When bruising occurs four to eight hours after a bug bite, consider the possibility of a spider bite, such as that of a brown recluse, which is known to leave a distinct bruise, according to Everyday Health. Seek medical attention immediately if a brown recluse spider bite is a possibility for the bruising or if any symptoms of anaphylaxis, such as shortness of breath or swelling of the mouth, occur.
About.com advises treating all common bug bites by applying ice to the affected area, alternating it on and off the site of the bite or sting in 20-minute intervals. When pain is present, take a pain reliever to alleviate it.
MedicineNet recommends keeping the area clean by washing it with soap and water. Apply a baking soda and water paste, calamine lotion or another anti-itch cream to the area to prevent pain and itching. When necessary, use an oral dose of antihistamine to alleviate itching.
The best way to prevent bug bites is to prevent them, says MedicineNet. Avoid areas that are likely to harbor spiders and bugs, such as piles of brush, woodpiles, tall grass and dark, damp areas. Wear long sleeves and long pants when in such areas, and apply insect repellent.