A skin rash from an insect bite is an allergic reaction that affects the skin, according to MayoClinic.com. It is not uncommon for an insect bite to cause hives, but the severity of the rash can vary from person to person.

Bug bites are an annoying and common occurrence, especially during the warm spring and summer seasons. Common culprits include mosquitoes and flies. Unlike stings, most bug bites do not involve injection of venom into the skin. Instead it's saliva from the bug's mouth that causes local irritation and swelling.

Recluse spiders--also known as violin spiders or fiddleback spiders, owing to the distinctive violin-shaped marking on their backs just behind the eyes--are one of the few species of spiders known to cause medically significant bites.