe the caterpillars through pupation, but guessed that the repeatedly frozen caterpillar survivors would be less likely to successfully pupate.

In their next study, Marshall and Sinclair used computer modeling as well as live Woolly Bear caterpillars to determine the impacts of snow cover on the caterpillars’ overwintering fitness. Their results surprised us! They found that caterpillars under snow (Woollies’ overwintering habitat of choice) used more energy over the winter than caterpillars exposed to the open air and allowed to freeze repeatedly. Apparently freezing has its benefits for Woollies—it allows the caterpillars’ body systems to be less active, so if they survive through winter, they will have more fat and a higher body weight.

Based on these studies, Woolly Bears may thrive in the face of climate change, if that simply means a warmer planet. As temperatures warm, their bodies may not freeze as often, leading to fewer fatal injuries. If temperatures are warm enough to eliminate snow cover, they may be exposed to freezing more often, when freezing temperatures occur, and staying frozen will help them conserve energy.

Wait… WHAT??? That doesn’t make sense!

So… the Woolly Bears shouldn’t freeze (especially repeatedly), so their bodies don’t get damaged. But… they should freeze (repeatedly, even), so they can use fewer stored fats.

And… climate change might freeze Woollies more often than before, because they’ll be protected by snow less often. But… climate change might prevent Woolly Bears from freezing because the temperatures could be too warm to freeze then.

Huh?

We warned you—it’s COMPLICATED!

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So, what’s the takeaway here? Are we just trying to confuse our readers with complicated and possibly contradictory information? No, we’re really not.

What we’ve gathered from these studies is a sense of positivity about Woollies’ future. They seem to have a “when life hands you lemons, make lemonade” survival strategy. There are pros and cons of both snow cover and a lack thereof. Repeated freezing might damage their bodies, but individuals that survive those conditions and go on to pupate will likely have large fat stores and be healthy adults. In fact, one of Marshall and Sinclair’s studies also showed that individuals that survive repeated freezing have MUCH more robust immune systems than individuals that aren’t repeatedly frozen.

We think Woolly Bears are going to be resilient and make the most of whatever climate change hands them, which is a better outlook than we have for some other caterpillar species.

Then again, this study took place in Canada, where Woollies are better adapted to cold than more southern populations. So what will happen to Woolly bears in other places? We can’t say without seeing some studies.

It’s COMPLICATED. But interesting. And important.

--Liz Kautz, TCL Education Director