Trace fossils from nymphs of mayflies (Ephemeroptera : Polymitarcidae = Ephoronidae) are described as Asthenopodichnium xylobiontum n. g. n. sp. from the Late Miocene (Pannonian) of the Vienna Basin (e. g. Hennersdorf, Brunn- Yösendorf). The trace fossils are burrows in drifting woods from a limnic environment. Similar burrows are known in fossil woods from the Late Tertiary brown-coal in Germany (Lower Rhine- District) and recent in woods in lakes and rivers from the Paleotropis, Neotropis and the Southeastern USA (e. g. Tortopus, Asthenopia, Povilla). It is the first occurrence from Polymitarcids in the Miocene of the Vienna Basin and it suggests a warm-temperate climate in the Pannonian (Zone E) in this latitudes.