Biotoxins are substances which are both toxic and have a biological origin. They come in many forms and can be produced by nearly every type of living organism: there are mycotoxins (made by fungi), zootoxins (made by animals) and phytotoxins (made by plants). Whilst some appear to have no advantage for the organism making them (they might be a waste product, for example), most are produced to help in two main activities  predation and defence against predation by other species, and so have very important roles in the life cycle of the organism. As we can see, biotoxins are varied in both function/mechanism and form.