It wasn’t that long ago that a researcher named Walter Kaiser discovered that honey bees do, in fact, sleep. In 1983, he observed changes in body posture that indicated forager bees were moving from an awake state to one of sleep.
Specifically, Kaiser saw that the forager bees had reduced muscle tone, decreased motility, lower body temperatures, and required more stimuli at a higher threshold to become alert. Since these characteristics closely resembled those of humans, mammals, and birds while sleeping, he came to the conclusion that what he was observing was indeed sleep among the honey bees in his study.
Why Do Bees Sleep?
Although sleep is important for all of the different worker castes in the hive, it may be most crucial for the foragers. A colony will collapse if food is not available, and the foragers are the workers responsible for flying out of the hive and bringing nectar and pollen back in.
Simply put, if foragers do not get enough sleep – the kind of sleep that helps them work at their peak when among the flowers – it could be devastating for the colony.
Without sleep, foragers’ communication skills are impaired, and they need to be excellent communicators in order to signal to others where the best food resources are located. If foragers are sleep-deprived, the waggle dance they do to map out a floral route may fail to provide correct information, and the other foragers could waste valuable energy on a trip that doesn’t lead them in the right direction.
And once the bees are done extracting pollen and nectar, they must find their way home. Sleep deprivation can cause bees to get lost as they try to use landmarks to reorient themselves for the trip back to the hive. With regular sleep, knowing the way home should be second-nature to foragers, but if they don’t get enough sleep, they’ll start to forget the things that used to come easily to them.
Deep sleep is especially important to foragers. While in this state, memories are formed using images from the day’s activities. Deep sleep will help to convert fleeting memories into more permanent ones that can be used for foraging in the future.
Of course, sleep is also essential for the other workers in the hive, as they need rest to be efficient and productive, as well. A bee colony is a superorganism – a system that relies on all of the bees in the hive for survival. If any of the castes – cleaners, nurses, guards, etc – fail to do their jobs well, the colony can die.
How Do Honey Bees Sleep?
There are two ways to characterize how honey bees sleep. The first is to describe their physical posture while sleeping and the second is to talk about the quality of their sleep, especially as it relates to the difference between younger and older bees.
As scientists observe sleeping bees, they notice several commonalities among all of the slumbering honey bees. The antennae droop down, as does the upper body and the abdomen, and their wings rest against their bodies. Some bees fold their legs beneath their bodies, and other bees may hold each other’s legs while sleeping.
As bees approach a deeper sleep state, they become more relaxed and lose muscle tone. Keeping the antennae immobile for long periods of time may also suggest that the bee is in a deep sleep state.
As for sleep patterns according to age, one study noticed that bees as young as three days old slept as deeply as did the older foragers. In both age groups, sleep moved downward from a light/medium sleep to a deeper state.
But there was a difference in the way the young bees moved back and forth between the different sleep states. Young bees that looked like they were about to wake up would suddenly fall back into a deep sleep. When they did finally wake they might end up taking another nap just hours after rousing.
By contrast, foragers – who are the older bees – wake from a deep sleep and immediately become conscious. Once the foragers wake up, they will be active until their day’s work is over – around sunset. Older bees exhibit a more well-defined sleep pattern than do younger bees.
When Do Bees Sleep?
When bees sleep is dependent on their assigned role within the colony. In the honey bee hierarchy, queens have the most important role – that of reproducing. The only job a male drone has is to mate with the queen. But the remaining female bees are the ones who have the most work to do. These females can be split into two distinct groups: the house bees and the foraging bees.
House bee activities include:
|Bee Cleaner||Their sole job is to remove dust, debris, and hairs from the other worker bees, and they must do this job quickly, as if they were in an assembly line.|
|Hive Cleaner||They’re the bees that get rid of used cells and generally clear any debris out of the hive.|
|Maintenance||These bees repair cracks in the hive using propolis.|
|Undertaker||The majority of bees die outside of the hive, but the ones that do die inside must be taken outside to dry. The undertakers then fly these dried bees far away from the hive so that they won’t attract pests.|
|Queen attendant||These bees serve at the pleasure of the queen, and must groom and feed her.|
|Nurses||They feed and take care of the developing larvae.|
|Comb Builder||These are bees who secrete beeswax that is the building block of honeycomb. It often takes hundreds of bees to build just a small section of comb.|
|Ripeners||These bees deposit nectar into the comb cells and fan it to allow the water to evaporate.|
|Pollen Packers||Foragers hand over the pollen they’ve collected to the pollen packers, who deposit it into the cells.|
|Cappers||These bees use secreted beeswax to cap cells containing honey and pupae.|
Foraging Bee Activities:
|Nectar and Pollen Collectors||These bees forage for pollen and nectar that is then returned to the colony for the queen and the young.|
|Propolis Collectors||They remove it from trees and carry it back in their pollen baskets.|
|Water Collectors||Only 1% of the bees are tasked with this job, even though water plays an important role in cooling the hive and diluting raw honey for larvae.|
|Guard||These are the hive “bouncers” who keep intruders away. They’ll sting and emit a pheromone to warn the bees inside of the hive.|
House bees are younger bees, and due to their caretaking responsibilities, they have a much longer workday than do foragers. Since they are active both day and night, they sleep whenever they can over a 24-hour period.
Foragers, by contrast, do most of their sleeping during the nighttime hours and will take longer naps than the younger house bees. Research has shown that foragers do sleep mostly at night and that their deep sleep occurs more often at night than during the day.
Where Do Bees Sleep?
Where honey bees sleep in the hive has to do with their particular caste or role in the colony’s society. As mentioned above, the younger bees start out by tending the hive and progress through a chronological sequence that begins with cleaning, moves on to care-taking, and later to food receivers and storers. The next step in their progression is the role of forager, and these bees are older, having spent their youth doing “house bee” jobs.
The location of each job – and the amount of time it takes to do that job – correlates with where bees will do their sleeping. The young house bees will sleep closer to the centre of the nest, near the developing brood and in the areas where they may need to deal with cells that store honey and larvae.
Younger bees can also be found sleeping inside cells. It’s primarily the cell cleaners – the lowest caste in the hierarchy – that sleep inside cells, and as each caste progresses, there are fewer bees sleeping in cells.
Older worker bees – the foragers – sleep outside cells and nearer to the perimeter of the nest. It’s thought that the noise and activity nearer the centre of the hive make it more difficult for foragers to get the restful, energy-restoring sleep they need for a demanding day of foraging when they wake. Sleeping near the perimeter allows foragers to rest mostly undisturbed and to get better quality sleep.
How Long Do Bees Sleep per Day?
In cumulative hours, honey bees sleep between five and eight hours a day, similar to the number of hours humans sleep.
But unlike humans, who tend to sleep in one continuous stretch, honey bees take several “naps” within a 24-hour period. The timing of these naps depends on which caste the bees belong to, but it’s estimated that forager bees (the most elevated caste and the oldest bees in the colony) take around 50 naps and that younger bees take about 40 naps.
Why Do Foragers Sleep Primarily During the Night?
Foraging is a job that typically takes place during the day – although there are a few species of bees that do forage at night. Most flowers are open during the day and a bee’s vision is at its best during daylight hours. You could say that foragers have “office hours” and must do their jobs when the business is “open.”
Because foragers must work during a set number of hours during periods of daylight – and since so much energy must be expended doing foraging tasks – it makes sense that they would get most of their sleep during the night when flowers close up and they must restore their energy for the following working day.
Does the Body Temperature of Bees Drop When They Sleep?
When bees sleep, their body temperature adjusts to that of their surroundings, which is lower than their average body temperature while awake. Their temperatures will not rise again until they begin to activate their flight muscles. Because each worker caste is located in a particular part of the hive to do its job, temperatures will vary depending on where the bee is situated.
Cell cleaners tend to sleep in warmer areas, and this may increase their neural development, helping them to consolidate memories. The youngest bees may sleep in the warmest regions (near the brood) because at this temperature they are able to better develop their flight muscles.
Food storers tend to sleep in colder areas, and like foragers, this may help conserve energy for the demanding activities assigned to them.
There is also evidence to support the theory that foragers choose cool areas of the hive – but not too cold. Finding the perfect temperature balance works to conserve energy as well as activate the regenerative processes of sleep.
Foragers are colder either in light or deep sleep versus their temperatures when awake, and food storers show a notable difference in temperature (cooler) when they’re in a deep state of sleep. Nurses, however, do not show any significant temperature difference, whether awake or asleep.
Do Bees Wake Up to Light?
Much like with humans, if a bee is in a deep state of sleep it’s difficult to wake it. Bees are naturally awakened as darkness ends and the sun rises higher in the sky. To find out if there are other stimuli that serve to wake the hive a university research team placed video cameras and accelerometers inside a beehive to record what’s known as “Dorso-Ventral Abdominal Vibration.”
This vibration, caused by rapid bee movement either on the comb or on another bee, serves as a signal to the foragers to get up and become active. Scientists used light as a stimulus and found that honey bees in a deeper state of sleep required a more intense light source to respond and wake than bees in a lighter sleep stage.
Honey Bee Sleep Versus Human Sleep
Although honey bees don’t mirror the exact sleep patterns of humans, there are many similarities. Like honey bees, humans tend to sleep at night so we can have the energy to do their demanding jobs during the day. Both human’s and bee’s body temperatures decrease during sleep, they move less, and it is more difficult to wake them when they are in a deep sleep stage.