No, it isn't an alien, I'm alerting you to. It is common dryer lint, but wait... that lint could literally blow up in your face. Homes and apartments have burned to the ground after a gas dryer explosion and it is so needless.
I recently had my gas dryer vent pipe cleaned by a man who does chimney cleaning too. He showed me a plastic grocery bag full of lint that he sucked out from the pipe on the roof. It is a miracle that it didn't explode! He also warned me that the CO2 build-up in the laundry room was a danger to the entire house.
We are in a one-story house with the laundry off the kitchen leading to the garage. In addition to that, guess where I kept my fire extinguisher? You guessed it, above the dryer! My vents had not been cleaned for 5-6 years and the drying time had gone from 1 hour to 3-4 hours per load. I was about to buy a new dryer... which would not have helped without cleaning the vents.
I was just lucky! Don't wait to find out what your luck is.