Satyrs and Sileni are 'spirits of wild life in woods and hills'... bestial in their desirs and behaviour, and having details of animal nature, either of a horse or of a goat. Classical authors constantly confused Satyrs and Sileni, but from the 4th century BC on Sileni are usually old and retain horse-ears, while Satyrs are usually young, and have taken over from Pan the traits of a goat. ... Hesiod makes them brothers of the Nymphs and calls them 'good-for-nothing and mischievous'... (Oxford Classical Dictionary)