There were domesticable animals on Vland — most notably, the Poni (found on IISS livery) — as well as genuine cities, and (after rigorous processing) edible plants.
One is reasonably surprised on why the only major Contact plague was the Plague of Duskier.
If you like your Vilani genocidally aggressive, a great way to neuter their war machine is by inflicting upon the Ziru Sirka wave after wave (after wave, after wave) of disease. And if they get eliminationist, the Terrans have a huge lead on genetical building entirely new horrors, while the Vilani desperately try to get a decent germ theory up and running…
“Not a very nice style of warfare. But really effective.”