Here is the rather famous account of Werewolves from Pliny the Elder’s Natural History 8.34) (for the full text: see Perseus). The Latin text on Perseus is incorrect, but fortunately Lacus Curtius is there to save the day.
Pliny, NH 8.34 80-83
“But in Italy they also believe that the gaze of a wolf is harmful—specifically that it will take the voice from any man they see first. Africa and Egypt have wolves that are slow and small, while the colder climates produce fierce and wild animals. We ought to believe with certainty that accounts of men turning into wolves and then back to themselves again are false; or we should be prepared to believe all the tales that are fantastic from as many generations.
Nevertheless, since the tale is popular enough that it has earned the curse-term “versepellis”, I will explain its origin. Euanthes, not unknown among Greek authors, reports that the Arcadians hold that a member of a family of a certain Anthus is selected by lot, transported to a certain lake in the region, and, after he hangs his clothes on an oak tree, he crosses the lake and enters the desert where he turns into a wolf and joins with others of his kind for nine years.
If he keeps himself from humans for this period of time, he returns to the same lake and once he has crossed it regains his form, except that nine years of age have accumulated. Fabius adds to this tale that he also regains his clothing. It is amazing how far Greek gullibility will go! There is no lie so shameful that it will lack partisans.
Similarly, the author Apollas who wrote the Olympionics, claims that Demaenetus of Parrhasia, when the Arcadians were still performing human sacrifices to Jupiter Lycaeus, sampled the entrails of a child who had been sacrificed, and transformed into a wolf. That same man transformed back 10 years later, became an athlete, and returned to the Olympic games as a victor.
It is also believed that there is a thin tip of hair on the tail of this animal which acts as an aphrodisiac—when the animal is caught, it has no force unless it is plucked while the animal is still alive.”
Sed in Italia quoque creditur luporum visus esse noxius vocemque homini, quem priores contemplentur, adimere ad praesens. inertes hos parvosque Africa et Aegyptus gignunt, asperos trucesque frigidior plaga. homines in lupos verti rursusque restitui sibi falsum esse confidenter existimare debemus aut credere omnia quae fabulosa tot saeculis conperimus. unde tamen ista vulgo infixa sit fama in tantum, ut in maledictis versipelles habeat, indicabitur.
Euanthes, inter auctores Graeciae non spretus, scribit Arcadas tradere ex gente Anthi cuiusdam sorte familiae lectum ad stagnum quoddam regionis eius duci vestituque in quercu suspenso tranare atque abire in deserta transfigurarique in lupum et cum ceteris eiusdem generis congregari per annos VIIII. quo in tempore si homine se abstinuerit, reverti ad idem stagnum et, cum tranaverit, effigiem recipere, ad pristinum habitum addito novem annorum senio. id quoque adicit, eandem recipere vestem.
mirum est quo procedat Graeca credulitas! nullum tam inpudens mendacium est, ut teste careat. item Apollas, qui Olympionicas scripsit, narrat Demaenetum Parrhasium in sacrificio, quod Arcades Iovi Lycaeo humana etiamtum hostia facebant, immolati pueri exta degustasse et in lupum se convertisse, eundem X anno restitutum athleticae se exercuisse in pugilatu victoremque Olympia reversum.
quin et caudae huius animalis creditur vulgo inesse amatorium virus exiguo in villo eumque, cum capiatur, abici nec idem pollere nisi viventi dereptum.