Different kinds of insect bites will cause people to have different reactions. For example, mosquitoes cause a small, itchy lump on the skin where they bite, but it is generally harmless. Fire ant bites usually cause a stinging rash and in extreme cases, a hard lump will form on the skin with a boil on top. Bedbugs give you rashes all over your skin, and in extreme cases, itchy blisters will form. If bitten by a poisonous spider, you will need to visit the ER for treatment. A spider bite that requires emergency treatment will look like a burn, with the affected skin appearing to be punctured and the area feeling painful and itchy. A bee sting, on the other hand, is identified by a white spot that appears around the red pinpoint-looking mark on the skin where the stinger pierced the skin. Most harmless insect bites look like small, soft lumps and can be treated at home with an ice pack on the area as a first-aid measure.