Emma field cricket

This insect belongs to the order Orthoptera of the family Gryllidae. It is the most common species of cricket living in Japan. It was named after the face, which resembles the face of King Enma. It is found throughout Japan. It is 26 to 32 millimeters long and has a shiny black-brown body color. Its head is round, with a brown eyebrow-like pattern above the compound eyes, and the area around the mouthparts is also mostly brown. The dorsal part of the male's forewings is the sound organ, which produces sound by rubbing the left and right forewings together. Its hind legs are sturdy jumping legs, and both males and females have long horns extending from the tip of their tails. The female's ovipositor is spear-shaped and about 20 millimeters long.

They emerge once a year, with adults appearing from summer to autumn, and are often found on riverbanks, grasslands, and farmland, where they make shallow depressions in the ground near the roots of grass and hide there. They are omnivorous and eat vegetables, so they are often pests in farmland. They grow in a short day, growing faster when the days are short, overwintering as eggs, and emerge from late summer to autumn after molting 8 to 10 times. Males are known to make about four different calls. The "korokorokoroririri" tone is a territorial claim, and when it changes to "korokorokorori" it is a call to females. The tone changes to a different sound when mating or when males are fighting.

The Taiwan emma cricket T. taiwanemma is found in warm areas south of Honshu, while the Yezo emma cricket T. yezoemma is found in Hokkaido and northern Honshu. Both species are about the same body length and look very similar to the emma cricket, but the Taiwan emma cricket often has a brownish body and its ovipositor is short compared to its body length (the emma cricket's is long), and it hatches twice a year and overwinters as larvae. The ovipositor of the Yezo emma cricket is slightly longer than that of the emma cricket, and it overwinters as eggs, and it often coexists with the emma cricket.

[Yamazaki Egane]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

昆虫綱直翅(ちょくし)目コオロギ科に属する昆虫。日本にすむコオロギ類中でもっとも普通種。顔面の感じが閻魔(えんま)大王の顔を連想させるところから名がつけられた。日本各地に分布する。体長26～32ミリメートルで、体色は黒褐色でつやがある。頭部は丸く、複眼の上部に茶褐色の眉(び)状紋があり、口器付近もほぼ茶褐色を帯びる。雄の前ばねの背面部にあたる部分が発音器で、左右の前ばねを擦り合わせて音を出す。後肢(こうし)は頑丈な跳躍肢となり、雌雄とも尾端から長めの尾角を出す。雌の産卵管は槍(やり)状で、長さ20ミリメートル内外である。

　1年に1回発生し、成虫は夏から秋にかけて出現し、河原、草原、畑地に多く、草の根際に近い地面に浅いくぼみをつくってそこに潜む。雑食性で野菜も食べるので、しばしば畑地の害虫となる。成長は、昼が短いと成長が早くなる短日型で、卵越冬(らんえっとう)し、8～10回の脱皮後、晩夏から秋にかけて羽化する。雄の発音には四つほどの鳴き分けが知られている。「コロコロコロリリリ」という調子は縄張り（テリトリー）の主張で、これが「コロコロコロリー」と変わると雌を呼ぶ声である。交尾をしている際や、雄どうしのけんかの際には別の声に変わる。

　本州以南の暖地には、タイワンエンマコオロギT. taiwanemma、北海道と本州北部にはエゾエンマコオロギT. yezoemmaが分布する。両種とも体長がほぼ同じぐらいでエンマコオロギによく似ているが、タイワンエンマコオロギは体が茶褐色がかるものが多く、産卵管は体長に比較して短く（エンマコオロギは長い）、1年に2回発生して幼虫越冬する。エゾエンマコオロギは産卵管がエンマコオロギよりやや長く、卵越冬し、エンマコオロギとはしばしば混生する。

［山崎柄根］

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