LAST EDITED ON 03-29-16 AT 12:37 PM (EST)

Staph infections can also be acquired by bathing in contaminated water. If the Brain tribe camp was located nearby where a fresh water stream empties into the salt water of the ocean, that water could/would carry the bacteria responsible for the infections. Usually originating in upstream animal fecal matter.

At some point the salt water will neutralize and dilute those organisms, but if our heroes swim, soak, and wash themselves too near those mini-estuaries, they could very well pick up those infections where they have insect bites. And, as you pointed out, those insects might also be the vectors for the bacteria.

Remembering that picture of Darnell. If they are pooping in the ocean and swimming in that, well, that's another possible source of infectious bacteria.

As to spider bites, I was bit while I slept one night. I strongly suspect that it was a spider, and he bit me four times traveling in an arc on my side. About a half inch dia. circle of flesh rotted at each location, and it was over a half a year before it healed. Still have scars. I hate spiders. I'll leave the garden ones alone, but inside spiders will die.