I found this Asian Slim Damselfly (Aciagrion occidentale) sitting on a blade of grass in my garden. I was using my Canon EOS 5D Mark III with Canon EF 100mm f/2.8L Macro IS USM lens illuminated by Canon MT-24EX macro twin light flash. This looks like a male Aciagrion occidentale. Despite being quite a common damselfly of South India and SriLanka, I could hardly get any Literature on this damselfly. It was explained by Laidlaw, F. F. 1919 in his monumental work A list of the dragonflies recorded from the Indian Empire with special reference to the collection of the Indian Museum explained this Damselfy for the first time. Even though it is recorded in checklists and other feild guides on dragonflies of South India and Sri Lanka, I failed to get any concrete description, ecology or breeding habits of this elusive yet common damselfly. Aciagrion is a genus of damselfly in family Coenagrionidae. They are commonly known as Slims. Asian Slim Damselfly (Aciagrion occidentale) is found in Southern India, Sri Lanka and questionably in south Asian counties where another damselfly Aciagrion borneense resembles this very very closely.
Male Aciagrion occidentalehas a long and slim abdomen. Sides of 1 to 3 pale sky blue; of 4 to 7 pale yellow, of 8 to 10 blue; all except 9 marked in black dorsally: 1 with a broad band, on 2 the band joins a narrow apical ring, 3 to 7 bronzed black dorsally with pale blue spots dorso-laterally, on 7 the black is broader apically, on 8 a narrow triangle; on 10 a small X-shaped dorsal spot, 9 fully blue. Head mainly black, genae, anteclypeus, frons and labrum pale sky blue, the last with a median black spot; postocular spots blue. Eyes capped black, then bottle green changing through pale greenish yellow to very pale blue below. Prothorax: anterior lobe blue, posterior lobe black, sides blue edged yellow. Thorax bluish black dorsally up to between humeral and first lateral sutures; sides pale sky blue; antehumeral stripe narrow, greenish yellow. Legs pale blue with black on extensor surfaces. Wings hyaline, pterostigma greyish black, that of fore wing nearly double that in hind. Anal appendages black, inferiors less than half the length of superiors. Abdomen 23-24mm; hind wing 15-16mm.
Female similar to the male, but ground colour of face, occipital stripe and antehumeral stripe is pale yellow; eyes with a black cap ringed in pale brown, then olivaceous fading to yellow below, 8 with a band of black, 9 with a dorsal spot from base to a third of segment, 10 fully blue or with a small subdorsal apical blue spot. Anal appendages black, very small; vulvar scale pale blue. Abdomen 15—16mm; hind wing 16mm.
Aciagrion occidentale is widely distributed in grasslands in open grass besides weedy ponds and marshy areas. The larva has not been described. Despite being a very common damselfly as noted by The IUCN Red List of Threatened Species I could hardly find photos of this Damselfly on the social media or on the nature websites.