I think it will depend on what country you are in. In the UK one has to see a GP to get a referral to a specialist unless one is going private (i.e. outside the NHS). In the US I guess you have to pay for every appointment or claim on insurance, so if you need to minimise costs I think it would make sense to go straight to a dermatologist, unless they cost more than GPs! A dermatologist should be familiar with all types of skin problems including bites, I would think.