Hm, that sounds like it would do permanently visible damage.
Very good Biomass value, usefull to make areas uninhabitable but unsuitable for a 'delay enemies gathering to fight back by ambushing little groups of biomass without leaving survivors' phase.
Would you consider delaying it?
@Blackangel
Would something like 'spore, spawner, support' work?
Idea is "it grows spores (spore) that can be used as a poison by up to X tyranids hunting together with it (support). If a bundle of biomass gets poisoned with the spores but survives, the spores grow like cancer and consumed the biomass to spawn tyranids (spawner)'