Venom

Venom, also known as a zootoxin, is a biological substance produced by animals. It is actively delivered to another organism through a wound. This delivery happens via a bite, a sting, or a similar action. The process of injecting this toxin is called envenomation.

It is important to distinguish venom from other substances. Poison is a toxin that is passively delivered. A creature might ingest, inhale, or absorb poison through its skin. Toxungen are also different because they are transferred to an external surface via a physical mechanism. Venom is a specialized tool used by both predators and prey across many environments.

Venom works through several distinct classes of toxins that target different biological systems. Neurotoxins primarily affect the nervous systems of animals. These often act as ion channel toxins and are found in mambas, black widow spiders, and cone snails. Myotoxins damage muscles by binding to a specific receptor. These small, basic peptides are common in the venom of rattlesnakes and certain lizards. Cytotoxins are capable of killing individual cells. These are found in the apitoxin of honey bees and the venom of black widow spiders.

A subclass of cytotoxins is necrotoxins, which cause necrosis, or death, in the cells and tissues they encounter. Finally, haemotoxins work by disrupting the way blood clots.

Because many venoms are complex mixtures, they can contain many different types of toxins at once. This complexity allows the venom to be highly efficient. For example, some venoms contain phospholipases, which are enzymes that can affect calcium signaling. Snake venoms are particularly complex. They may contain proteases that hydrolyze protein peptide bonds. They can also contain nucleases that hydrolyze the phosphodiester bonds of DNA. These various components can cause a wide range of symptoms in a victim. These symptoms include pain, swelling, tissue necrosis, low blood pressure, convulsions, and even kidney failure or death.

Venom has appeared across a massive variety of life forms through convergent evolution. This means that different groups of animals evolved the trait independently. In fact, venom usage has evolved independently at least 104 times across 8 different phyla.

Some animals even acquire their toxins from external sources. Some species have been shown to get venom toxins from associated microbes. These microbes may even live inside the animal's venom apparatus. This evolutionary process is driven by active selection. Multigene families encode these toxins, creating diverse molecules with very specific functions. This allows venom to adapt to the specific prey or environment of the animal.

Many different taxonomic groups utilize venom. Arthropods like spiders use fangs on their chelicerae to inject toxins. In bees and wasps, the stinger is actually a modified ovipositor, which is an egg-laying device.

Some invertebrates, like the box jellyfish, possess some of the most dangerous venoms in the ocean. Among vertebrates, there is a huge variety of venomous species. There are about 450 species of venomous snakes. Many fish are also venomous, including over 300 species of scorpionfish. Even some mammals possess venom. This includes the male platypus, which evolved venom glands from modified sweat glands. Other mammals like the solenodon and the vampire bat also use venom.

In nature, the relationship between venomous animals and their targets often creates a "chemical arms race." This is a form of coevolution between predators and prey. As predators become better at using venom, the surviving prey develop resistance. This resistance allows prey to survive, but it also allows predators to move into new ecological niches. For example, the California ground squirrel has developed varying degrees of resistance to the Northern Pacific rattlesnake. Similarly, the kingsnake of the Americas has evolved resistance to the venom of snakes like the copperhead.

Some animals, like the clownfish, have developed an obligatory symbiosis with venomous sea anemones by becoming resistant to their stings.

While venom can be dangerous to humans, it is also a vital tool for modern medicine. This field of study is known as venomics. Scientists are investigating how venom proteins can treat various medical conditions. For instance, snake venom proteins are used to treat thrombosis, arthritis, and some cancers. The venom of the Gila monster contains exenatide, which is used to treat type 2 diabetes. Additionally, solenopsins from fire ant venom have shown potential for treating psoriasis. In 2013, envenomation resulted in 57,000 human deaths, which is a decrease from 76,000 deaths in 1990. With over 173,000 species using venom, the potential for pharmaceutical discovery remains enormous.