Anyone with even the slightest fear of creepy crawlies has probably been in the following situation. You settle down for the evening and quick as a flash you see a behemoth of a spider run out. It dashes underneath the sofa before you can react, and, your night ruined, you are left waiting for it to kill you. After a while you’ll convince yourself that it has probably gone to sleep and, seeing as it’s 2am, you should too. However, did it go to sleep? Do insects sleep at all?
One of the many questions which I get when I tell people that I study sleep is some variant of: do insects sleep? What is the smallest creature that sleeps? Do you sleep? Well let’s delve into the world of the mini-beasts to find out the answer to that first one.
Many insects such as bees, moths, cockroaches, and butterflies (to name but a few) will show behaviours that seem indicative of sleep: relative immobility, increased arousal threshold (e.g. harder to wake them up), and drooping antennae. Insects don’t have eyelids so they can’t get “shut-eye” in the usual sense but these other behaviours look a lot like sleep. However, is this really sleeping? Some have argued that the pattern of inactivity shown by some insects can be better referred to as torpor. This is like sleep but torpor involves enhancing the survival of the organism during times of limited resources or when in a harsh environment (e.g. low temperatures during winter). Torpor is often compared to hibernation in mammals and referred to as a ‘mini hibernation’. Unlike sleep, torpor is regulated by external factors rather than an internal clock as in humans and other mammals. However, if what we see is simply torpor in insects then we would not expect them to experience difficulties in functioning after sleep deprivation. So, do insects show signs of poor functioning if they don’t sleep even during normal environmental conditions?
The science suggests that they do.
For example, fruit flies show patterns of inactivity remarkably similar to human sleep – they show recovery sleep, struggle with vigilance and performance after not getting enough rest, and show a steady rhythm of wake and sleep. One well researched example of the effects of sleep loss on bugs can be seen in honey bees. As they mature into foragers for a hive they move from near constant activity to strongly structured patterns of activity and rest as they hunt for food. However, when foragers are not able to sleep they show difficulties in successfully carrying out vital tasks – for example, dancing. For bees, dancing is a vitally important skill (honestly). While away from the hive bees can communicate with one another through a display known as the ‘waggle dance’. This figure of eight movement, interspersed with a slight waggle, is meant to tell other bees about the distance and direction of food sources, pollen, and the hive. Now, how exactly do you deprive a bee of sleep without interfering with its daily schedule? I’m glad you asked. You use something aptly named the ‘Insominator’.
This fantastically named device is a beautiful example of the awful sense of humour scientists possess. The device was developed with the express purpose of ensuring that bees were sleep deprived in an automatic manner while still being part of their hive. Like humans, research should try not to interfere with the daily schedule of participants (no matter how many legs they have) so we can be more confident it was the thing we’re interested in, and manipulated in some way, which is responsible for the effects observed. Despite its funny name, it was actually a pretty cool piece of kit and allowed the bees to go about their social activities (bees are rather social) whilst only disrupting their sleep.
In the study led by Prof. Bennett Klein, they compared the performance of bees’ waggle dance before and following sleep deprivation. Interestingly, when the bees were kept awake they were less able to effectively carry out the waggle dance and alert other bees to resources. More specifically, the bees were less accurate in conveying direction information to other bees and this in turn, it is predicted, would negatively impact foraging behaviour of other bees in the hive. As is seen in other social creatures, and me without a strong coffee or five, sleep deprivation impaired communication skills of these honey bees. Although the mechanisms are more complex in humans it suggests that certain insects do sleep and that this can have a negative impact on social functioning. Although the jury is still out as to whether the rest shown by many insects constitutes sleep, the effects of a lack of this inactivity seem to mimic the effects seen in humans. At this point, I’ll let you make the decision whether we can call this sleep or not. Alternatively, if you have any ideas on how to study whether an insect sleeps, please send your answers in on a postcard addressed to Jack and marked ‘SCIENCE’.
So, if anyone asks you whether insects sleep you can go forth and spread the unclear, slightly contentious, word. Alternatively, you can just remember that bees dance, scientists have a terrible sense of humour, and that the spider still underneath your sofa is asleep. Probably. In fact, it’s probably best just to seal off that room.
Klein, B. A., Klein, A., Wray, M. K., Mueller, U. G., & Seeley, T. D. (2010). Sleep deprivation impairs precision of waggle dance signaling in honey bees. Proceedings of the National Academy of Sciences, 107(52), 22705-22709.