Ctenus medius Keyserling, 1891 is a common species in several spots of Mata Atlântica, however there is a great lack of studies in all aspects of its natural history. This work aims to elucidate aspects of ecotope preference compared to large spiders, and to provide data on the development of chromatic patterns during its life cycle. The observations on the behavior of C. medius were done in the campus of Centro Universitário de Barra Mansa (UBM) by means of observations and nocturnal collections using cap lamps. For observations on the development of chromatic patterns, spiderlings raised in laboratory, hatched from an oviposition of a female from campus of UBM, and others spiderlings collected in field were used. The field observations indicate that: C. medius seems to prefer ecotopes characterized by dense shrub vegetation or herbal undergrowth; Lycosa erythrognatha and L. nordeskioldii seems to prefer open sites; Phoneutria nigriventer seems to prefer shrub vegetation and anthropogenic ecotopes as rubbish hills; Ancylometes sp. seems to prefer ecotopes near streams. Concerning chromatic patterns, it was observed that males and females show well distinct patterns during the last two instars, allowing distinction by sex without the use of a microscope. Through chromatic patterns it was also possible to draw a distinction between C. medius and C. ornatus longer that 3 mm cephalothorax width. 69 specimens of C. medius (males and females) collected in the campus of UBM did not show a striking polymorphism in chromatic pattern, but one among 7 adult females collected in National Park of Itatiaia, showed a distinct chromatic pattern.
Ctenus medius; Ctenidae; natural history
