|Calopteryx cornelia (Selys, 1853)
is endemic to Japan but is widely distributed and common within its range.
It can be found in Japan from Honshu to Kyushu, along fast-flowing mountain
forest streams from May to October. There are several similar species to
the jewelwing, and each manages to live along the same river by specializing
on a slightly different part of it. This species likes steeper, narrower
sections of river, deeper water and doesn't mind shade. Look for the males
perched on twigs overhanging the river and on rocks. Females will generally
be more aloof, surveying the scene from higher vantage points.
At 60-80 mm, this is one of the larger,
sturdier damselflies of Japan, and one of the most beautiful. The male
has a bright aquamarine metallic abdomen and thorax, with chocolate-bronze
wings. The female also sports a metallic body, with smoky wings.
Males perch over suitable egg-laying
sites, and advertise them to passing females through an elaborate display.
Males fly only with the forewings, beating faster than normal, and with
the hindwings held still below. The wings form a conspicuous X shape. The
male then throws himself onto the water above roots visible below. If the
female is interested, she'll perch and allow him to mate. Females lay their
eggs underwater. They grip onto the rootlets of trees and bushes, and drag
themselves under, spending between 20 and 120 minutes submerged. They achieve
this by absorbing oxygen from a thin layer of air trapped on the body and
the wings. Experiments have shown that females can survive for 120 minutes
without coming to the surface. Fortunately, this is more than enough for
them to lay their entire clutch of eggs, which take around 15 days to develop
and hatch into aquatic larvae. Both sexes benefit from the submerged arrangement.
The male, because no other male can disturb his female's egg-laying, can
be assured of fathering all the eggs she lays. The female, on the other
hand, doesn't have to put up with the unwanted attention of other eager
Coenagrion mercuriale is classified
as Least Concern on the IUCN Red List.