Colonies Maintain Temperature and Humidity

Biological Strategy

Ants

Leon Wang

Sense Temperature Cues From the Environment

Some living systems use their ability to perceive temperature to find prey or avoid predators, or as a way to gain information about their environment, such as whether they are near a warm or cold place. Temperature gradients can be subtle and modulate as they travel through water, air, or solids. Living organisms must therefore have a variety of thermal sensors appropriate to a given medium (liquid, gas, solid). Some even have a way to “visualize” a signal’s source. For example, the rattlesnake has heat sensors with thousands of nerve endings located in pit-shaped holes on each side of its face. The sensitivity of the pits overlaps, giving the snake a bifocal image of the heat’s source.

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Regulate Climate

Individuals and ecosystems manage local atmospheric conditions, thus regulating local climates. The local scale refers to climates such as those found under a shrub or within a forest. This local climate is called a microclimate. Regulating local climate creates favorable conditions, such as increased humidity or less severe winds, and contributes to species diversity. Microclimate development occurs over time: just from their presence, a few species initially able to tolerate the local conditions start to modify those conditions, resulting in microclimates that support others. For example, plants that live in alpine areas are subject to strong ultraviolet light, drying winds, and freezing temperatures. By growing together into dense clusters, these plants create a favorable microclimate that supports survival of a diversity of species.

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Cooperate Within the Same Species

A species is a group of organisms capable of breeding to produce fertile offspring. When individuals within a species undertake activities that benefit one another, that cooperation benefits not just the individuals, but also local and wider populations of that species. Collaborating in activities such as finding food, controlling parasites, and protecting from predators enhances overall survival. To cooperate, there must be enough benefit to an individual, and especially to a population, to justify any risk taken by individuals. Through cooperation, risk is distributed among individuals and the benefits to the community are greater than the sum of the benefits to individuals. An example is birds that gather in flocks, a cooperative activity more beneficial than acting alone. While some birds forage, others watch for predators. When one finds food, others also feed on it. Despite potential short-term competition for an individual that finds food, over the long-term, that same individual benefits when others find different food sources.

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Physically Assemble Structure

Living systems use physical materials to create structures to serve as protection, insulation, and other purposes. These structures can be internal (within or attached to the system itself), such as cell membranes, shells, and fur. They can also be external (detached), such as nests, burrows, cocoons, or webs. Because physical materials are limited and the energy required to gather and create new structures is costly, living systems must use both conservatively. Therefore, they optimize the structures’ size, weight, and density. For example, weaver birds use two types of vegetation to create their nests: strong, a few stiff fibers and numerous thin fibers. Combined, they make a strong, yet flexible, nest. An example of an internal structure is a bird’s bone. The bone is comprised of a mineral matrix assembled to create strong cross-supports and a tubular outer surface filled with air to minimize weight.

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Protect From Temperature

Many living systems function best within specific temperature ranges. Temperatures higher or lower than that range can negatively impact a living system’s physiological or chemical processes, and damage its exterior or interior. Living systems must manage high or low temperatures using minimal energy, which often requires controlling responses along incremental temperature changes. To do so, living systems use a variety of strategies, such as avoiding high or low temperatures, removing excess heat, and holding heat in. Insulation is a well-known example of managing low temperatures by retaining heat using thick layers of hair, fur, or feathers to hold warm air next to the skin.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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Colonies of South American grass-cutting ants maintain temperature and humidity via a thatched nest and systematic arrangement of nest material.

Ants are social insects with colonies that control their environment through collective building activities. Unlike underground species, the South American grass-cutting ant builds a thatched nest on the surface of the ground. A thatched nest is a mound structure formed from plant fragments and debris. This structure has a single central chamber where the ants cultivate fungi to feed their young (the brood). The ants must effectively regulate temperature and humidity within the thatched nest to provide ideal conditions for the fungus and brood. This is possible with the help of a thatched nest structure and the ants’ building behavior.

In the long term, the thatched nest provides a good amount of insulation. This is because the thatch material, compared to soil and the environment, reacts less quickly to changes in temperature. This limits the amount of heat that flows through the structure. Limited heat flow prevents the nest from overheating during the day and prevents major heat loss at night. The ants even place a five to ten centimeter layer of regurgitated grass fragments (called mulch) on the ground to limit the heat exchange between the fungus and the underlying soil. The nest’s insulation effectively entraps the internal heat generated by the ants and the fungi, enabling the fungus garden to remain five degrees Celsius above the average soil temperatures in all seasons. This is essential for favorable growth of the fungus and the brood, which prefer an optimal temperature of 24.1 degrees Celsius and high humidity.

In the short term, the South American grass-cutting ants display building behaviors to maintain the internal nest climate. As the nest reaches a temperature that might be harmful to the fungus or the brood, the ants create numerous openings in the thatched structure to allow the cooler air in from the outside to reduce the heat. However, the ants also show a response to any humid air leaving the nest by depositing material to close and seal openings. The colony constantly makes trade-offs between these two actions to locally control temperature and humidity shifts. Furthermore, these ants were found to deconstruct clusters or piles of material and relocate the items to allow for thatch turnover. This constant shifting of the thatch improves the insulation by moving the humid organic material (which has less insulation) from the inside of the nest to the outside, where it can dry more quickly. It also loosens the structure to provide better nest ventilation.

The nest of the South American grass-cutting ant is able to thrive due to the temperature and humidity control provided by its thatched structure and the active participation of the ants. The adaptations of this species have ultimately enabled it to extend its distribution range more in southern temperate regions compared to other subterranean species.

This summary was contributed by Leon Wang and Jack Mevorah.

Last Updated March 24, 2020

References

Journal article

The Thermoregulatory Function of Thatched Nests in the South American Grass-Cutting Ant, Acromyrmex heyeri

Journal of Insect Science | 28/09/2010 | Martin Bollazzi, Flavio Roces

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Reference

Journal article

Leaf-cutting ant workers (Acromyrmex heyeri) trade off nest thermoregulation for humidity control

Journal of Ethology | 12/02/2010 | Martin Bollazzi, Flavio Roces

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Reference

Journal article

Control of nest water losses through building behavior in leaf-cutting ants (Acromyrmex heyeri)

Insectes Sociaux | 05/03/2010 | M. Bollazzi, F. Roces

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Reference

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