This evening, just before dusk, I noticed a White Butterfly flying low around a small area of Clivia that we have growing at the side of our house. It's flying pattern was small and it was keeping quite close to the leaves. I watched it fly back and forth, back and forth and, after about 15 minutes of this, it settled under a Clivia leaf and just stayed there. An hour later I looked back there and saw that another White Butterfly had joined it. Although not hanging upside down under a leaf, the second butterfly was quite settled on an adjoining leaf.
Given my enormous interest in butterflies, I'm surprised to realise that I've not really given much thought to where they might go at night.
I've asked about and found this information..............
Butterflies 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.
REF: Rainforest Expeditions - Do Butterflies Sleep?
The word “roost” probably brings to mind chickens perched on their nests, snuggling down for the night. But chickens aren’t the only things with wings who make roosting a part of their regular activity – butterflies do it too! Sometimes species roost on their own, while others prefer large groups, but all butterflies need safe places to take shelter from time to time, and your butterfly garden can help provide those spaces.
Roosting is the word used to describe butterflies at rest for more than a few minutes at a time. All butterfly species roost overnight, and during wet or chilly weather. Some species even roost all winter long, such as the migratory monarch population that overwinters in Mexico. During the roosting period, butterflies sometimes enter a state known as “torpor“, in which they drop their body temperature, heartbeat, and respiration as low as possible to conserve energy.
Most butterflies roost upside-down under the shelter of leaves, but others choose cracks in rocks or the trunks of trees. Because butterflies are most vulnerable when they’re at rest and unaware of their surroundings, it’s vital that they blend in to avoid the notice of predators. Most butterflies have duller patterns on the undersides of their wings that will help them camouflage or fade into the background as they roost.
In your own butterfly garden, you can help roosting butterflies by providing places for them to take shelter. Some companies offer so-called “butterfly houses” for this purpose, but in my own experience, butterflies rarely use these and they generally just wind up providing a place for wasps to build nests. Instead, be sure to make shrubs, tall grasses, and even trees a part of your butterfly garden. Snags of dead branches or rock piles can also provide shelter. Most importantly, if you come across roosting butterflies, resist the urge to touch them, even just “to see if they’re still alive”. They will move when they’re good and ready.
REF: Birds and Blooms - Roosting Butterflies
This morning (the morning after) I checked at 7.30am, just as the sun was rising, and noticed that the butterfly under the leaf was still there whilst the other had gone.
The butterfly under the leaf was just beginning to feel the suns rays on it's wings. When I checked back 30 minutes later the suns rays were fully shining on its wings.
Knowing the cleverness of butterflies, coupled with my observation as to the length of time the butterfly took, flying around and around the patch of Clivia checking out leaves, there is no doubt in my mind that the clever thing deliberately chose the location because it provided (1) protection from above (by way of the wide, flat, Clivia leaf) and (2) was directly in the path of the rising sun's rays that would warm its wings and enable the butterfly to fly.