Stormrage
Ever Present Taskmaster
I think the #1 should be your choice for sand, since #2 reminds me of dirt. Which is a different terrain type, as I`ve gathered from your post above.
Do you plan to use the Leaf and Flower both for the transport?
...also, do you plan to have "Paradrop" ability for any of the units?
Just some helpful information as I have pretty extensive knowledge of ants.
" The Horde" that people have referred to is better known as the army ants. You would probably want the eciton burchelli species. They are the "classic" army ant. Type in army ants on Google image and you'll see them. They had huge mandibles, which could leave significant cuts. The army ant units should be the highest powered unit both offensively and defensively. They are superior to every other type of insect. They are the real kings of the jungle. The Atta is a type of ant that cuts leaves, which they bring back to their colony, and grow fungus. When the ants are carrying back the leaves, they are completely defenseless from predators, unless they drop their precious booty. Therefore, you would probably want the worker to be represented by the leafcutting workers. Their large manbibles mean they you would want to give their major workers low offensive values, but high defense, since they were a relatively peacful species, unless a predator came into their territory. For a bombardment unit, you would have a acid spraying ant, much like the "gunner" from the Empire of the Ants game.
Just some suggestions. Hope they help.