Otoha had been complaining about spiders, and Thanatos had seen some evidence of their webs. However, he hasn't seen any further sign of them. He's actually more worried about the spirit cats Tidus and Buttercup mentioned. Something that could drain energy at such a distance would be disastrous in an enclosed space like this.

"I'm not sure. There are others that seem easier, but they don't then lead anywhere. There's something like a tunnel up here and a flat enough landing for everyone to take a break."