Does the flapping help?

Pack of Mutalisks
Flying swiftly on bat-wings
How's that work in space?

Starcraft, being science fiction, and a video game, has to take a few liberties with technical details. For example all the flying units kind of just float there by default, and move across the map at maybe 2x or 3x walking speed when you order them around. This is because the game would be less fun and balanced if your marines and tanks could be suddenly obliterated by enemy Banshees screaming by at Mach 6.

In game, we can try to explain it with some technobabble. Perhaps anti-gravity devices exist, but only work at slow speeds? Of course, this doesn't work for Mutalisks. They actually flap their wings to stay airborne and move around. The great blog Science of Starcraft tries to explain the wings as solar sails, but in the end the math doesn't work out. They conclude that the explanation for flying Mutalisks is: magic. I don't know about that... surely there must be a way they can fly, maybe it has to do with neutrinos?

They check in, but they don't check out

Nasty little roach
As loathsome as its namesake
And as hard to kill

My first thought when I saw this unit was called the "roach" was, that's a weird name for a Zerg unit! Most Zerg names are original names that have that alien feel. I mean we have Queen and Drone and Overlord, but at least those are reminiscent of the hive mentality. "Roach" sounds immersion-breaking.

But "Roach" is still an insectoid name, and it certainly does fit this Zerg unit! Roaches are scary, next to impossible to kill, and I don't know about you but I always hate seeing them. Unlike in the game, though, I do not recommend dealing with cockroaches with machine guns or flamethrowers.

They are coming

Incoming Zerglings!
A seething mass of creatures
Each with teeth and claws

The third race of Starcraft, and the most unique. Zerg play very differently from Terran and Protoss, and from just about any other RTS faction. It's interesting how unique they are: All Zerg units come from the same building, and they train in parallel, not in a queue. Their supply mechanic doubles as scouting, infrastructure, and transport. They can only build on creep, yet they want to take over most of a map. None of their buildings do anything, just unlock unit types. And their "ultimate" unit is a big ground guy who can't hit air or range.

And the humble Zergling embodies this race, just as the Marine and Zealot do theirs. Zerglings are cheap, but numerous. They are weak alone, but vicious in numbers. They are lightning-fast, and excel at hit-and-run and surrounding the enemy. They can take over the map early on, and enforce that control later.

The Zerg really are unique. Their influence is felt throughout gaming in the concept of the "zerg rush" or just "zerging." And we have the little Zergling to thank for that!