I have alot of bug bites on my legs, but one has a bruise half around it. Should I be concerned and get it looked at?

Infected Insect Bite. Insect bites can cause redness, swelling and itching. In some people the amount of swelling can lead to bruising. However, if the area is more warm than the normal appearing skin, if it is very tender, and is spreading in size, see MD to rule out possible bacterial infection of the skin known as cellulitis which needs antibiotics promptly.