What is the difference between mosquito bites and bed bug bites?

Mosquito bites often cause a raised, itchy bump soon after a bite, while bed bug bites may appear later and can occur in lines or clusters. Both can look similar, and bed bug marks can also be scattered. Timing and bite patterns are clues, but they cannot reliably identify which insect bit you. (CDC: Mosquito bites; CDC: Bed bugs)

Look for pest evidence as well as skin marks. Bed bugs may leave live insects, shed skins or dark spots around mattress seams and bed frames. If the cause remains unclear or the skin reaction is worrying, seek medical advice rather than assuming every new mark is a bed bug bite. (EPA: How to find bed bugs; CDC: Bed bugs)