From the films, the Xenomorphs are always dripping some sort of fluid, and aside from making them creepy, and possibly solidifying into resin (from the way that it seems to stick to guns on the floor in a more congealed way than when it's dripping off their jaws), I was wondering if it served another purpose. If it solidifies into resin at some point, I was wondering if it would allow them to more easily cling to surfaces like ceilings, walls, etc. Then I saw this article on Engadget the other day that got me thinking (video in the link).
Climbing walls is one of those odd feats that scientific establishments seem compelled to master -- despite there being few practical applications beyond the ultimate in Marvel-themed Halloween attire. The latest to tackle the challenge are Paul Steen and Michael Vogel from Cornell University, who have stolen the sticky-feet technique of a Floridian beetle that apparently failed to file a patent. The technique relies on the surface tension of water and capillary action of fluids forced through thousands of microscopic holes. When moisture is pushed through the holes it creates a suction on a smooth surface, enough at this point for the team's prototype to hold a weight of 30 grams. When the water is retracted the suction disappears. If all goes well, future implementations of a similar size could hold 15 pounds, meaning with enough of them you could climb a wall -- without leaving a sticky mess behind.
I think that this is a rather interesting idea for how Aliens could wall crawl that would also explain the need for their bodies to use / exude a fluid. I'm not sure if it would function in space, but if there's some chemical reaction that allows them to speed the process at which the fluid turns into resin, they may be able to make it a stronger adhesive for higher gravity / zero gravity. Anyhows, just theory crafting, but I thought some of you might find it interesting.X