A species of so-called ‘exploding ant’ from the rainforests of Borneo has been identified, the first of its kind to be discovered in over 80 years.
(Main photo credit: Alexey Kopchinskiy)
In the tropical rainforests of Southeast Asia, a group of canopy-dwelling ants exhibit a unique kind of defensive behaviour when faced with intruders.
When presented with a threat, workers of the group Colobopsis cylindrical – commonly known as ‘exploding ants’ – will literally blow themselves up. They will forcefully rupture their gaster, the bulbous part of their abdomen, in order to release sticky, irritant toxins in the direction of the enemy, with the intent to kill or repel.
These exploding ants were first documented in 1916 and later again in 1935, yet it is only now that the ants have been extensively researched and one particular ‘model species’ identified. The discovery came after five months of fields research conducted in the Borneo rainforest between 2014 and 2016.
Drawn by a collective fascination with these ants, a group of researchers hailing from Austria, Brunei, and Thailand set out to formally identify the various species of exploding ants. The group of entomologists, botanists, microbiologists, and chemists from the Natural History Museum Vienna, Technical University Vienna, IFA Tulln and Universiti Brunei Darussalam together identified 15 separate species of exploding ants. One species in particular, Colobopsis explodens has been taxonomically described for the first time, with researchers detailing all castes within the species.
Colobopsis explodens serves as the ‘model species’ for the entire Colobopsis cylindrica group across Southeast Asia, according to the paper published by the research team in the European peer-reviewed journal ZooKeys, which means that the recent research on this ant will act as a baseline for future research on exploding ants.
Autothysis: why and how?
In exploding ants, the act of self-sacrifice, or ‘autothysis’ as it is correctly known, is displayed during single combat, one ant pitched against another. If the challenger fails to withdraw, the ant will wrap itself closely around its enemy and self-destruct for maximum proximity impact. It is the minor workers that exhibit this autothysis behaviour and are “particularly prone to self-sacrifice when threatened by enemy arthropods, as well as intruding researchers.” The resulting ‘yellow goo’ secretions are very effective in immobilising intruders, but the rupturing of the abdomen always results in death for the exploding ant.
Autothysis is just one of many defensive strategies used by social insects, where individuals are sacrificed to protect the colony. “It’s a bit like the mechanism of when a bee stings,” explained Alice Laciny, the article’s lead author, an entomologist at the Natural History Museum in Vienna and a PhD student at the Department of Theoretical Biology at the University of Vienna.
The ants’ behaviour is similar to that of honeybees, which will sting an intruder, causing their own death. Similar behaviour is noted in some termite species, such as Neocapritermes taracua found in South America. “An ant colony shouldn’t be treated as a family of individuals, but really like a super organism, each ant acts more like a cell in a body and it has its own role to play, ” added Ms Laciny.
Although this exploding defence behaviour of the minor workers is very impressive, the major workers also have a defensive feature. Major workers, also called ‘doorkeepers’, have large, plug-shaped heads are used to physically barricade the nest entrances against intruders.
Although there are no exploding ants in Australia, there are a few species of ‘plug-heads’ – one species using this feature to plug up nest entrances when the tide comes in, to create a watertight seal!
Source: ZooKeys, Pensoft Publishers. ‘New ant species from Borneo explodes to defend its colony’. ScienceDaily, 19 April, 2018.
Journal reference: Alice Laciny, Herbert Zettel, Alexey Kopchinskiy, Carina Pretzer, Anna Pal, Kamariah Abu Salim, Mohammad Javad Rahimi, Michaela Hoenigsberger, Linda Lim, Weeyawat Jaitrong, Irina S. Druzhinina. ‘Colobopsis explodens sp. n., model species for studies on “exploding ants” (Hymenoptera, Formicidae), with biological notes and first illustrations of males of the Colobopsis cylindrica group’. ZooKeys, 2018; 751: 1 DOI: 10.3897/zookeys.751.22661