It’s not often that we learn about animals that commit suicide, but some ants and termites have evolved to have an explosive suicide as a defense mechanism to protect the colony from larger intruders.
The scientific term for this behavior is autothysis, which can be translated to “self sacrifice”, and has so far been seen is a few different species of both ants (Family Formicidae) and termites (Infraorder Isoptera). However, the phenomena has been best studied in colonies of ants, so this is what we will take a closer look at in this post.
Camponotus saundersi. Image by Bernard DUPONT, posted with the Creative Commons Attribution-Share Alike 2.0 Generic license.
The ants who have evolved this type of defense mechanisms have all been found on the island Borneo in Southeast Asia. The first species with this ability was discovered in 1935, and got the name Camponotus saundersi. So far all species with this ability has been arboreal ants, meaning that they are living most or all of their lives up in the trees in the jungle, where they use this mechanism to fend off other (larger) species of ants and other insects that poses a threat to them.
How the ants explode to protect the colony
When an exploding ant such as Camponotus saundersi realizes that the intruder it is facing is likely to win the fight, it goes into the self-destruction mode by having violent contractions on its abdominal muscles. By doing this it will rupture a part of its abdomen, which in turn will lead to the oversized mandibular glands bursting.
The mandibular glands are filled with chemicals, and these will be released from the front of the head of the ant when they burst. The chemicals are composed of polyacetates, aliphatic hydrocarbons, and alcohols, and are both corrosive and able to entangle all nearby victims.
Since parts of the abdomen is ruptured during this defense mechanism, the ant obviously dies from performing it. It's a bit grotesque, but this sticky explosion will be a big problem for the invaders or predatory insects who wants to get in to the colony, so it's a great defense for the colony as a whole. But why would an animal choose to perform suicide to protect the colony? This is a pretty complex subject that I could write several posts about, but we'll get to take a quick look at the big strokes of it.
Another image of the Camponotus saundersi. Image by Noel Tawatao / www.AntWeb.org, posted with the Creative Commons Attribution 4.0 International license.
Why it makes sense for the ants to kill themselves to protect the colony
Altruism in animals is a big and kind of controversial topic that I won’t be discussing in depth today, but the thing we know for sure about this topic is that we often see it in eusocial insects - insects that have complex social behaviors, including castes such as sterile workers.
These sterile workers are obviously unable to reproduce themselves, so in order to increase their fitness, they must work on increasing the inclusive fitness, which means that the offspring of related individuals are counted for, since these share many of the same genes.
You would share 50 % of your genes with your own child, but only 25 % of the same genes with your siblings offspring, meaning that it would give you a better overall fitness to make sure three of your siblings’ children survive to grow to adults compared to making sure one of your own children would (assuming you had to pick one).
It might sound really strange, but eusocial insects that are unable to get their own children have to depend on this inclusive fitness, and to make it even better for them, most of them share up to 75 % of the same genes (because they will get more genes from their mother - the brood queen), meaning that they get a big benefit from helping the colony survive.
By saving the colony it also prevents its sisters and mother from being attacked, which helps ensure that many sets of the shared genes are passed down to another generation.
This little introduction barely scratched the surface of the interesting topics of eusocial insects, and alternative ways of increasing the fitness of an organism, but hopefully you guys understand what I’m getting at with this.
The point is that the sterile workers of exploding ants are gladly willing to sacrifice themselves to protect the colony, and can even increase their inclusive fitness by committing suicide.
A new exploding ant species has been found
Ever since the first species of exploding ant was discovered in 1935, scientists have been searching the Bornean jungle for more species with the same behavior. Some new ants have been found, but due to taxonomic challenges (it’s not easy to do taxonomic studies on insects with castes that look unlike other castes of the same species), no new species has been officially described until this year.
Back in 2014 a research team from several different countries worked together to learn more about autothysis, but instead found enough evidence to describe a completely new species of exploding ant, the aptly named Colobopsis explodens. Up until this point it had been referred to as being a member of the Colobopsis cylindrical species group, that most likely has several different species of undescribed exploding ants within it.
So now we have two described species of exploding ants, but as the paper suggest, there could be many more new species lurking within the Colobopsis cylindrical species group.
Find strange defense mechanisms interesting? Check out the lizard that squirts blood in the face of its predators!
Thanks for reading
I hope you enjoyed the post about the exploding ants (and termites although we didn’t get into details about those). I think this is a really cool defense mechanism, but I’m also glad we don’t see it in any bigger species, because that would be messy. Hehe. Anyway, thanks for checking out the post!
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