Welcome to Gaia! ::

Kill team, oh yes. This does call for the Imperial Guard with its rugged individuals.

Can't Tyranid's exchange bio matter or something? When you upgrade a Tyranid maybe it gets morphed or added onto?

I thought of something similar, but I also thought it was a bit far-fetched and I would get berated by Tyranid fans. I see now that it is not as far-fetched as I thought, unless you don't know what you're talking about.

Actually something like that makes sense. They absorb all bio-matter and new genus strands and the next battle you get new beasts. Just look at the Scythed Heirodule and the Barbed Heirodule.

The problem arises when the RPG element in Dawn of War 2 comes into play - specifically how you can remove and store wargear. Once you evolve a trait, it's sort of difficult to suddenly lose it without risk of biological defects, serious injury or death.

Nids can adapt to the situation, so the chance of genetic defects is limited at best. Remember that we are talking about a massive bio organism here that sends millions of pods into the first wave just to check on the planet's atmosphere and other peripherals. From that first wave the Hive Mind gathers all the info it needs and both adapts its organisms and the planet itself.

Source: Warriors of Ultramar.

Individually smaller Nids are weak. Read a book and you'll see this. Guardsmen can easily kill lesser Gaunt species with good firing discipline. Smaller Nids are employed to swamp the enemy as probes for heavier assaults, ammo-wasters and diversions. (see: Apocalypse doubters)

Personally I could imagine large broods (30+) of Nids attacking small squads of elite veterans that you've built over the course of the game. Come on, just imagine the coolness of such a scene: A dozen space marines facing off against seemingly endless tides of critters just like in the codex books, mowing down everything in range while the survivors are hacked apart by commanders and assault specialists.