* Japanese name: Ryukyu hagurotonbo
* Scientific name: Matrona basilaris japonica
* Description: The Ryukyu damselfly is a sturdy, brightly colored insect. At 51-65 mm long, it is large for a damselfly. Males have brilliant electric-blue bodies and two pairs of dark-blue wings, although there is a sky-blue pigment nearer the wing base. Females are drab compared to males, having transparent, slightly brown wings. Their bodies are green.
* Where to find them: In Okinawa and Amami Oshima, flying over and perching on the banks of clean mountain streams and rivers. Females visit streams to lay their eggs in plants growing in the water. They have a sharp, knifelike ovipositor (egg-layer) that they use to cut a hole into plant stems before inserting an egg.
* Food: Other flying insects, such as mayflies. Damselflies are carnivores and possess strong biting and chewing mouthparts. Larvae spend one to two years underwater, depending on the amount of food they can catch — if they eat lots of food, they can develop faster. Then they climb out of the water and transform into winged adults, living for four to six weeks, again depending on the food supply.
* Special features: The group of damselflies to which the Ryukyu damselfly belongs (the Calopterygidae) are unusual in that they have highly developed fighting and courtship displays. Males fly at each other, beating their forewings but holding their hindwings open, in ritualized, looping flight patterns. While the ritual minimizes the risk of physical damage, the damselfly uses up lots of energy to fly like that, and only males in good condition can keep it up for long. During courtship, males float on the surface of the streams, holding their hindwings out for the females to examine. If the female likes what she sees, they copulate. When they mate, males have another trick, not up their sleeves but on the second segment of their abdomens, next to the thorax. This is the location of the penis, and in damselflies and dragonflies it is more like a Swiss Army knife than a penis. The Ryukyu damselfly’s penis has horns on the head like those of a ram, and it uses the horns (covered in backward-pointing barbs) like a pipe cleaner, to clean out the female’s genitalia of all the sperm that might be stored inside from other males. In this way he ensures that when the female lays her eggs next, she uses his sperm and not that of a rival.

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