The evolution of the caste system

Of course, we already know that a number of other social animals have evolved a soldier caste: ants, termites, and even some less socially-complex animals like aphids, snapping shrimps and flatworms. Yet until Grüter and his colleagues made their announcement, nobody had found bee soldiers.

I'm hoping for a follow-up article on soldier shrimp.

Why might Jatai bees have developed a class of soldiers while other bees apparently have not ? There is no definitive answer, but ... it turns out that robber bees pose a very real threat to Jatai colonies. If one robber bee encounters a Jatai colony and returns to its own colony to recruit more robbers for an attack, the result can be devastating, says Segers. "We have lost colonies to robber bees." This is why it is in the Jatai bees' best interests to attack a robber scout before it can relay its message.

"Ideally, the Jatai bee grabs the wings of the robber bee and doesn't let go," says Grüter, who has witnessed many such fights. Both bees fall out of the sky, the robber grounded by the soldier. They grapple with each other as the robber bee tries to tear away its tenacious attacker.

Eventually, the much larger robber bee usually succeeds in killing the Jatai soldier, often decapitating it in the process. But the dead bee's relentless jaws clamp on to its killer, preventing the robber from flying away. "The Jatai bees commit suicidal defence, lying on the ground with the robber bee until maybe an ant comes along and [takes] them away," says Grüter.
http://www.bbc.com/earth/story/20160728-jatai-bees-are-the-only-species-that-have-a-soldier-caste