The Bee Ball – Bee Thermal Defense

Gangs of Asian giant hornets attack bee nests, killing all the workers before stealing the larvae for food. The little bees can’t sting through the thick hornet armour. See Cracked.com’s 5 Most Horrifying Bugs VS Scott’s 5 Most Horrible Worms for more on that.

So instead, the Japanese honey bees use a novel defense behaviour. They cook the hornet invaders to death.

As the hornets aproaches the nest, around a hundred bees will gather at the entrance and keep it open to draw the hornets in. Once a hornet is in, about five hundred bees rush the intruder and grab onto it, immobilizing it.

The bees then start vibrating their wing muscles, producing heat and raising the temperature to 47 degrees Celcius. The bees can tolerate such temperatures, but the hornet finds even 45 degrees fatal.

Thus the smaller bees overcomes the hornet tanks with their own version of Molotov cocktails. This interesting tactic is called the ‘bee ball’, or more technically, ‘bee thermal defense’. See Wikipedia article for more details.

     Bees mobbing a hornet, which is stuck inside the ball.

You can watch a 5 minute 51 second video of a gang of big bad hornets bullying and decapitating little bees, followed by an example of bees fighting back with a bee ball attack (with a graphic of the temperature increase in the ball). Video here.

Much bigger hornet on the right, just before biting the head off a bee.

The bees in pro wresting royal rumble action! You can just see the wider stripes of the hornet contrasting with the smaller bees.

                                    Bee-ware the fire-beeball!

This really cool bee-haviour (lol) strikes me as extremely complex to evolve randomly. So How did this very complex behaviour come about through Darwinian evolution?

Here’s the hypothesis: Since evolution favours the adaptations most suited to survival and propogation of the next generation, the bees must have been subjected to a life-or-death challenge from the hornets. True, since the hornets wipe out an entire bee colony in each attack.

Some (or even only one) of the bee colonies must have had the incredibly lucky, coincidental and pure random chance quirk of its workers tending to behave like hippies giving group-hugs-for-everyone. Throwing themselves at the hornet, their hot free love happened to overwhelm the invader.

If none of the colonies at all had this chance reflex, there would be no more honey bees for hornets to prey on them. Or if the hornets had a higher temperature tolerance than the bees, the tactic would fail miserably as the overheated bees die and fall off one by one.

The few (or one) colonies with the chance successful bee balling behaviour went on to reproduce via alates (princes and princesses). Now, the queen which produced these alates must already have been lucky enough to carry genes that produced the quirky bee ball behaviour in the workers.

Some of the alates on their mating flight must be lucky enough to carry the genes for bee balling. That’s a given, seeing as how many alates are produced. Some of the gene carriers must be lucky enough to survive the subsequent mating and found a colony.

From the mating, the genes for bee balling must be lucky enough not to be overwhelmed by non-bee balling genes (which may be dominant). This problem is solved if all non-bee balling genes have already been wiped out by hornet attacks on the bee colonies.

The new colonies must next be lucky enough to survive any challenges… Including early hornet attacks (before the bee ballers are ready) and non-hornet threats. The latter is especially poignant since by selecting for bee balling behaviour over other fitness factors (such as resistance to disease), other fitness factors may be lower.

And finally, this series of happenstances must successfully continue for generations upon generations until all Japanese honey bee colonies have the bee balling behavour. One way this could happen sooner is if the hornets are especially efficient and wipe out ALL colonies with no bee balling behaviour, leaving only the few bee ballers to survive non-hornet threats and fill up the population.

A long series of lucky breaks. But go all the way back to the start… How did the complex bee balling behaviour itself evolve in the first place?

It’s not a simple matter to coordinate letting the hornet in, jumping a hornet simultaneously, and vibrating instead of stinging. Especially when the hornet can whack 40 bees per minute – no teamwork by the bees means death.

Seems a very far cry from standard bee behaviour to me. Was it merely random chance that a non-productive behaviour was not weeded out by evolution before it turned out to be a beneficial tactic against hornets?

It’s very easy to say: “The Japanese honey bees evolved the bee balling behaviour as a defense against hornet attacks.” But such a proclamation says nothing about WHERE the behaviour originated from or HOW it reached the point of usefulness from a nonsense behaviour.

Genes don’t just spontaneously appear from nowhere, as Lamarckian evolution has been disproven.

All together, a host of assumptions and fortunate happenstances are required for bee balling to evolve by random chance. Similar to the extremely complex behaviour of building 6 metre high termite mounds with excellent air conditioning.

PS. Interestingly, linked to by a Biology module.

Tags: Asian hornet, bee ball, thermal defense