How can you tell an insect is sleeping?

I’ve recently come across pictures on websites that showed one dragonfly and a bee sleeping. Not together, I mean different pictures and different websites (I think). The pictures looked like they had been taken during the day. Insects don’t have eyelids, so how did the photographers know they were sleeping?

There are several paper wasp nests near my place. One evening after dark I happened to be shining the light of my phone onto one, and the wasps were obviously sleeping because no one stirred. At first at least. They did eventually wake up, because I took a few pictures to determine the species. My impression was they were as startled as I would be if someone shone a light into my face while I was sleeping. But while they were still asleep they didn’t look any different than during the day.

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I think that a reduction of sensitivity to stimuli and reduced motion are the more important “tells”. Someone else may know more.

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I’ve had the pleasure to personally observe a dragonfly at night (see link for the observation).

Anyone who has observed dragonflies during the day will know that they rarely stay still for long. The dragonfly I observed at night (during this year’s City Nature Challenge) was utterly motionless, and did not react at all to the light of the torches my group held; there was not an iota of movement in its body or wings. It looked for all the world like a beautiful ornament that nature had made and placed on the branch for us to behold.

It was a moment of awe for me, as I gained for myself a deeply intimate look at the otherwise hidden aspect of a dragonfly that I wouldn’t have seen otherwise.

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I once found several bees sleeping, hanging by their jaws from a flower stalk together early in the morning. It’s a funny thing to see but apparently a lot of them do it. I’m sure there are plenty of photos online of this. I’d hate to have to spend the night clinging to my bed with my teeth. :grin:

edited to add: In answer to your question, I think @trh_blue covered it but I wouldn’t be surprised if there were more family- or order-specific clues.

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Many taxa retract their antennae when sleeping but hold them erect when awake-but-motionless. Some taxa may also assume a folded or less erect posture when asleep.

Note that while diurnal insect taxa tend to be always asleep at night many nocturnal ones are awake to some degree during the day. For example, I have observed that the large katydid Scudderia mexicana frequently feeds during the day, although it is bolder at night.

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I also hasten to add that for some mysterious reason many insects are highly unresponsive to external stimuli whether awake or asleep; S. mexicana does not cease singing or flee when approached, exposed to loud sounds, or even when a flashlight is shone into its face. It only exhibits alarm behavior when poked or when exposed to suspicious airborne/substrate vibrations (it will not flee from wind, but if its branch is artificially shaken, a hand fans air at it, or if it is blown on, it will panic).

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Oh, good. I thought we were on the verge of a scandal.

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Not the same as sleeping, but I’ve seen dragonflies (Libellula, Tramea) that were perched and torpid, either in very cool weather in the morning or following an afternoon thunderstorm that caused temperatures to plummet. They were unresponsive when prodded and positioned partly within a shrub and not in a more typical open and exposed perch as they would be during the day when active.

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Thank you all for your feedback and links. Much appreciated.
Looks like I am hooked on this subject now. Has anyone seen this post:
https://forum.inaturalist.org/t/why-was-this-xylocopa-bee-so-fixated-on-one-place/24263/5

In a hot climate it makes sense (to me) to be keeping still and rest during the hot hours of the day. I keep seeing flies (that would normally be taking off very fast) resting (sleeping?) very prominenty on an exposed leaf in the shade, letting me move around them taking pictures. I guess it’s safe to assume that they, too, prefer to conserve energy (and humidity) when it’s so hot.

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Yes, that antenna posture I have noticed in some beetles; those with very long antennae that wouldn’t budge or take off with me around held them aligned along their body.

That clinging to a stalk was in fact shown in the bee pictures I saw. :-)

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Tonight I was out with the dogs at dusk, and ended up in a moth dormitory. ;-)
While one nine-spotted moth was already asleep:
https://www.inaturalist.org/observations/85021299
another one nearby was still punching its pillow:
https://www.inaturalist.org/observations/85022135

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All right, I may perhaps now seem obsessed with sleeping insects. Discussing this with a friend who is a beekeeper, we veered into kept bees. In the event someone here might also be interested, this page here covers sleeping honeybees:
https://beehivehero.com/do-bees-sleep/
Inter alia, it has a link to this 2008 research paper (available for free, downloadable also as PDF):
https://journals.biologists.com/jeb/article/211/18/3028/17673/Caste-dependent-sleep-of-worker-honey-bees

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Check out this project by @zportman for more sleepy bee slumber parties!

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Thanks for the pointer! Fascinating.
Bees can sleep in pretty weird positions – like cats. ;-)

Took photos of a couple Bombus that went to “bed” early, while many more were still out drinking. They tucked into the branch, and weren’t out on the flowers. They did not move. Not sure about thee antennae, but good to know and will check in the future.

On a hot day in the summer, I saw Bombus males clinging to the inside shady side of my parent’s porch or hanging below flowers (like below an umbrella). They seemed to be having an afternoon siesta.

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Bees will hang onto flowers when it’s windy, too.

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