Do Insects Sleep?

Fruit fly.
Fruit flies exhibit sleep-like behavior, according to several studies. Getty Images/Oxford Scientific

Sleep restores and rejuvenates. Without it, our minds aren't as sharp, and our reflexes become dull. Scientists know for sure that birds, reptiles, and other mammals experience brain wave patterns similar to our own during periods of rest. But what about insects? Do bugs sleep?

It's not quite as easy for us to tell whether insects sleep the way we do. They don't have eyelids, for one thing, so you'll never see a bug close its eyes for a quick nap.

Scientists haven't found a way to study insect brain activity, as they have in other animals, to see if typical rest patterns occur. 

Studies of Bugs and Sleep

Scientists have studied insects in what appears to be a resting state, and have found some interesting parallels between human sleep and insect rest.

In a study of fruit flies (Drosophila melanogaster), researchers videotaped and observed individual fruit flies to determine whether they slept. The study authors reported that the insects exhibited behaviors that suggested a sleep-like state. At a particular time in the circadian day, the fruit flies would retreat to their preferred napping locations and get comfortable. The insects would remain still for over 2.5 hours, although the scientists noted the flies would sometimes twitch their legs or probosces while at rest. During this period of rest, the fruit flies didn't respond easily to sensory stimuli.

In other words, once the fruit flies were snoozing, the researchers had a tough time waking them up.

Another study found that usually diurnal fruit flies with a certain gene mutation would become active at night, due to increased dopamine signals. The researchers noted this change to nocturnal behavior in fruit flies is similar to that seen in humans with dementia.

In dementia patients, an increase in dopamine can cause agitated behavior in the evening, a symptom known as sundowning. 

Studies have also shown that insects deprived of rest suffer much like people do. Fruit flies kept awake beyond their normal active period would recover the lost sleep by napping longer than usual when finally allowed to rest. And in one study population that was denied sleep for an extended period of time, the results were dramatic – about one third of the fruit flies died.

In a study of sleep-deprived honey bees, the insomniac bees could no longer perform an effective waggle dance to communicate with their colony mates.

How Bugs Sleep

So, by most accounts, the answer is yes, insects do sleep. Insects clearly rest at times, and are aroused only by strong stimuli – the heat of day, the darkness of night, or perhaps a sudden attack by a predator. This state of deep rest is called torpor, and is the closest behavior to true sleep that bugs exhibit.

Migrating monarchs fly by day, and gather for large butterfly slumber parties as night falls. These sleep aggregations keep individual butterflies safe from predators while resting from the long day's travels. Some bees have peculiar sleep habits.

Certain members of the family Apidae will spend the night suspended by only the grip of their jaws on a favorite plant.

Torpor also helps some insects adapt to life threatening environmental conditions. The New Zealand weta lives at high elevations where nighttime temperatures get quite icy. To combat the cold, the weta simply goes to sleep at night, and literally freezes. In the morning, it thaws out and resumes its activity. Many other insects seem to take a quick nap when threatened – think of the pillbugs that roll themselves into balls the moment you touch them.

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