The term "biotoxin" is sometimes used to explicitly confirm the biological origin. Biotoxins can be further classified, for example, as fungal biotoxins, microbial biotoxins, plant biotoxins, or animal biotoxins. Toxins produced by microorganisms are important virulence determinants responsible for microbial pathogenicity and/or evasion of the host immune response. Biotoxins vary greatly in purpose and mechanism, and can be highly complex (the venom of the cone snail contains dozens of small proteins, each targeting a specific nerve channel or receptor), or relatively small protein.
Biotoxins in nature have two primary functions:
- Predation, such as in the spider, snake, scorpion, jellyfish, and wasp
- Defense as in the bee, ant, termite, honey bee, wasp, and poison dart frog