Article written by Matthew Wheelwright

Published & edited by Janire Castellano

Ants are famous for their collective behaviour. They will often work together to build amazing structures which help make their local environment more favourable for them. In this blog post, I’ll be going over a few of my favourite examples.

April Nobile / © AntWeb.org / CC BY-SA 3.0

When it comes to architecture in the insect world, ants are true artisans. For decades, researchers have marvelled at the intricate structures which allow them to control the environment around them and make even potentially hostile environments suitable for them to thrive in.

One of the most striking examples of this is built by a species of leafcutter ant (Atta vollenweideri). This species builds its nests in dense, clay-rich soils which is potentially problematic since air cannot easily permeate through this type of soil and thus could lead to either a lack of oxygen or a build-up of carbon dioxide within the nest, both of which would be detrimental to the survival of the colony. To avoid this, these ants build a series of ventilation tunnels within their nests which facilitate the flow of fresh air throughout the nest which ensures that there is enough oxygen to support not only the colony itself but also the symbiotic fungus which it cultivates for food as well as ensuring that the level of carbon dioxide within the nest remains low (Kleineidam et al. 2001). This system consists of a series of tunnels which each have two openings: one at the base of the nest mound, one at the top. The two openings being at different heights is what allows the ventilation system to work due to Bernoulli’s principle (Kleineidam et al. 2001). Bernoulli’s principle states that the higher the velocity of a fluid, the lower its pressure and, since wind moves past the top of the mound faster than the bottom, the air at the opening at the top has a lower pressure than the air at the bottom which means air is pulled in through the opening at the base (the inflow opening) and out through the opening at the top of the mound (the outflow opening) (Kleineidam et al. 2001). This effect is strengthened by the presence of turrets which the ants build at the outflow openings which increase the height of the outflow opening which makes the pressure difference more pronounced and is thus thought to improve the efficacy of the ventilation system (Halboth and Roces 2017). The ants may also alter the structure of these turrets in response to changes in environmental conditions. For instance, it was noted that, after heavy rains, the ants would build the turrets higher, presumably to help prevent water from entering the nest (Jonkman 1980). More recently, it was also found that high levels of carbon dioxide in the air, which may be an indicator of poor nest ventilation, causes the ants to build more openings in the turrets which is thought to increase their effectiveness by increasing the total aperture size of the openings (Halboth and Roces 2017).

Other species of ant demonstrate engineering excellence, not because of the complexity of the nests they make but because of the novel materials which they use to make them. Perhaps the most famous example of this is the weaver ants (Oecophylla sp.). Weaver ants derive their common name from the fact that the workers use the silk produced by the larvae to “sew” together leaves to form the nest (Hölldobler and Wilson 1977) (perhaps their other common name, the tailor ant, is a more fitting title). It is not just this stitching which relies on amazing cooperation between nestmates. When the gap between two leaves which are going to be stitched is too big for one ant to bridge alone, the workers will form chains to cross the gap and then as a team pull the leaves together and then hold them in place until the silk has been applied (Hölldobler and Wilson 1977). The whole process is perhaps one of the clearest demonstrations of the level of cooperation which occur in colonies of social insects.

But it is not just when building their homes that ants demonstrate their aptitude for architecture. Some species, for instance, will construct solutions to deal with problems encountered whilst out foraging. An example of such a species is the red imported fire ant (Solenopsis invicta). A recent study (Wen et al. 2020) showed that when these ants encounters a surface which is unsuitable for walking on because it is physically difficult to do so (in the case of the experiment, this was due to the surface being covered in double-sided tape or liquid paraffin) or because it is coated in a substance which the ant finds repellent (essential balm in the case of this experiment) then they will simply pave over it by covering it in soil which then allows them to reach areas which would otherwise be completely inaccessible (Wen et al. 2020). A more recent study has shown that these ants will even use soil to cover areas which have been covered in insecticides and doing so can reduce their contact toxicity (Wen et al. 2022), which may have major implications for the control of this species. Perhaps the most interesting question raised by these experiments is: how did this behaviour evolve? Since the substances used in these studies would be rarely encountered by ants in the wild, it seems peculiar that such a behaviour would emerge in this species. However, the researchers have come up with a compelling theory as to how it happened. They believe that, since these ants are native to areas which are prone to flooding, this behaviour was originally a response to areas of soil which were impassable because they were waterlogged. They posit that ants which exhibit this behaviour would have a selective advantage because it would potentially allow them to have access to resources which other species of ant would not (Wen et al. 2020).

Despite their superficial differences, one thing that all of these species beautifully demonstrate is that despite being relatively simple creatures on an individual level, as a colony, ants can shape their environments in a variety of incredible ways and prove that they are the true architects of the insect world. Who knows what other marvels of engineering lie undiscovered in the nests of these beautiful creatures, I for one cannot wait to see what discoveries come next.

References

Halboth, F. and F. Roces (2017). The construction of ventilation turrets in Atta vollenweideri leaf-cutting ants: Carbon dioxide levels in the nest tunnels, but not airflow or air humidity, influence turret structure. PLoS ONE 12(11): e0188162. Doi: 10.1371/journal.pone.0188162

Hölldobler, B. and E. O. Wilson. 1977. Weaver ants. Scientific American. 237: 146-148, 151-154

Jonkman, J. C. M. (1980). The external and internal structure and growth of nests of the leaf-cutting ant Atta vollenweideri Forel, 1893 (Hym.: Formicidae). Part I. Zeitschrift für Angewandte Entomologie 89(1-5): 158-173. Doi: 10.1111/j.1439-0418.1980.tbo3454.x

Kleineidam, C., Ernst, R. and F. Roces. (2001). Wind-induced ventilation of the giant nests of the leaf-cutting ant Atta wollenweideri. Naturwissenschaften 88: 301-305. Doi: 10.1007/s001140100235

Wen, C., Chen, J., Qin, W.-Q., Chen, X., Cai, J.-C., Wen, J.-B., Wen, X.-J. and C. Wang. (2020). Red imported fire ants (Hymenoptera: Formicidae) cover inaccessible surfaces with particles to facilitate food search and transportation. Insect Science 0: 1-13. Doi: 10.1111/1744-7917.12891

Wen, C., Shen, L., Chen, J., Zhang, J., Feng, Y., Wang, Z., Chen, X., Cai, J., Wang, L., He, Y., Wen, X., Ma, T. and C. Wang. (2022). Red imported fire ants cover the insecticide-treated surfaces with particles to reduce contact toxicity. Journal of Pest Science 95:1135-1150. Doi: 10.1007/s10340-021-01474-0