They can see us but we cant see them, they can take different forms like animals and humans but they themselves are made of fire. Their life expectancy can go in thousands of years and they can travel from earth to outer space in seconds without need of any vehicle. The cosmic rays and other dangerous radiations of outer space don't stop them, they even don't require air unlike us. There are large number of instances when they have taken over human bodies. They are more prominent in lonely-deserted places. Many people have seen them and many have felt their presence, one day you might also meet them.