Do Insects Sleep? (asked by Claire)
In my recent article in Experimentation magazine, I made the rather bold claim that all animals sleep in some way or another. This is certainly true for all mammals and probably all vertebrates, but do insects experience sleep, and how similar is their experience to ours?
In order to determine whether insects can be said to sleep, we first have to define exactly what we mean by sleep. Traditionally, sleep is defined as a “rapidly reversible state of immobility and greatly reduced sensory responsiveness” (Seigel, 2008). It is distinct from simply resting, where we are still conscious. It is also distinct from more permanent states of rest such as hibernation. Sleep in humans, and in mammals in general, is defined by specific patterns of electrical activity in the brain, but can the same patterns be found in insects?
Rest behaviour including reduced responsiveness has been shown in cockroaches, bees and scorpions. Not many people have been looking, though! Some studies have reported that rest deprived cock roaches will compensate during their next period of rest, a key characteristic of mammalian sleep. Cockroaches have been shown to ‘sleep’ for around 14 hours a day, and in this state they are significantly less reactive to outside stimuli. Specific sleep ‘postures’ associated with reduced responsiveness have been found in many invertebrates including moths, sea slugs and beetles. In fruit flies, a rest state exists which fulfils all criteria for defining sleep in humans.
In even more distantly removed branches of the tree of life, there have been no claims so far for sleep in single celled organisms. There is clear evidence, however, for circadian activity rhythms in a variety of simple organisms including cyanobacteria, protists and dinoflagellates.
So, it looks like everything rests, but whether all animals sleep really depends on how you define sleep. If sleep in mammals is important in brain function then some or even all aspects of sleep may be unnecessary for organisms with less complex brains. Certainly for invertebrates which lack brains entirely, such as sponges or jelly fish, sleep, as we know it, seems very unlikely. When it comes to insect research, most people tend to lose interest when the animal ceases activity. It may be a long time before we really understand the processes of sleep in invertebrates.
Want to know more?
- Campbell and Tobler (1984) Animal Sleep: A Review of Sleep Duration Across Phylogeny, Neuroscience & Biobehavioral Reviews 8, 269-300
- Rau and Rau (1916). The sleep of insects. An ecological study. Ann Ent Soc Am 9 227-274
- Sharplin (1963). Choice of resting site by noctuoidea (Lepidoptera). Ent Mon Mag 99: 53-62
- Siegel (2008) Do all animals sleep? Trends in Neurosciences 31, 208 – 213
- Strumwasser (1971). The cellular basis of behavior in Aplysia. J Psychiatr Res 8: 237-257
- Young (1935). Sleep aggregations of the beetle, Altica Bimarginata. Science 81: 435-439
Featured image is used under a creative commons license from Wikimedia commons. Original image by Aka.