Stumbled across this:
http://www.youtube.com/watch?v=OzmZiZaj81o&feature=related
and this (check the last part of the page):
http://www.planetavp.com/al/Alien/DeletedScenes/index.htm
In a very disturbing scene it appears that the alien has the capability of taking a host body, live (Dallas) or dead (Brett) and somehow inject it with something to metamorphosize it into a new facehugger "egg". In the scene dead Brett is almost completely metamorphosized into an egg and Dallas is about halfway there (though still somewhat conscious and probably in a ton of pain).
Anyway, I was thinking about this and it makes a lot of sense to me. In the absence of a queen the alien would have to fall back on a secondary, less efficient, means of parasitic-like reproduction. By creating future face-hugger eggs (which probably have long term storage capacity) the alien sets the stage for a future infestation after its own relatively short lifespan comes to an end. I'm assuming that the alien has a relatively short lifespan due to it's worker/warrior insect-like characteristics relative to a "queen". It's also interesting that towards the end of the movie the alien seems much more sluggish when Ripley encounters it, suggesting that it might be approaching the end of its life cycle.
The idea of having an "intermediate host" isn't foreign in nature. Schistosomes are parasites that spend part of their life cycles in different hosts.
http://www.nature.com/nri/journal/v2/n7/box/nri843_BX1.html
So the idea of the aliens using a similar approach in the absence of a queen alien makes sense to me.
With a queen present, living hosts would be taken and cocooned for direct "impregnation" by one of her eggs. In the absence of a queen, hosts would be themselves turned into eggs to ensure that the infestation could continue at a future time when new hosts present themselves, such as when the crew of the Nostromo went searching into the crashed alien spaceship.
So this is my theory. Thoughts? Comments? Jokes?