Do insects sleep? The shortest answer to this question is yes, but not all insects sleep the same.
In fact, we can start with the Britannica definition of sleep: “A normal, reversible, repetitive reduced responsiveness to external stimuli, accompanied by complex and predictable changes in physiology…”
Sleep state in insects first came into focus in 2000 with research on fruit flies by Popular Science. Two separate research groups have found that some sleeping flies are more difficult to scare away than awake flies.
This also applies to slumbering insects such as cockroaches, praying mantises and bees. These insects fall by gravity while they sleep and have an increased arousal threshold. Cutely, cockroaches fold their antennae inward during sleep as a way to protect their sensitive sense organs.
Insects have a central nervous system, a key feature for dormant organisms. Insects also exhibit a sleep and wake pattern and a circadian rhythm, although the nature of this pattern varies depending on the species.
The existence of an internal circadian order was first discovered in the cockroach Leucophaea maderae. The cellular origins of this pattern were then traced until the researchers were able to alter a cockroach’s circadian rhythm by transplanting a specific part of the brain from a different cockroach trained to a different sleep-wake cycle.
The circadian rhythms of foraging species such as honey bees, their tendency to be busy during the day and rest at night, are striking. During rest, honey bees move less, muscle tone decreases, response threshold rises, body temperature decreases. And these represent the four basic characteristics of sleep, just as in mammals and birds.
Fruit flies are also known to exhibit a trait called “sleep rebound”, in which deprivation leads to a greater need for sleep. Studies have found that sleepless flies sleep more than their well-rested companions.
Proving the absence of sleep is a complex task, but there are bugs for which sleep has not yet been proven. For example, butterflies are known to rest. But “we don’t know if they’re asleep,” Katy Prudic, a biologist at Oregon State University, tells National Geographic.
What we do know is that butterflies are one of the few insects that stop moving in very cold weather, and this is a protective state known as dormancy, unlike sleep. Insects also hibernate as a way to survive the winter, this is something seen in ladybug species.
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