Learning to identify bug bites or stings will help you get the proper treatment.
Bug Bites Pictures Slideshow: Identifying Bugs and Bug Bites - WebMD
Deer ticks can transmit Lyme disease to humans. Bad Bugs Slideshow: Identifying Bugs and Their Bites
Any time you're outdoors you risk conteact with insects and arachnids that can leave you covered in stings and bites.
This websites shows you how to identify different bug bites and the dangers of each one. This relates to the book in that the first night Brian is stranded in the woods he gets bitten by a large swarm of bugs and is all swelled up and dehydrated.