Spiders that are moth larva predators?

Question

At this time of year we note certain larvae forming a cocoon (I hope I am using the correct term) against window frames, sills, grill covers, etc. Recently I have noted a speckled brown and grey spider about 2 cm from leg to leg with its fangs imbedded in the cocoon. Anyone here with an opinion on what the predator and prey are?

Answer 1

It sounds like a wolf spider. They would be the type, along with jumping spiders that wander about and hunt their prey.
http://images.google.com/images?q=wolf+spider&hl=en&safe=off&pwst=1&um=1&ie=UTF-8&sa=X&oi=images&ct=title