I don't think it was an Arachne and this is the only wiki to state it as such. I'm inclined to believe it was a rugaru. The picture is of an Arachne from the episode Unforgiven as a compare and contrast. Orion disagrees with me but I'm not just gonna write this off because of a different opinion. Truth is no one knows what monsters actually were because only vampires were specifically mentioned by name in that episode. It's mostly speculation on everyone's part but I'm inclined to use the 'If it walks like a duck' analogy here. I've posted screencaps of the monsters to let other users decided.
One monster we can conclude is a werewolf considering the pointed teeth and yellow eyes, they've always been portrayed as such.
Not sure what the next one is possibly another werewolf?This last monster has wormy skin which are associated with rugarus. Yes, arachnes have wormy skin as well BUT they also have two irises in each eye, all the monsters in these pictures have one. Lastly, this monster looks awfully similar to the Rugaru seen in the episode Family Feud. I've posted a screencap of that at the very bottom. As always decide what you will..not gonna argue about it but if it walks like a duck and talks like a duck then well..