Just had the dreaded experience with one in Marriott London Plaza Parade Maida Vale. Very nice hotel and was not expecting it! The person I was sharing the room with was covered in red bites on his thigh after the first night. I found one in the sheets and was able to capture it under a glass for the manager after taking a picture first of course. They are not helping me at all though. Marriott's response is pitiful at best.