Peninsular Malaysia has three Vestalis species - Vestalis amethystina, Vestalis amoena and Vestalis gracilis. Vestalis gracilis is easily told apart from the previous two species based on the thoracic marking. However, both Vestalis amethystina and Vestalis amoena are similar to each other in overall marking. The only character used to distinguish both the species is their anal appendages.
Vestalis amethystina - male
Hutan Simpan Gunung Tebu, Terengganu
Vestalis amoena - male
Taman Negeri Rompin, Pahang
The anal appendages of Vestalis amethystina and Vestalis amoena are different (see images below). Close inspection on the anal appendages is needed for proper species identification.
anal appendages of Vestalis amethystina. top = lateral view, middle = dorsal view, and bottom = ventral view
anal appendages of Vestalis amoena. top = lateral view, middle = dorsal view, and bottom = ventral view