I personally no longer watch those channels anymore they're pretty much full of crap. In fact I did away with sattelite service at my house and even if they have those shows on hulu there is much better stuff to watch. Which brings me to the subject of killer aliens. You should check out that show V. It is about killer aliens and secretly they are reptiles that disguise themselves as humans. That's cool. It also stars Laura Vandervoort as one of the aliens. She's pretty hot, It also star Morena Beccarin as one of the aliens she's not too bad looking either although I liked her a lot better in "Firefly" where she had longer hair.
I find both "V" and "Firefly to be much more informative and educational than anything on the discovery channel or it's animal whacko sister channel. Which is sad considering both shows are science fiction and the discovery channel is supposed to be an educational channel.