Second are the toxins. The naturally occurring poisons that microorganisms produce. You should recall ergotism in a previous unit. The targets of biological agents include soldiers, civilians, crops, and livestock.
Biological weapons are lethal, ideal for surprise attack, and have tremendous psychological impact.
We seem to have an almost primal fear of germ warfare. Above all, such weapons are exceedingly cheap. They are therefore very attractive to terrorists or belligerent nations. Many nations, including the USSR and Iraq, signed the 1972 Biological Weapons Convention which committed the signers to not develop or use them. Rumors abound that many nations have them, including those weapons that we mentioned.