New research shows that humidity helps insects manage their tasks. Termites are often called nature’s architects. The nests, which reach several meters in height, have structures that are complex and detailed enough to make engineers jealous, and have galleries that provide efficient communication and automatically ventilate the interior of the nest. How can thousands or millions of insects coordinate their efforts to build strong and functional nests for the colony?

The new study, coordinated by Andrea Perna, Professor of Complex Systems at the IMT Lucca School of Advanced Studies, and published in the journal e-Lifeidentified a unique mechanism that termites use to perform such extraordinary tasks.

Conducting your laboratory experiment on termites of the Coptotermes species gestroi (native to South Asia but spread to the East Coast of the United States) researchers created small arenas with artificial structures of various heights and shapes using wet clay.

They then collected small populations of termites from a larger colony and measured building behavior in response to these structures through video surveillance of the activity of all termites in the population while characterizing changes in 3D structure. In this way, different hypotheses can be tested to reveal the coordination mechanism used in nest construction.

Comparative ideas and experiments

In the case of termites, another large group of insects that can, for example, build large and complex structures, ants, it is believed that the ants penetrate the building material with pheromone, a chemical that attracts other ants to their structures. construction site and “tells” them where to build. Thus, the action of one worker ant triggers the activity of other ants in the process of self-reinforcement.

If termites, like ants, rely on pheromones to direct their construction activities, they should not choose to deposit pellets of construction material in a particular location, because artificial arenas prepared by termites do not contain any pheromones. Experimenters But this was not the case: Collections of pellets occurred all over the arena, while all the debris was collected on top of pre-existing structures. Maybe they can estimate the height of small pillars and irregularities in the ground so they can continue adding building material on top of existing structures. But this was not the case: In fact, termites deposited construction particles on both short and tall poles with equal probability.

Another hypothesis was that termites could sense the curvature of the building substrate; Some previous simulations showed that continuous addition of granules at places of greatest curvature was sufficient to form very complex structures resembling the nests of some termite species. “During our simulations, we observed that small surface inhomogeneities have a higher curvature than the surrounding flat substrate and therefore expand to form a column, while the pointed ends of the columns attract more debris of building material and continue to grow until they separate or merge with another column.” etc.; Very complex structures can be created with this simple rule,” says Giulio Faccini, first author of the study and a researcher at the Institut Matière et Systèmes Complexes CNRS in Paris, France.

In fact, when faced with artificial stimuli provided in experiments, termites always preferred to build in places with the greatest curvature, adding pellets to the top of poles (regardless of their height), and when provided with a small wall stimulus. They continued to add pellets, mostly at the two corners of the wall, the two points where the curvature reached its maximum.

Understanding the sensory abilities of termites

The question is, how were termites able to so reliably detect the curvature of the structures they built? The researchers had a clue that water evaporation and humidity might be involved. “Termites are very sensitive to moisture concentrations: Unlike most other insects, they have a thin exoskeleton and soft skin, meaning even prolonged exposure to humidity levels below 70 percent can be fatal for them,” Perna explains. “It’s not surprising that they can sense these humidity changes and respond to them with their behavior.”

But how can we prove this? “We found what was described as a ‘very ingenious, low-tech solution’: one of the magazine’s anonymous reviewers e-Life : We prepared experimental areas identical to those used for termites, but this time we saturated the clay with a saline solution. sodium bicarbonate. When the water in the salt solution evaporated, it left behind small salt crystals; their growth marked the areas where the greatest evaporation occurred: these were the ends of columns, the corners of walls: exactly the same areas that termites chose for their construction activities. !” explains Fakini.

“We were really surprised to see that termites provided such a simple solution to a very complex problem,” Perna says. “In our experiments, nest complexity arises from one simple mechanism: Termites only need to add pellets of material based on local humidity, but the pellets they add also change the entire pattern of evaporation and moisture, causing other termites to settle elsewhere, etc., until very complex structures are formed.”