蜉蝣(you)目通稱蜉蝣(you),具有(you)古老而特殊(shu)的性狀,是最(zui)原始的有(you)翅昆蟲。體(ti)形較小(xiao)或中等,細長,體(ti)壁柔(rou)軟。頭部(bu)(bu)小(xiao),觸角短,剛(gang)毛(mao)狀。復眼(yan)(yan)(yan)發達,雌性的復眼(yan)(yan)(yan)常左(zuo)右遠離;雄性的復眼(yan)(yan)(yan)常較大,左(zuo)右接近,且每(mei)一(yi)復眼(yan)(yan)(yan)上(shang)下(xia)部(bu)(bu)小(xiao)眼(yan)(yan)(yan)面往往不同,一(yi)般上(shang)半部(bu)(bu)小(xiao)眼(yan)(yan)(yan)面大于下(xia)半部(bu)(bu),也(ye)有(you)二部(bu)(bu)分(fen)完(wan)全分(fen)隔者。
這種(zhong)在個(ge)體(ti)發(fa)育中出現成(cheng)蟲(chong)體(ti)態后繼續蛻皮的現象在有(you)翅(chi)昆蟲(chong)中為蜉蝣目所僅有(you)。這種(zhong)變態類型特(te)稱為原變態。成(cheng)蟲(chong)不進食,壽命短(duan),一般(ban)只活幾(ji)小時至(zhi)數天,所以有(you)“朝生(sheng)暮死”的說法。蜉蝣成(cheng)蟲(chong)在其短(duan)暫(zan)一生(sheng)中負責交配,繁衍后代的任務。