Month: March 2025

Ant engineers: how team transport inspires tomorrow’s robotics

/ Damien Gergonne / Leave a comment

By Carmen Gil-Hoed

In this blog, Carmen, a biology student at the Autonomous University of Madrid, describes how ants team up to carry food that’s too big for one ant alone. She reveals how they coordinate their efforts—and sometimes struggle—to get the job done. Their teamwork is so impressive it even inspires robotics research! Read her latest article in Insectes Sociaux here.

While foraging, ants often encounter food items too large for a single worker to carry. To overcome this challenge and optimize food intake by the colony, some species have evolved cooperative transport, a behaviour in which multiple individuals work together to move an object that is too large for a single ant to carry. Aside from humans, ants are the only animals known to regularly engage in large-scale cooperative transport (Czaczkes & Ratnieks, 2013).

The study species, Anoplolepies gracilipes. ©Sarnat (2008)

Why not all ant species engage in cooperative transport? And why do we see such a wide range of abilities? From species where the transported objects seem to fly directly to their goal, to others where there is no coordination and movement is slow and inefficient. By describing the well-coordinated cooperative transport in the invasive ant Anoplolepies gracilipes, we hope our work brings us closer to answering these questions soon.

We studied whether A. gracilipes ants visit a foraging area with Diacamma rugosum footprints and how the presence of these footprints affected their decision to cooperatively transport food by using a Y-maze. We tested three experiments: D. rugosum footprints Vs. nest matesfootprints, D. rugosum footprints Vs. No footprints and nest mates footprints Vs. No footprints. During the test runs we recorded the retrieval time for each item, its weight, the number of ants involved in transport and their positions.

The experimental set-up. Three arm combinations were tested using a Y-maze. ©Carmen Gil.
Here is an example of Crazy Yellow Ant engaging in the cooperative transport of a 0,11g cockroach. ©Carmen Gil.

96 times out of 144 (66.7%) the cockroaches were successfully transported to the nest through a tight (3 cm) paper branch. This indicates a high level of coordination among the ants. When the ants failed, they mostly did it by falling out of the paper branch. This shows that while the ants seem strong enough to carry the load, navigation errors can occur. Suggesting that the biggest challenge during the transport is the coordination of forces.

One thing we observed was that the number of workers involved in cooperative transport increased with the load’s weight. This pattern is consistent with findings in other ant species like: Eciton burchellii and Dorylus wilverthi (Franks et al., 2001). It demonstrates that ants can assess transport difficulty and determine the necessary number of individuals for the task. However, the underlying mechanism behind this decision-making process remains unclear and needs further investigation. Another interesting finding is that the probability of successfully carrying an item to the nest increased with the number of ants involved in the transport and decreased with the weight of the prey item. Further, we observed that while A. gracilipes ants adjusted the number of carriers during transport, they appeared to reach a saturation point beyond which no additional ants joined. These results suggest that having more workers in the transport group than necessary may lead to wasted effort (McCreery and Breed, 2014).

The cooperative transport in Anoplolepis gracilipes. The number of ants engaged in cooperative transport increased with the weight of the transported item.

Cooperative transport is an intriguing behaviour as it requires coordination of movements and efforts among multiple individuals. Further research should investigate the mechanisms underlying the stability of transport groups, focusing on the rules that determine when ants join or leave and how they overcome navigation failures. Cooperative transport has multiple applications such as in the field of robotics. A recent trend in Artificial Intelligence and Operations Research takes inspiration from social insects, using them as a model for developing problem-solving techniques and optimization algorithms. This same idea fuels swarm-based or collective robotics. Researchers design distributed control systems that let groups of robots work together efficiently, taking as an example the cooperative transport done by ants (paper de robotics) so robots can reach a form of decentralized decision-making.

References:

Czaczkes T, Ratnieks F. 2013. Cooperative Transport in Ants (Hymenoptera: Formicidae) and elsewhere. Myrmecological News 18:1–11.

Kube, C. R., & Bonabeau, E. 2000. Cooperative transport by ants and robots. Robotics and Autonomous Systems, 30: 85–101. doi:10.1016/S0921-8890(99)00066-4

McCreery HF, Breed MD. 2014. Cooperative transport in ants: a review of proximate mechanisms. Insect Soc 61:99–110. doi:10.1007/s00040-013-0333-3

Franks NR, Sendova-Franks AB, Anderson C. 2001. Division of labour within teams of New World and Old World army ants. Animal Behaviour 62:635–642. doi:10.1006/anbe.2001.1794

How does a caterpillar use its tentacles to get the attention of ants?

/ Damien Gergonne / Leave a comment

By Amalia Ceballos-González

In this blog, Amalia from the University of São Paulo tells the story of how she and her colleagues studied a strange functional behaviour in a myrmecophilous riodinid caterpillar. Read her latest article in Insectes Sociaux here.

Caterpillars that establish close interactions with ants have developed various adaptations to maintain the ants’ attention. These adaptations involves specialized organs that produce nutritional rewards or chemical signals to attract ants. The butterfly families Lycaenidae and Riodinidae provide many examples of myrmecophilous caterpillars, including species with these organs. In our recent study, published in Insectes Sociaux, we explored the impact of these specialized organs on ants by focusing on a species from the less-studied family Riodinidae, Synargis calyce, which interacts with various ant species. In our study area, the most frequent interaction involved the ant species Camponotus crassus.

Caterpillars of Synargis calyce interacting with different ant species. (a) With Camponotus crassus, (b) with Camponotus renggeri, (c) with Wasmannia auropunctata, and (d) with Paratrechina longicornis. ©Amalia V. Ceballos-González.

Caterpillars of this species possess two pairs of tentacular organs. The first pair, known as ATOs (Anterior Tentacle Organs), likely release volatiles that influence ant behavior, although there is insufficient evidence to confirm this. The second pair, known as TNOs (Tentacle Nectary Organs), secrete a nutritive substance (primarily composed by sugars and amino acids) that ants consume. Whether these organs work synergically or if one is more relevant than the other was still unclear for our study species and it is also the case for many other species of the family Riodinidae.

Illustration showing the position of the tentacular organs (TNOs and ATOs)  in a caterpillar of the Riodinidae family. Below, a photograph of Synargis calyce indicates the two pairs of tentacular organs with arrows (Yellow = ATOs, Blue = TNOs). Drawing adapted from DeVries (1991). ©Amalia V. Ceballos-González.

To uncover those aspects, we aimed to explore this pair of tentacular organs by checking ants’ reaction. Our research was conducted at the University of São Paulo, Ribeirão Preto campus. Our first objective was to create an ethogram documenting the behavioral interactions between caterpillars and ants. During these observations, we identified a striking behavior. The ethogram revealed that after the eversion of ATOs, ants exhibited stereotyped “jumping” behavior. This behavior involved ants rapidly lifting their legs and jumping towards the caterpillar’s head.

 Synargis calyce caterpillar interacting with a Camponotus ant.

Next, we conducted experiments in which we experimentally manipulated – by allowing or preventing them to evert – the two types of caterpillar organs (TNOs and ATOs), to determine their role in maintaining ant attendance. Our findings demonstrated that TNOs are more effective in maintaining the attention of attendant ants, likely due to the rewards these organs provide. However, we also found that caterpillars with only functional ATOs received more attention compared to those with neither organ functioning. This indicates that TNOs play a central role in sustaining ant-caterpillar interactions, while ATOs serve a complementary function.

Three caterpillars (possibly third instar) interacting with Camponotus ants.

In conclusion, the interactions between S. calyce caterpillars and attendant ants are primarily driven by the rewards produced by TNOs, with ATOs playing a smaller, supportive role. These findings are consistent with observations in Lycaenidae species, which exhibit similar mutually beneficial relationships with ants. The evolution of these organs may represent a case of convergent adaptation to environmental pressures experienced by caterpillars in both families.