When are they Dead? – Issue #104

Hello Explorer,
During my studies the same question came up repeatedly, when is a tree considered to be dead? This might seem like a strange question at first, but as you start delving into the answers you quickly realise that there is much more to take into consideration.
The lines are blurry when a tree is actually dead, but there is one certainty, the point of no return. The point of no return is when a tree’s defences are overwhelmed, and the tree will die without any chance of survival. The main question, however still stands: When is the tree dead? When it has lost all of its leaves? When it stopped photosynthesizing? When all the growth points on the tree have become inactive? When it stops transporting nutrients between the various parts of the tree? When it stops transporting water from the roots to the leaves? All of the above?
The definition of a dead tree changes with the specific study or use of the tree, as a tree that stopped bearing fruit and is losing its leaves might be considered dead to a farmer, but to an ecologist it may be in a declined state only.
A few weeks ago I have lost one of my Tawny Balbyter (Camponotus fulvopilosus) queens and that sparked a lot of questions. The main one being, when is a colony dead? Is it when the queen dies? Is it when too many workers die? Is it when there is an imbalance in the castes present in the colony? Is it when they have abandoned their nest?
A colony can likely not be considered completely dead when there are still workers of the colony alive, but is it so simple? Because if you have ten workers without a queen or brood, the workers might be alive, but the colony is already dead.
If the queen of the colony is lost, they lose the ability to reproduce, and with her queen pheromone gone the ants tend to become sluggish, and almost hopeless. They will sit in the nest and not forage or move around much. In some species, however, the death of the queen might even go unnoticed, as I suspect is the case with The Pugnacious Ant (Anoplolepis custodiens) as they have multiple queens and during nuptial flight the colony will take more queens hostage and drag them into the nest.
Vice versa again if the queen is alive, but the colony loses most of the workers, the colony won’t be able to gather enough food to stay alive. The brood will die, and the colony will diminish quickly and not have much hope of survival. In this case the question is where is the point of no return, from where the colony has no chance of survival? And does reaching the point of no return mean that the colony is dead?
Similarly, if an ant colony raises to many soldier caste workers and too few workers, they would not be able to tend to brood and the colony would face the same fate as one who loses most if its workers.
Can ants be considered dead if they abandon their nest? Not in the sense of moving to new nesting location but abandoning the nest without a new nest to go to. This has the potential to lead to desiccation and death of the colony, or to the dispersal of the colony, and subsequently the death, as the queen and the workers with her might not be enough to survive on their own.
Ecologically speaking, I would hypothesise that an ant colony is dead once they stop fulfilling their ecological roles, like soil engineering, seed distribution, predation, farming of honeydew producing insects, etc. When they stop fulfilling their ecological role, they should be considered dead, as they no longer have an impact in the ecosystem as the living super-organism a colony is. They might have post death impacts on the ecosystem, like when an elephant’s heart stops, it flops over, and is dead. The elephant still has great ecological impact, but not the same as when it was alive. The ant colony might have dug deep tunnels that can be inhabited by other animals, there might be more seeds that are stored in the nest that germinate than usual, the tunnels might collapse and the soil engineering effect they had on the ecosystem is reversed, but these are all post death impacts.
From an ant keeping perspective, if the colony was kept for a long time and the person is attached emotionally to the ants, it might only be considered dead once the last ant of the colony dies. This might also be the case for research colonies that are being used for various experiments.
Determining when an ant colony is considered dead is a complex and multifaceted question. It's not simply an instant event like in the case of vertebrates (Remember our elephant, heart stop, flop over, dead), but rather an ecological process that unfolds gradually. The definition of death can vary depending on the specific context, whether it’s for ecological purposes, research, or ant keeping and personal attachment.
Have you ever wondered when a tree is actually dead? Have you ever thought about when an ant colony is dead? What is your perspective on when an ant colony is considered dead?

If you would like to send me a message with your answers, feel free to do so on Instagram or Twitter @abugmanslife or via email to [email protected].

References:

Franklin, J. F., Shugart, H. H., & Harmon, M. E. (1987). Tree Death as an Ecological Process. BioScience, 37(8), 550–556. https://doi.org/10.2307/1310665

Next week I will delve into the art and challenges of Ant colony death in terms of pest control, as that is a whole topic on its own.