Welcome back.

We tend to think of resilience as something individuals build, but nature tells us something different. Every spring, thousands of tent caterpillars emerge and immediately get to work, spinning a collective silk shelter so well-engineered that it can hold 20°C of warmth while the world outside sits a minus 5. There’s no leader, just cooperation refined over millions of years.

Science journalist, Pragathi Ravi, returns in this week’s Life Finds A Way to explore one of nature’s most ingenious and underrated builders, and what we can learn from them about building our own climate-resilient urban designs.

Enjoy.

— Willow

When my partner turned 30 in May last year, he wanted to celebrate his birthday with a hike.

He looked up a trail that would lead us up Bull Hill or Mt. Taurus in the village of Cold Spring in upstate New York and loop back down to the village. The trail promised an arduous uphill hike, footfalls muffled by peaty forest floors, verdant stretches and magnificent views throughout. In the end, we would also see the crumbling Cornish Estate, which was ruined in a fire. 

Twenty minutes from the peak, as the early May air carried our breath, we started noticing something. It felt like someone had spun thin white silk on the tree branches. Upon closer inspection, we found it to be filled with worms— the abode of the tent caterpillar. This species (Malacosoma americanum) has evolved to create dense silk nets to nest in, socially and communally. A common sight in Spring across the Eastern US and southern Canada, these caterpillars form silken tents at the “crotches’’ of trees where the colony nests. The tents protect the insects from predators and aid in thermoregulation. 

The tent-building is actually the second step, says Emma Despland, a biology professor at Concordia University in Montreal, who has spent years studying this forest pest. They’re called pests because they can defoliate a tree, stripping it of its leaves entirely. The first step is group-living. 

When you peer into these tents, they are crawling with hundreds of caterpillars, clustered in close quarters. Despland calls them siblings, because a female moth laid a cluster of eggs.

“The caterpillars that emerge will be in a group. This species of caterpillar is among the first to emerge. They emerge come out in early Spring, when the new foliage is beginning to spring from the trees.”

They want to feed on the developing leaves because they are soft, often rich in protein and more nutritious. 

But to take advantage of this, they first have to weather the telltale signs of a departing winter, where the environment is still pretty cold for them to comfortably survive. As ectothermic (cold-blooded) animals, caterpillars rely on external heat sources to keep themselves warm. Their dark, hairy exterior absorbs heat, and huddling together amplifies this.

“They [become] a black mass, absorb more heat,” Despland says.

This is necessary because if they cool down, their metabolism slows, they become less active, and lose the ability to digest.

By spinning a tent of silk, the tents act as a miniature glasshouse that traps the sunlight streaming in from the morning sun. Researchers say this warms them quicker than they would if they were exposed outside. For instance, it could be minus 5°C outside, and the inside could still be 20°C.

Despland also points out that the caterpillars produce silk threads while they forage for fresh leaves. When they move along the tree, they lay down a thin strand of silk, so if they fall off the tree, they’re tethered to the thread. “This seems to be a pre-existing thing that's part of caterpillar biology,” she says. 

Andrea Battisti, an insect ecologist at the University of Padova, who has mainly worked with caterpillars in Australia and Europe, explains that the silk is produced from glands in the caterpillars' bodies, using the same basic mechanism as silkworms. The caterpillars collect amino acids, which react with oxygen to produce strands of silk. 

The construction of the tent itself is a collective act.

“It’s not an individual feat,” Battisti asserts. In a 2023 study, which is among the first to look at the social behaviour of these caterpillars during tent construction, his team found that the builders were predominantly male. Like Despand, he also believes this precise architecture was borne out of environmental cues. 

When temperatures drop below 0°C, the caterpillars will return to the tent and remain there—even if it is not as warm as in the mornings. They can survive up to a month without food if the temperature holds. When our body temperature drops below 37°C, Despland says, we contract hypothermia, which is life-threatening. But caterpillars can cool down without their body giving away, which allows them to rest out the harshest winter in the tent. 

Despland says that nature is full of such vibrant examples of partnership and synergy. 

She questions the definition of the “survival of the fittest.” The definition of fittest, she says, makes one think the strongest, toughest, most aggressive, but in some situations, the fittest might be the best collaborator, the one who cooperates most.

“The fact that we don't see them maybe says something about our own biases,” she adds. 

In terms of the cooperation that binds this community together, the researchers believe the ethos is innate– after all, they’re siblings. When they stay together within the tent, they evade the risk of being eaten. This kind of social organization protects them, says Battisti. “They're more likely to move when they're hungry, and if everybody’s hungry, then they’re in it together,” he points out.

According to Despland, nobody is a leader. “Their survival depends on being part of the group.”

While Despland and Battisti emphasize the survival-born cooperation of these insects, it’s hard not to see parallels in our joint efforts to resolutely adapt to the increasing climatic pressures of a warming planet. For the caterpillar, the fate of the cold nest affects all of them indiscriminately.

Something similar can be said about us, when intensifying heatwaves, storms, and hurricanes transcend geography and blur past neatly drawn state borders.

This has compelled architects and urban designers to devise more thermally resilient, adaptable cities, improving our microclimate, much like the caterpillars sought to modify their own surroundings. While investigating the relationship between urban microclimate and indoor thermal comfort, architects and urban designers have realized the importance of including dense trees to reduce heat stress and have installed green walls and roofs that offset increasing surface temperatures due to intense heat.

Urban designers have taken this a step further and used awnings and trees or “green roofs” to prevent overheating, incorporated cross ventilation to facilitate airflow and mulled over positioning buildings to block or trap sunlight. 

Credit to the caterpillar’s biological ingenuity, silk is popularly known for its insulation properties. This makes Despland think of the importance of using natural building materials while designing our buildings. In the older times, traditional materials and techniques were attuned to adapt to the weather of the season.

For instance, the 18th-century buildings in Quebec used this principle. The homes were built in a way that the balcony faces to receive the sunlight streaming in during the winter mornings, and traps that warmth indoors. This speaks to the brise soleil concept. Loosely translating to “broken sun”, this architectural design uses solar shades that are angled to control the heat seeping through a building.

Propagated by the Swiss-French architect and urban planner, commonly referred to as Le Corbusier, this design feature is designed to let the low-level sun enter the building during winter. The knowledge of the sun’s arc-based travel from east to west allows designers to effectively trap the winter sunlight, but eliminate direct summer heat, an intuition that is much like the caterpillar’s season-based adaptation skills. 

In the spirit of biomimicry, researchers have realized the value of emulating animals in their natural surroundings, taking cues from their efficient strategies for adaptation.

The use of natural building materials, which are much more attuned to managing heat, is gaining traction. We have evidence of how constructing tall concrete and glass towers has trapped us in an ‘urban heat island’ that is slowly making dense urban environments less livable. The tightly woven silk of the tent works like double-paned glass: layered, insulating, trapping warmth within while keeping the cold at bay.

The caterpillars do not navigate the cold alone.

They build, share and resist together. These systems of biology can serve as a blueprint for how human society can take on the common challenge of climate change.

The climate crisis doesn’t discriminate. It will ask of us exactly what it asks of the tent caterpillar: stop going it alone.