The beings that inhabit these suits clearly come from an environment utterly hostile to humans. The corrosive substance they use as a weapon may be the equivalent to water for them - but on this planet it's deadly. I've theorized as to how the substance could somehow be used to our advantage as part of an explosive weapons system.
As initially speculated by Shen, it does in fact appear this creature is restricted to the confines of its own hulking environmental suit. Unfortunately for our troops, the suit itself is a powerful physical threat regardless of the operator's status, as we learned with some astonishment in the field.
Although I was extremely hesitant to perform an autopsy on this creature before an extensive analysis of the fumes vented with regularity from its suit, my concerns were overruled by the rest of the senior staff due to our overbearing time constraints. It was with some relief that I discovered the most common element to be Argon, an otherwise harmless gas when handled properly. Although similar in size and physical structure to the Muton species, the "Andromedon" as it's come to be known does not appear to be of the same genetic design as the Muton. I stress design here because perhaps more so than all but the most extreme examples, the Andromedon was engineered to exist only within the confines of the environmental suit we see them wearing in the field. Destruction of this protective equipment results in a reaction similar to what we might see if a human astronaut were to remove their helmet in space - that is to say, a painful and unpleasant death within minutes. R. Tygan.