An early indication of pupating is when the Blue-streaked Nettle Grub (Parasa lepida) moves around aimlessly LINK. Subsequently its dorsal blue stripe turns dark, followed by the rest of the body (above: pupating grub on right). It stops eating and may either discharge a black liquid that stains the leaf surface (below). Others may discharge a larger than normal black pellet. Should this pellet lands in water it may partially dissolve giving a localised black stain.
It returns to the branch or the underside of a leaf to spin a cocoon before pupating (below).
This was usually seen in the late evening, continuing through the night to complete the cocoon by the early hours of the next morning (below).
Only then will it form the thick oval pupal covering that is about 12-15×7-10 mm (below).
The entire process of cocoon formation can be seen in the video below.
In nature the cocoon is reported to be found buried in the soil or among leaf litter. However, I did come across one cocoon attached to the underside of a leaf in the garden. In my observations, the cocoons were attached to the underside of a leaf except one attached to the twig. This can be because the grubs were confined to the leafy twigs by a water barrier.
31st October 2016