Like many species in its genus, A. cylindrogaster has an extremely elongated abdomen, resembling a twig or pine needle. Female body length is about 30 mm. Color ranges from green to brown. Males are slightly smaller (around 25 mm), but otherwise look similar. The abdomen can be bent upwards.
Ariamnes cylindrogaster hunts other spiders, using a simplistic web, which it constructs between trees. In Japan, almost 96% of its prey were found to be spiders in 24 species from 11 families.
