Sleepy Bees Waggle Sloppy

For humans, sleep deprivation has a negative impact on performance in many areas, such as motor and communication skills. In particular, communication impairment is the topic of an article published yesterday in PNASProceedings of the National Academy of Sciences. But the research in this paper isn’t about humans – it’s about honeybees.

To begin with… bees sleep?  Apparently so.  Bees don’t have tiny little eyelids that droop, nor do they snore.  Instead, bee sleep is characterized by certain changes in their behavior that can be observed by interested researchers.  The bees stop moving, they have a “specific posture” (?), and they become less responsive to disturbances.  Most of this sleep happens at night.

So what happens when you don’t let a bee get her beauty sleep?  Well, she gets sloppy.

One way that bees communicate with each other is by a dance called a “waggle dance”. They go out foraging for food, and then they come back to the hive and tell the others what they saw through interpretive dance.  The dance consists of various waggles and turns in certain sequences and with certain body angles.  Precision is important to accurately convey the direction of and distance to food, but sleepy bees get careless with their body angles and thus communicate less effectively.

How exactly does one go about measuring a bee’s sleep deprivation?  Researchers set up a bee hive in a shed and tagged several of the bees with either a tiny piece of steel or a tiny piece of copper.  All of these lucky tagged bees were taught to visit a sugar-water feeder about 1 km away from the bee hive.   The researchers then used an “insominator” – a rigged-up apparatus consisting primarily of magnets – to disrupt the sleep of the steel-tagged bees at night.  This magnetic apparatus swept back and forth across the bee hive; as it passed over bees with steel tags, the attraction between the steel and the magnets tugged or pushed on the bees, giving them a little jolt.  The copper-tagged bees served as controls – their tags were unresponsive to the magnets, and so they were able to sleep uninterrupted by the sweeping magnets.  All the rest of the untagged bees in the hive were also unaffected by the insominator.

Bee Hoverfly Waggle Dance (Wikimedia Commons) see link in comments for diagram of actual honey bee dance

The next morning, following a night of tossing-and-turning (for the steel-tagged bees at least), the bees went out foraging as usual.  As usual, they returned to the hive later and reported their findings by waggle dancing.  The dance of the copper-tagged bees looked the same as ever, but the dance of the steel-tagged bees was a bit messier.  They did the right sequences of turns and pauses and waggles, but they didn’t do their body angles very well.  Apparently, body angles convey information about direction (north, south, etc.), so faulty body angles could send the other bees off on the wrong path.

This seems to be the first study ever to look at how sleep deprivation affects communication by non-humans.  I’d like to see more studies like this – maybe whale songs would be off-key when they’re behind on their sleep?  Or tired parrots might slur their speech when asking for a cracker?

Citation:
Barrett A. Klein, Arno Klein, Margaret K. Wray, Ulrich G. Mueller, Thomas D. Seeley (2010). Sleep deprivation impairs precision of waggle dance signaling in honey bees Proceedings of the National Academy of Sciences : 10.1073/pnas.1009439108