How do bed bug bites look like after you scratch?

See below: Most insect which draw a blood meal though a bite will cause a local reaction with redness, swelling, warmth and itch. It is often impossible to tell these apart, but bedbugs will often leave a straight line or repeat bites whereas other bugs like mosquitos, fleas, etc. May look scattered. After scratching, the area may scab over and ooze, especially if it becomes secondarily infected.