A few dragonfly species in Peninsular Malaysia are in red colour - Aethriamanta brevippenis, Crocothemis servilia, Lyriothemis biappendiculata, Orchithemis pulcherrima, Orthetrum chrysis, Orthetrum testaceum, Rhodothemis rufa, Tramea transmarina and Urothemis signata. Many laymen and beginners find it difficult to tell them apart. Quite frequently I receive requests from enthusiasts asking me to help on id for photos taken by them. Well, here are a few tips that may help to identify these red dragonfly species.
I would rather to divide them into large and medium sized red dragonflies. Crocothemis servilia, Orthetrum chrysis, Orthetrum testaceum, Rhodothemis rufa, Tramea transmarina and Urothemis signata are large sized red dragonflies whereas Aethriamanta brevippenis, Lyriothemis biappendiculata and Orchithemis pulcherrima are medium sized red dragonflies.
To identify large sized red dragonflies, you may first focus on the colour of eyes - red eyes or brown/dark eyes. If brown/dark eyes, there are three possibilities - Orthetrum chrysis, Orthetrum testaceum and Tramea transmarina. These three brown/dark eyes red dragonflies could be differentiated further by observing their body (thorax) colour and marking on the tail (the tip of abdomen). If the thorax is light colour and tail is red, then it is Orthetrum testaceum; if the thorax is dark and tail is red, then it is Orthetrum chrysis; if the thorax is dark and tail is dark, then it is Tramea transmarina.
On the other hand, if you notice the eyes are red in colour, then there are three possibilities - Crocothemis servilia, Rhodothemis rufa and Urothemis signata. These red eyes dragonflies could be differentiated further by marking on the back of its abdomen and dark patch at the wing base. Crocothemis servilia has a thin black line/strip on back of its abdomen; Rhodothemis rufa lacks of this black line/strip; Urothemis signata has two dark spots at the end of its abdomen (dorsal view) or it can be identified by having obvious dark patch on its wing base.
For medium sized red dragonflies, one needs to pay attention on the body (thorax) colour and dark patch on wing base. Orchithemis pulcherrima has yellow/brown thorax, and dark thorax are observed for Aethriamanta brevippenis and Lyriothemis biappendiculata. These two dark thorax species could be further differentiated by paying attention to their wing base. Aethriamanta brevippenis has dark patch on its wing base, and this character is absent for Lyriothemis biappendiculata.
Now you may dig out your photos to do the identification yourselves. :)