Yes, kind of.
Here’s a collection of images of some ‘sleeping butterflies’ I’ve come across in Tambopata.
In general, there are a few common traits for this nighttime behavior. They almost always ‘sleep’ hanging upside-down and underneath a leaf. This hanging requires minimal energy, as their tarsi (aka ‘claws’) can grasp on to the leaf with little effort, opposed to standing right side up.
Why under a leaf?
Two main reasons. For one, they gain protection from rain that often falls at night. Secondly, they are more hidden from early-rising birds looking for a meal that may be active before the butterflies are warm enough to take off.
I have often noted that butterflies with warning coloration (black and bright yellow, orange wings) sleep more exposed, for example under a thin twig rather than under a covering leaf. This coloration is there as a signal to warn birds that they may be poisonous to eat. So, it may work to the butterflies’ advantage to show their entire color signal (aka wings) to birds, rather than keep their wings partially hidden under a leaf, explaining why they may tend to sleep more in the open.
So, are they actually asleep?
Depends on your definition of sleep. If you want to define sleep as an inactive, low metabolic state: yes. This low metabolic state is often driven by the temperature in the air itself; ectothermic butterflies require outside heat-energy to become active.
There’s really no use in being active at night for most butterflies- they can’t see each other to mate, and empty flowers are restocking themselves with nectar for the following day. So, it makes sense that they would go into this ‘sleep’ state which likely helps them digest the day’s feed, produce eggs/sperm, and basically take advantage of a time in which there is nothing better to do.
During this nocturnal state they are still capable of flying off if disturbed. Also, there are some butterflies that specialize in roosting together at night in groups, and others I’ve seen regularly in pairs. Some butterflies in temperate climates are capable of overwintering as an adult, which is basically a physiologically extreme version of this normal sleep, kind of similar to hibernation.
Now the obvious follow-up question:
Do butterflies dream?
I think not.