What are their bites like?; in the last couple of weeks I've had two instances of being bitten repeated times shortly after squirming in/out of a spider-infested entrance - first time something got down the back of my neck and bit my back 4+ times, and yesterday 4x on my head/neck (inside my helmet). I'm not sure what it was (couldn't see) but the bites are pretty vicious and take about 3 days to clear.