Borneo’s Camponotus cylindricus ants are a little touchy: if they encounter a foreign ant in their territory, they will latch onto its legs with their jaws and then quite literally blow themselves up, spraying a sticky yellow substance over the unlucky intruder. Not exactly the most level-headed reaction, but an effective one for defending the ant’s territory. A recent study in the journal Acta Zoologica describes how these volatile buggers release their noxious lather: by squeezing themselves to death with their abdominal muscles.
When it comes to “yellow goo”—the researcher’s actual technical term for the post-squish spritz—these ants are literally full of it. The reservoirs that house the liquid make up as much as half the volume of the ant’s body and stretch from the base of the head to the tip of the insect’s abdomen. The goo is made up of various irritating chemicals and strong adhesives that permanently bind the body of the dead Camponotus to the attacker. This enemy ant becomes subdued by the noxious chemicals, as well as the fact that it’s, well, forever glued to a corpse. After locking an enemy in a death grip, these ants bend and compress their abdomens so forcefully that the liquid violently ruptures out of several points on their rear-end. They aim for enemy’s faces, maximizing the power of the irritants and ensuring an immobilizing “attachment.” In your face!
Although it may sound a little extreme, this kamikaze tactic serves to protect the ant’s nest and territory. Self-sacrifice is not uncommon in highly social animals, such as termites and honeybees that will fight to the death to protect the queen. Similarly, soldiers from one termite species will emit a glue-like material to trap anything attacking its colony, sometimes dying from the stress of the excretion. But Borneo’s exploding ants will even self-detonate far from their colony, or when lightly touched with forceps in the lab. Some studies have shown that the ants will leave certain smaller-bodied “enemies” alone, saving their suicidal spurts of putridity for larger ants. The strategy—trading a life for a life—seems designed to win a war of attrition against larger-bodied ants that may have lower populations.
So how did this rather unorthodox technique evolve? Some closely related ants have similar reservoirs that can house symbiotic microbes which help to digest plant matter [PDF]. Researchers speculate that some of the chemicals in the exploding ant’s yellow goo initially helped them break down the microbes and microbial by-products they feed on. Some of these compounds, such as irritants more commonly found in fungi, may have then proved useful in deterring enemies and led to the exploding adaptation.