The life cycles of the burrowing mayflies,Ephemera strigataEaton andE. japonicaMcLach‐lan were studied comparatively between upper part and lower part of a small tributary of the Yoshino River.E. strigatawas more common thanE. japonicain the studies areas.E. japonicawas found only in the upper part and in tiny tributaries of the stream.E. strigatawas univoltine in the lower and in the upper parts of the stream. However, the population falls into two groups, one of which emerges in early May and the other in summer. Water temperature seems to be one of the factors affecting the variable life cycle ofE. strigata. E. japonicais univoltine. Emergence of this species was observed from June to August.