Pushing out some Zs!
Every hard-working animal deserves some rest, but do bees sleep? Perhaps it seems obvious that the answer is a resounding ‘yes’, but positive confirmation was not obtained until the 1980s, through the observations of researcher, Walter Kaiser. In what was the first record of sleep in an invertebrate, he discovered that honey bees sleep for an average of five to eight hours per night. Just as mammals and other animals adopt a relaxed pose when sleeping, bees’ antennae become inert and droop downwards, and their legs flex, folding underneath and allowing heads and bodies to drop, while the wings rest on the body. Sometimes, sleepy bees may even topple over sideways! Scientists have also found that, like humans and other animals, bees undergo various different phases of sleep, which coincide with distinct patterns in the brain. The body temperature of sleeping bees is also lower than when they are active – which again parallels humans.
Predictably, forager honey bees sleep at night, when they are unable to navigate accurately to collect nectar and pollen. Sleeping foragers are typically located at the perimeter of the nest or hive. Younger workers, whose duties are confined to the maintenance of the nest, do not have a defined sleep pattern and may be active at any time of the day or night. They usually slumber closer to the centre of the colony. Bees have also been observed to sleep in flowers, or upon grass stalks. Again, like many other animals, including humans, the first item on the agenda for honey bees when they wake up is their toilet – and they immediately set about grooming themselves.
Sleep has been documented amongst almost all animals, including simpler life forms such as nematodes. It has both physiological and behavioural elements, and is broadly defined by a state of reversible unconsciousness in which there is a lack of responsiveness to external stimuli, characteristic brainwave patterns, sporadic eye movement, reduced metabolism, and a relaxed posture in which there is a loss of muscle tone. It is usually repeated in a 24-hour cycle. Sleep appears to be a necessary phenomenon; sleeping animals are typically vulnerable so there must be considerable benefits to be derived from this process, although these are as yet poorly understood. Sleep does enable brain glycogen levels to be restored (these drop during waking hours) and in the case of diurnal animals, assists to conserve energy during the coldest part of the day.
Scientists have found that humans who do not receive adequate sleep fall into a situation of ‘sleep debt’ in which cognitive processes, reaction times and motor functions are impacted. Sleep-deprived rats will exhibit weight loss (in spite of increased food intake) and other symptoms consistent with impaired immune function, and if completely deprived of sleep will eventually die within weeks. Similarly, honey bees deprived of sleep have difficulty finding their way home and cannot effectively perform the waggle dance, in addition to exhibiting other signs of fatigue.
Interestingly, some birds and aquatic mammals, such as whales, employ a strategy known as ‘unihemispherism’, in which only one cerebral hemisphere sleeps at a time. This enables the animals to remain alert to threats, as well as to surface periodically to breathe air. Some sharks, including great whites, must swim continually to ensure a steady stream of water over their gills, and it is speculated that they too may use unihemispheric sleep, although this remains to be proven in fish. Unihemispherism has been advanced in support of the argument that no animal can do without sleep altogether.
Bumblebees survive the rigours of winter by hibernation. This is a state of torpor that enables them to conserve energy. Hibernation greatly reduces the need for sleep, but does not erase it entirely; sometimes animals will terminate their hibernation just so they can go to sleep!