Individually, this particular species poses no significant threat. However, an insatiable appetite coupled with a tendency to blindly feed on anything that moves, makes this a very dangerous creature when encountered in large numbers (early on in the game a large group of them kill an Australis).
Rigel is a metamorphical being, meaning it can change its looks when getting older. Its adult form is Cebalrai. It is named after the star Beta Orionis, the traditional name of which being Rigel.