I have a problem with this. Other than the Queens, there is no evidence in the movies that the Aliens are anything more than particularly smart animals. Even the Queens are not portrayed as particularly intelligent. They use no tools, they don't appear to communicate in any way other than basic concepts common to most animals. They travel through space on a hijacked ship they didn't build.
Well, this puts me on ground I don't usually defend, but I would argue that historically whenever two ethnic groups are at odds to the point of genocide, they portray the other side as nothing more than particularly smart animals. I'm not sure that the claim of 'nothing but really smart' animals has much meaning, since the fully materialist view of humanity is 'nothing but really smart animals'.
I guess it is an open question, because the humans aren't able to communicate with the xenomorphs and so the movies at least leave it somewhat open, so you are free to see them as nothing more than really smart animals or as an intelligent race whose life cycle requires raping, killing, and consuming sentient beings to propogate. However, using evidence like 'they use no tools' and 'they don't appear to have a language' as proof of a lack of intelligence strikes me as little more than human-centric bias. These 'really smart animals' are capable of planning, coordination, and of understanding the purpose of and how to manipulate advanced technology. The show extensive ability to manipulate things mechanically, and do so with a purpose that implies they are able to imagine themselves as something other than themselves (for example shutting off power to blind their opponents is way above 'really smart animal' levels of planning and imagination in my opinion). And they show an ability to coordinate their actions that suggests that they are communicating in some fashion we don't readily observe (possibly tactile and olfactory, possibly 'ansible' or some sci-fi concept).
As far as I can tell, they are specialized adapted to feeding on sentients. Some one suggested that the fact one of them implanted in a dog suggested that they could use non-sentients to complete their life cycle, but I don't fully agree because the 'dog xenomorph' retained dog-like traits and did not appear to be a full 'adult' much less capable of transforming to a queen. There is the strong suggestion that they cannot achieve the full degree of maturity and sentience that they need to continue their civilization (nihilistic though it is) without implanting in sentients.
And yes, it is possible that only the Queens are true individuals as we'd understand the term. They are possibly superorganisms that count as a single sentient, although personally, I think that's a human-centric interpretation of the culture of social insects. Bees don't see their society as having a queen in a leader role. Bees are actually democratic and the most senior workers lead the hive. The queen mother is vitally important, but more in the same sense that a man sterotypically considers his sex organs vitally important, not in the sense of being a monarch.
