The raid against the termite colony was a bloodbath. In the tunnels and on the dusty earth, termites fell by the score and warrior ants lost limbs and perished under the pincer shear of terrible mandibles. Yet the ants eventually prevailed.
Now, as the victorious ants survey the battlefield, they spy half a dozen living but injured comrades—many with legs severed clean by the the termite soldiers' viscous maws. Yet these wounded ants are lucky, for they are members of the species Megaponera analis; and unlike other ants, the injured warriors will not be left behind. In fact, after being carried back to the nest, some of these battle-scarred insects will harry forth in future raids later that day.
A team of ecologists and entomologists at the University of Würzburg, in Germany, have just finished an extensive study on the curious warrior's honor displayed by the Megaponera analis ants. These ants are found across sub-Saharan Africa. Erik Thomas Frank, who led the research team, meticulously tracked 420 raids in warring colonies in the humid savanna woodland in the northern Ivory Coast. The study was published this week in the journal Science Advances.
Leave No Ant Behind
To understand why these ants save their wounded companions, it helps to understand how the Megaponera analis ants conduct a raid. As Frank outlines in his paper, the ants follow a fairy routine pattern.
There are basically three castes of ants that take part in raids: the nimble scouts, large earth-mover ants Frank refers to as 'Majors', and the more numerous smaller infantry ants that Frank calls 'Minors'. Raids are initiated by scouts that, after returning to their nest upon spotting a termite colony, recruit "approximately 200 to 500 nestmates and lead them to the termites in a column-like march formation," writes Frank.
As the ants assault the dug-in termites, the Majors lurch to the front, stripping away barricades of "protective soil cover created by the termites, whereas the... Minors rush into these openings to kill and pull out the prey," writes Frank. These raids occur with impressive frequency. The ants wage war two to four times a day. After each raid, injured ants are inspected by their comrades' probing antennae as they curl up into a ball, and members of both battling castes are carried back to their nest to heal.
Being carried back by their companions, as apposed to trekking alone, is extremely important, Frank's team found. The scientists conducted several experiments that forced handicapped ants to retreat home in solitude after the war party had already departed. They found that roughly 32 percent of the lonesome veterans died en route, largely because they were singled out and attacked by predatory spiders.
Back in the safety of their nest, wounded ants are rapidly nursed back to health. They quickly became "accustomed to a four- or five-legged locomotion. and reached running speeds similar to those of uninjured ants 24 hours later," writes Frank, who adds that "nearly all injured ants were observed in subsequent raids." In one case, Frank found a de-limbed ant recover and embark on another raid a mere hour after its original injury! Now that's commitment to the colony.
For most colonial insects, the utility of a handful of damaged comrades is low, and so it's a rare sight to see creatures like ants tending to their wounded. But Megaponera analis ants form fairly small colonies—between 1,000 and 2,000 strong. Even a handful of saved soldiers (the ants returned an average of 13 battle-scarred warriors per day) makes a difference for such a small colony.
Using a simple computer model, Frank's team estimated how the side of the colony would be affected if injured comrades were left to die on the battlefield, or trek home alone. In part due the continual state of war of the small colonies, reports Frank, the no-ant-left-behind policy helps maintain a 28.7 percent larger colony size.
Frank argues that this boosted colony size is a large enough benefit to explain the evolution of this seemingly-altruistic behavior of saving wounded comrades. Still, we'd like to think that somewhere, somehow, there's an extremely tiny version of Saving Private Ryan taking place right now.