Whats this bullsh*t Web traps appearing in spider areas?

In some areas with many spiders like cloakwood there's points if you walk over them a spiderweb gets shot at your party. Imoen can't find any traps there and anyone in the area is completely helpless if attacked. So all I can do is trying to lure out the enemies and than activate it and wait for an hour (okay its not THAT long) for it to end.