For the first time ever, scientists have observed interspecies warfare in bees — a spectacular natural phenomenon involving prolonged aerial battles and kamikaze attacks that result in thousands of fatalities in both attacking and defending colonies.
War is not uncommon among animals of different species (especially ants), but what is uncommon are fights to the death. Evolutionary theory suggests this is the case because alternative strategies that allow animals to assess strength and fighting ability, like physical displays, have emerged to let them avoid this costly behavior; the risk of death has to be outweighed by the benefits of obtaining the resource that's being contested, whether it be food, mates, or nesting sites.
But it appears that evolution has guided a certain species of stingless sugarbag bee, Tetragonula hockingsi, into adopting a rather bellicose strategy in which war is waged against a related species, Etragonula carbonaria, in order to gain unhindered access to a coveted honey-filled hive.
Researchers from Queensland University of Technology in Brisbane discovered that the invading bees use their jaws as lethal weapons in an effort to permanently remove the inhabitants of a targeted hive and install their own queen to rule. As observed by behavioral ecologist Paul Cunningham, the bees arrive in a swarm and clash jaws, locking the defenders in a "death grip" with their strong mandibles.
Remarkably, survival is not the intention of the individual attackers; this is a classic example of a hive mentality at work — a superorganism that places the well-being of the collective ahead of individual members.
"Neither the attacker nor defender survives in these one-on-one death battles, during which a carpet of dead and dying bees can be seen on the ground. It is a sheer numbers game as to who wins," noted Cunningham in a statement. "It took three consecutive attacks over several weeks before the hockingsi bees won out. When they eventually broke through the defences, they smothered the hive in a huge swarm, mercilessly ejecting the resident workers, drones and young queens. It was carnage!"
When the researchers first discovered the phenomenon, they had been expecting to find two colonies of the same species at war, but that wasn't the case. The attacking species appears to be coming into the Brisbane region from the north.
After the first fight, the invading bees backed off to regroup. But about a month later they returned with devastating results. They broke through the defence and sent workers into the hive to drag the young and inexperienced out of the hive to discard them. The third attacking wave proved to be the coup de grâce. The attacking swarm overwhelmed the defenders, who managed to escort a daughter queen into the hive to rule.
After the hive settled and down and there was no further fighting for several months, the researchers conducted a genetic analysis on the victorious bees. Results showed that a new queen was in residence and that she was indeed the daughter of the attacking colony's queen.
Since that initial case, the researchers have studied more than 250 hives around Brisbane and found evidence of 46 of these all-or-nothing takeovers over five years. This was not an isolated incident.
Andi interestingly, the hockingsi bees are not always the winners.
The researchers aren't entirely sure why the attacks happen, but it's likely a campaign for real estate.
"We still have many questions to answer, such as what instigates the attacks, and whether the young in the usurped hive are spared and reared as slaves, or killed outright," added Cunningham.
Read the entire study at The American Naturalist: "Bees at War: Interspecific Battles and Nest Usurpation in Stingless Bees". Supplementary information via QUT.