^Simple projectile weapons that cause the creature to release a cloud of molecular acid. If this is done in a pressurised environment like a spaceship then, well, goodbye atmosphere. Oh and I'd say a gestation cycle from spore to larva to adult in under 24 hours is astonishingly virulent. As for the life-cycle, it's clearly efficient as with every victim it takes it adds to it's own numbers; either as a host or in the absence of a queen, in the fabrication of a new spore. Indeed, the idea of self replicating nano-machines as a weapon of mass destruction is a well know sci-fi trope, this is basically the same concept but on the macroscopic scale.
Regardless, the efficiency of a weapon is dependent on the nature of the enemy for which it was intended. We have no idea of this race's motivations. It could the purely a weapon of terror meant to impede and weaken an enemy, not achieve total victory on it's own. But like I said, this could just be the very least of their arsenal...or a gardening tool.