MANITOULIN—Have you ever wondered if insects such as bumblebees can fly from flower to flower all day without taking a break? Turns out they can’t and indeed, like most other insects, they need to periodically take a nap.
But do insects sleep? The answer appears to be ‘sort of.’ It is known that insects alternate between periods of alertness and rest similar to humans and other animals, but it is not clear if they sleep the same way as humans and other animals.
Scientists study sleep in large animals by observing brain activity. This can’t be done in the same way with insects because they are so small. However, it has been proven that insects need to periodically sleep. They just do it a little differently than humans.
Sleep is a fascinating behavioural state for which much remains to be learned. Different animals require varying amounts of sleep to meet their needs. Humans spend about one-third of their lives sleeping, whereas other animals such as bats, beavers and chipmunks spend half their lives sleeping. Short sleepers like horses, cattle and sheep have sleep periods of 3-5 hours over a 24-hour period.
Sleep is a state of rest which allows animals to alter various physiological processes to conserve energy, allow muscles to recuperate from exertion and undertake various physiological functions. Without sleep, reflexes become dull and decisions aren’t as sharp.
It’s not as easy to tell whether insects sleep the way we do as they don’t have eyelids, so we can’t see them close their eyes for a quick nap. Scientists haven’t found a way to study brain activity in insects, as they have in other animals, but by most accounts, it appears that insects sleep, or at least take rests or naps. They are then aroused by strong stimuli such as change in temperature, levels of light at dusk or dawn, or attack by a predator.
Sleeping is particularly important for insects such as bees as it is for us as it plays an important role in memory acquisition and retention.
I recently saw a bumblebee in our garden near Sheguiandah in mid afternoon with its head pressed into the base of petals in a rose flower. At first, I thought it was dead or damaged as it didn’t move. I carefully removed the flower with the bee inside sat down with it so I could get a better look.
I gently stroked the back of the bee with my finger, and to my surprise, it slowly began to move its antennae and legs and stretch similar to us when waking up in the morning. It even extended and contracted its mouth parts as if it was yawning.
The bee began vibrating its wing muscles, then after a few moments, it lifted into the air. It didn’t immediately fly away but took a few tight turns around my head as if to check out the huge monster who had rudely awoken it from its nap.
Rest is necessary for insects to remain alert during their waking hours. The more sleep an insect gets, the longer it lives. Increased alertness helps insects avoid predators and search for food with better precision. Without rest, they do not forage as well and may lay eggs on the wrong plants.
When insects and other animals enter a sleep state, they become partially disconnected from the external world, owing to reduced sensory activity. During sleep, animals cannot forage or take care of their young. Nor can they escape from life-threatening dangers such as predators.
While insects may not physically get some ‘shuteye,’ since they do not have eyelids, they enter a state of metabolic rest called ‘torpor’ where they exhibit decreased physiological activity such as lower body temperature and a lower metabolic rate.
During torpor, insects may even assume a preferred sleeping position just like some people prefer to sleep on their sides and some dogs on their backs. While asleep, their eyes do not respond to moving images the way they would during the day when they are awake.
Where do insects rest when they are in a state of torpor? Resting spots can be just about anywhere they feel comfortable and safe from predators such as under dead leaves or rocks on the ground. Some bees spend the night on a plant stem, holding on with just their mouthparts.
Most insects are either active only during the day or at night. When they’re not active, they rest. Migrating monarch butterflies, for example, fly by day, but gather in large butterfly slumber parties in trees as night falls. These sleep aggregations keep individual butterflies still and safe from predators while resting from the long day’s travels.
However, scientists have established that these sleep-like states are also important for insect cognitive function. One of the most studied insects in this area is the common fruit fly – the small fly with red eyes one sees flitting around the fruit section at your grocery store.
Researchers have discovered that fruit flies alternate between sleep-like states lasting about three hours and periods of alertness. During these rest periods, fruit flies are relatively unresponsive to external stimuli and droop their antennae.
Fruit flies divide each day into periods of naps then sleep longer at night. Depriving them of rest causes cognitive problems such as learning certain tasks. Fruit flies deprived of rest for long periods will die.
Well-studied insects such as honeybees take naps during foraging excursions, as apparently did the bumblebee described in this article. When bees sleep, their antennae droop, their head and tail tuck in, and their wings rest on their bodies.
Honeybees sleep 5-8 hours a day, and like us, they sleep at night. Sleep deprived honeybees cannot effectively communicate with their hive and have trouble navigating.
Honeybees snuggle up at night and hold each other’s feet. This likely prevents them from falling within their hives. It also helps them share the heat of their bodies and provides social cohesion, protection and communication within the colony.
Although all bugs sleep it doesn’t mean they will go to bed for eight hours as does the average human. The sleep cycles of insects will also differ according to their needs. For example, caterpillars of monarch butterflies will have different sleeping patterns than the adults.
As to whether or not insects dream, and what they dream about, we can only guess. Perhaps butterflies dream about warm sunny days in fields full of flowers and plants on which to lay their eggs, while others may have nightmares about entomologists chasing them with a net!
by Joe D. Shorthouse
Dr. Joe Shorthouse is a retired entomology professor at Laurentian University who spends his summers near Sheguiandah.
