Doleschallia bisaltide, the autumn leaf, is a nymphalid butterfly found in South Asia, Southeast Asia, and Australasia. In Australia it is also known as the leafwing. Wikipedia
Please check this video from Pupa to Butterfly
Special thanks to Mr Foo Jit Leang for the guidance.
When a butterfly comes out of the chrysalis, it has an abdomen full of liquid. It has been pumping that liquid around to put pressure on the chrysalis from inside to make it split. When it crawls out of the chrysalis, it has tiny little wings with channels for the liquid (which is not blood; it’s more like hydraulic fluid). The butterfly hangs on something so the wings have room to expand
Then it pumps the fluid into the channels in the wings (not veins). The hydraulic pressure expands the wings to full size. Some chemical things happen, and the wings go from floppy to stiff. I’m not sure of the details, but this ends up with solid channels where the fluid was. To maintain the pressure in the little channels during this process, there had to be a sufficient volume of fluid in the pumping chamber in the abdomen. Once the wings harden, this fluid is no longer needed. It is expelled in a gush of liquid that is referred to as meconium. (Yes, it’s the same word that we use for a mammal’s first bowel movement, but it is substantially different.)
The liquid that comes out of the butterfly after its wings are fully expanded is a normal and necessary byproduct of the hydraulic engineering that expands the wings. It is expelled because it has done its job and is no longer needed. (Mary Arneson)
