All Ants Go To Heaven: How Ants Bury Their Dead

One of the first things I noticed while working with the turtle ants (Cephalotes varians) in the lab, after their surprisingly large size and interestingly-shaped heads (a cool example of evolution), was that they were carrying the dead ants in their colony around and placing the carcasses in the container with the food we had set out for them, which consists of bee pollen and ground crickets. This behavior was particularly confounding–the ants weren’t eating their dead (the carcasses were removed every week when we changed their food) so why were they putting their dead in the same place as their food? Initially, my research partner and I considered that perhaps the ants saw that their food container (including the dead ants) was removed and replaced every week, and so they were placing their dead there for the weekly funeral service to come and collect. However, this explanation felt unsatisfactory since it wasn’t founded in any real evidence or research.

[1] Inside a turtle ant colony box: seven deceased ants in the

container with bee pollen and ground cricket.

The behavioral pattern of carrying out the dead from the nests is actually a sanitation process called necrophoresis. Ants differentiate dead nestmates from live ones by chemical signatures. Some research suggests necrophoresis is triggered by the release of fatty acids, like oleic acid and linoleic acid, after death and the absence of other chemical signals of life.

These chemical signatures of death, oleic acid and linoleic acid, also trigger particular behavior in crickets, specifically avoidance of the corpses, and in honey bees, who also remove their dead from their hive. Given that crickets and ants both release the same fatty acids upon death and their behavior is impacted by its presence, perhaps the chemical signatures of the ground cricket could induce behavior in the ants? Specifically, if the ants detected the presence of these fatty acids in the mound of ground cricket, is it possible that the ants chose to pile up their dead next to the ground cricket because it already smells like a graveyard to them?

To investigate whether there could be a connection between the location of the ant graveyard and the presence of ground cricket, I talked to turtle ant expert Professor Donaldson-Matasci who explained a few things to me about turtle ant diets:

• Turtle ants are (mostly) herbivorous
• It is hard to observe what ants eat so their diets were discovered by comparing the isotope ratios of heavy and light nitrogen (15N/14N) in the ants’ bodies to that of other organisms in the same environment: plants have a low ratio, herbivores have an intermediate ratio, and predators have a high ratio.
• Professor Donaldson-Matasci’s prior research involved another species of turtle ant, Cephalotes rohweri, which are from Arizona, which she and her colleagues fed spam

So, we feed the turtle ants in our lab ground cricket as a potential source of protein, but we aren’t sure if the ants actually eat the cricket. Further observation is needed to determine whether the ants eat the ground cricket we set out for them; for example, weighing the initial amount of cricket compared to the amount of cricket at the end of the week. Additionally, we would need to determine whether there are even any detectable amounts of the fatty acids in the ground cricket, which could be accomplished in a number of ways, including using test strips specifically designed to test for the presence of oleic acid.

If we found that the ants do not actually eat the ground cricket and found that the fatty acids are still present in the ground cricket, I would think that it is possible for there to be a connection between the presence of dead crickets and the turtle ants leaving their dead nestmates in the same container. Perhaps the ants detected the presence of fatty acids associated with death and decided to pile their deceased nestmates in with the ground cricket. Further experimentation would be necessary; for example, we could separate the ground cricket and pollen into two dishes and compare the number of dead ants in each dish and outside of the dishes to determine if there is a significant difference in the location of accumulated dead ants. Ultimately, we have seen that ant behaviors, like feeding, can be elusive and there is still much to learn about our turtle ants. 

Further Reading:

Choe, D. H., Millar, J. G., Rust, M. K. (2009). Chemical signals associated with life inhibit 

necrophoresis in Argentine ants. Proceedings of the National Academy of Sciences, 106(20), 8251–8255. https://doi.org/10.1073/pnas.0901270106

Diez, L., Moquet, L. & Detrain, C. Post-mortem Changes in Chemical Profile and their Influence 

on Corpse Removal in Ants. J Chem Ecol 39, 1424–1432 (2013). https://doi.org/10.1007/s10886-013-0365-1

Russell, J. A., Moreau, C. S., Goldman-Huertas, B., Fujiwara, M., Lohman, D. J., & Pierce, N. E. 

(2009). Bacterial gut symbionts are tightly linked with the evolution of herbivory in ants. Proceedings of the National Academy of Sciences, 106(50), 21236–21241. https://doi.org/10.1073/pnas.0907926106

Sun, Q., & Zhou, X. (2013). Corpse management in social insects. International journal of 

biological sciences, 9(3), 313–321. https://doi.org/10.7150/ijbs.5781

Media Credits:

[1]: Photo by Professor Donaldson-Matasci