* Japanese name: Genjibotaru * Scientific name: Luciola cruciata * Description: Fireflies aren’t flies — they are beetles, as you can tell from the hard shell that protects their wings when they’re not flying. Adults are 12-18 mm long. They have black bodies and legs, and a red thorax. The most amazing thing about fireflies, though, is the bright green light they generate in their abdomens. Nothing else flying at night does this — if you see the green light, you know it’s a firefly.
* Where to find them: Near clean rivers, in the countryside. Adults fly from June to August, from Honshu to Kyushu. They can sometimes be seen in large numbers at night, looking like little green flying aliens. Their numbers are decreasing now in Japan as the amount of pollution in rivers increases. The larvae are nocturnal and live in rivers. They have soft, stretchy bodies but are strong enough to move stones around when looking for food.
* Food: Adults don’t really eat. Larvae feed on mud snails. They inject digestive juices into the snail and eat the body. After adults emerge from the larval stage they drink dewdrops from plant leaves, but don’t eat.
* Special features: Other insects may dance, chirp, emit pheromones or show bright colors to attract mates, but fireflies are one of the few insects that shine a light. The light-producing organ in the abdomen is made of a layer of a special chemical called luciferin on top of a reflector made of tiny crystals. By controlling the supply of oxygen to the luciferin, the insect can turn the light on and off, and so produce a flashing signal. Males flash their lights as they fly, and females respond by flashing their own lights. Females have wings but don’t fly — they signal to males that they see flying overhead. If you have a small flashlight, you can pretend to be a female firefly and signal and try to attract males.
The female lays her eggs four or five days after mating. The females often gather in groups, on damp moss near a river, and start to lay eggs around midnight, finishing at dawn. Even the eggs glow, because they too contain luciferin. The glow becomes brighter as the eggs develop, and the larvae glow too.