Peter is completely calm, almost nonchalant. At least on the surface, because he's inwardly facepalming at the two continuing their fight when they are right outside an acromantula nest. It's like they want to get themselves in even more mortal danger.

So all he says, quietly, is, "I wasn't kidding about the acromantulas. Maybe fighting for your lives against something else will help you gain some respect for each other."

The spiders are smart and devious but he can already tell they're gathering, even if he can only hear a few stray clicks and rustles. So he casts a charm. It's mostly smoke and distraction, but the herb he tosses into it does have the effect of warding off the spiders a few seconds longer. The second charm, under the cover of the smoke is a dissillusionment charm. Cheap, and they could still find him by touch or by accident, but it should achieve the effect he's looking for. Namely, the appearance of being gone entirely from the scene.