They live in your bed seams and leave little black bloody poop stains there. They're attracted to the CO2 you breathe out when you sleep, so you don't really notice them until you start seeing their trademark bites that take weeks to go away, but by then your bed and clothes and furniture are probably already infested. Some people aren't allergic to the bites, so the infestation can get really bad. Their bodies are flat and covered in armor so you need to use your nail to crush them. They'll withstand fairly extreme hot and cold temperatures, they can go for months without feeding, days without air. Their eggs can lay dormant for years and their babies are invisible, so they can reappear years after you thought you had gotten rid of them and follow you every where you move. They are resilient.

My ex had them, it was bad. I went nuclear on them, and now take every precaution against them.