Mad about Science: Venomous biology

By Breden Bobby
Reader Columnist

“In Africa, the saying goes ‘In the bush, an elephant can kill you, a leopard can kill you and a black mamba can kill you. But only with the mamba is death sure.’ Hence its handle, ‘Death Incarnate.’” 

— Daryl Hannah as Elle Driver, Kill Bill Vol. 2

Some of the most dangerous animals on planet Earth are among the smallest and most inconspicuous. Small critters loaded to the brim with potent killing chemicals that can incapacitate and kill in weeks, days, hours or in some cases even minutes.

It’s important to distinguish between a poisonous animal and a venomous animal. Poison dart frogs are poisonous, but they are not venomous. The black mamba is both. In order for a poison dart frog to kill you, you would have to handle one in the wild. A black mamba can inject you with poisonous compounds through its fangs and venom glands. Essentially, if it’s venomous, it comes with nature-made syringes to inject its toxins into your bloodstream.

The black mamba. Courtesy photo.

Bonus fact: Poison dart frogs stop being poisonous in captivity. The toxins are a heavy alkaline waste product secreted as a byproduct of the frog’s primary diet, which consists of ants and termites. Carefully maintained diets in captivity remove this waste compound from ever entering their system, thus eliminating their ability to poison humans.

Animal venom comes in a number of flavors. The three most common compounds are cytotoxins, neurotoxins and hemotoxins. Each of these can be found in a wide variety of snakes, though a small number of mammals and most jellyfish are capable of producing at least one of these.

Cytotoxin works by chemically disrupting the outer membrane of the cells it encounters. The membrane of a cell acts as a filter and housing for the contents of the cell, keeping harmful things out. You can almost think of a cell membrane as the walls and roof of a house. Cytotoxin interacting with the walls of this house is a lot like a tsunami sweeping through a neighborhood, indiscriminately tearing down roofs and walls and scattering the contents all over the place. 

Zoom out a little bit and this starts to look like necrosis, with skin and flesh dying and breaking down, rotting from the injection site outward. 

Puff adders harbor cytotoxins within venom glands in the back of the throat just below the snake’s brain. These glands come equipped with a compressor muscle that can tense up and squeeze the venom through a canal within the fang, leading to large amounts of venom being injected into a snake’s intended target.

Interestingly, the very thing that makes cytotoxin so scary may be the exact feature humans desire in order to develop effective cancer treatments when applied surgically.

Neurotoxins are among the most lethal of snake venoms on the planet. Cobras, mambas, kraits, taipans and sea snakes all harbor lethal neurotoxic venom. Neurotoxic venom directly attacks the nervous system of the prey, acting as a disruptor that blocks signals from the brain to muscles causing paralysis. This is especially bad when it is introduced into the bloodstream by way of the snake’s injecting fangs, and allowed to travel freely to the body’s organs. Many victims of a neurotoxic bite die of suffocation once their lungs become paralyzed and they can no longer breathe.

Hemotoxins attack red blood cells and cause a whole host of issues depending on the type of snake and the amount of venom injected. Rattlesnakes, adders, pit vipers and bush vipers all utilize hemotoxic venom. In some cases, hemotoxin causes blood to clot while it’s still in the veins and arteries, which causes stoppages to the circulatory system that eventually lead to cardiac arrest and likely death. 

Other forms of hemotoxin do the exact opposite, thinning the blood to an extreme degree and causing massive blood pressure fall-offs or blood leaking into the urine via the kidneys.

Snakes always get a bad rap for being venomous, but they’re hardly the only animal on the planet capable of delivering a venomous bite. When you’ve evolved not to have any legs or arms, you need a little extra something with which to defend yourself.

The southern short-tailed shrew, which inhabits the southeastern United States, has evolved with a specialized venom for killing its prey. A single bite carries enough potency to kill 200 mice — and while this sounds pretty scary, it shouldn’t be enough to kill an adult human, though it sure does hurt.

Perhaps the most venomous and lethal creature on the planet could easily be mistaken for a plastic bag floating on the waves. The box jellyfish carries a powerful venom that it injects with countless tiny nematocysts, which are microscopic structures with barbs and venom injectors. As a creature comes in contact with a box jellyfish, it gets caught in the tentacles, which are lined with these nematocysts that repeatedly sting the creature over the entire surface of its body. 

The jellyfish sting can be easily countered by wearing a layer of clothing such as a wetsuit or pantyhose over the skin. It has been discovered that the nematocysts are not activated by touch but by a chemical reaction with organic matter present on the skin or scales of most animals. Box jellyfish are actually capable of actively hunting prey.

You may be wondering how venomous creatures don’t poison themselves. Naturally, as the creature has evolved to contain these compounds, its natural defenses come pre-equipped to fight them off or nullify their effects when self-applied, such as a black widow spider eating an insect it just envenomed. That being said, it doesn’t make these animals immune to all forms of venom.

Stay curious, 7B.