Euphaea guerini - at last

On 13 April we were birding in Xuan Son, but I also searched for dragonflies. Euphaea masoni was now very common and everywhere on the larger streams, flitting back and forth in constant arial battle, or resting on the stones. But on the small and shaded streams in the forest I also ran into them, and for some reason the ones on the larger streams seemed all dark when flying, but the ones on the small streams showed bright green flashes of their hind wings. Could it be that these were in fact E. guerini, for which I had looked in vain last year? Maybe it was a spring species? Anyway, the easiest way to separate the two species is by taking a look at the base of S9, where E. guerini has a tuft of hair. And indeed, in hand it showed this characteristic nicely. Also the differences in wing darkening (apart from the green flashes, which are more reddish in E. masoni and mind you, the closed wing of both species displays a dark blue shine) were evident, with much darker bases to the front wings and no light tips to the hind wings for E. guerini, although the latter character is somewhat variable in E. masoni and cannot in itself serve to identify. The specimens seemed to also average smaller, evident in the two in below scan, but there appeared to be some variability there too. Nevertheless, a nice addition to the list!

Picture taken in a dark place with flash, Euphaea guerini, male. The green you see is the shine of the topside op the left hind wing. 

The tuft of hair on S9. What will be its purpose, besides to aid identification?

Scan of the two species, E. guerini on top and E. masoni below. E. guerini curled up during preservation. The difference in darkening of the front wing is visible. E. masoni is 52mm in total length, HW 32mm. HW of E. guerini here is 28mm.