Last updated May 3, 2018 at 9:53 am
Self-sacrificing workers shower their enemies with toxic goop.
Exploding behavior of C. explodens in experimental setting with a weaver ant. Credit Alexey Kopchinskiy.
There’s a lot of complex behaviour among ants that we don’t truly understand yet. But it doesn’t come much more dramatic than that of the “exploding ants” – Colobopsis cylindrica – which actively rupture their body walls to spray sticky, toxic goop as a last line of defence against their enemies.
This fatal behaviour was first noticed in 1916 and we know of about 15 separate species of these ants which navigate the dense canopy of rainforests in Southeast Asia. But through lack of evidence and research, no new species has been officially described since 1935.
Now an interdisciplinary research team from Austria, Thailand and Brunei has described a “model” type for the insects, appropriately named Colobopsis explodens, found in Borneo’s jungles.
Defence strategies
Secreting a bright yellow poisonous substance from its glands, the species’ minor workers are “particularly prone to self-sacrifice when threatened by enemy arthropods, as well as intruding researchers”.
Only this caste is responsible for either killing or delaying invaders. Major workers have other strategies. They have developed large, plug-shaped heads that can physically block off nest entrances and tunnels from the enemy.
Major worker of C. explodens with characteristically enlarged head. Credit Heinz Wiesbauer.
But it was the more dramatic suicide mission that intrigued the scientists from the Natural History Museum Vienna, Technical University Vienna, IFA Tulln and Universiti Brunei Darussalam.
So far the researchers have made two trips to observe the ants. The first began foundational work recording the ants’ routines, conducting experiments on food preferences, and collecting details of the ants’ anatomy, chemical profile and evolution.
During a second trip, team members Alexey Kopchinskiy and Alice Laciny sampled the first males of these ants to be observed, and witnessed a mating flight with anticipation.
While many details about exploding ant biology remain undiscovered, the model species will become a significant marker for any future studies.
Out with a bang
This fascinating mechanism of self-sacrifice, which is also known as autothysis, is a rare behaviour but not unknown. Some termite species use it as a defence mechanism.
The termite Neocapritermes taracua, found in the rainforests of French Guiana, for example, use something similar. The workers grow white “backpacks” on their abdomens, and over their lifetime, develop a toxic blue liquid filled with copper-containing crystals.
When an enemy invades their nest, these individuals scuttle to the top and release the substance, sacrificing themselves in a triumph for the colony.
Honeybees also exhibit a fatal defence tactic – when threatened by a larger animal, or even ourselves as curious human beings, this bee species eject their stingers into the skin, along with two backwards-facing barbs.
This feature makes it impossible for the bee to pull the stinger back out, and as it flies off, its complete stinging apparatus is pulled from its abdomen in a lethal twist.
This study was published in the open access journal Zookeys.
