This mushroom will kill you before you know what’s happening - Michael Beug

It is said that to secure Nero’s succession as fifth emperor of Rome, his mother, Agrippina, discreetly assassinated her own husband. The murder weapon? A handful of death cap mushrooms.

Humans have clearly known about the toxicity of death caps for millennia. Yet these mushrooms continue to pose a significant threat to unsuspecting foragers and mushroom hunters throughout the world. Today, death caps are responsible for more than 90% of all mushroom related deaths, killing upwards of 100 people each year.

So, what makes this one species of mushroom so dangerous? Despite their danger, death caps, known scientifically as Amanita phalloides, look relatively unassuming. They emerge enclosed in a white egg-like membrane that ruptures, leaving a cup-like sac at the stem’s base.

Mature mushrooms are domed with white or greenish yellow caps measuring anywhere from 4 to 16 centimeters in width. And just half of a cap can contain enough toxin to kill an adult. While death caps produce several types of toxins, one class, amatoxins, are by far the most dangerous.

They’re hearty compounds, not easily destroyed by cooking, freezing, or drying. And if ingested, amatoxins easily pass through the intestinal wall to enter the bloodstream and wreak havoc on multiple systems. Their main method of destruction is blocking the action of enzymes called RNA polymerases.

These enzymes are essential to the body, as they allow the cells to build the proteins they need to function. For example, amatoxins inhibit the production of blood clotting compounds, which can cause a person to bleed out. In the kidneys, they slowly obstruct the body’s ability to regulate fluids and produce urine.

But they’re perhaps the most damaging to the liver. The liver is where waste products, including toxins, are filtered out of the blood, so amatoxins naturally accumulate. This toxin bombardment blocks the turnover of new proteins, causing these liver cells to die.

Over time, this can lead to liver failure and eventually death. One puzzling death cap mystery that continues to elude scientists is understanding exactly what benefits poisonous amatoxins provide to the mushroom. Amatoxins are secondary metabolites, meaning they’re not essential for mushroom growth or survival.

And grazing rabbits, rodents, and humans are often a highly effective mode of spore dispersal for other mushroom species. So, what’s the evolutionary advantage of poisoning them? And amatoxins aren't exclusive to death caps.

They’re also produced by several other species of mushrooms, from the genera Galerina and Lepiota. Yet unlike death caps, poisonous Galerina and Lepiota species cause relatively few human deaths. The reason for this is two-fold.

First, these Galerina and Lepiota mushrooms are quite distinguishable, whereas death caps, especially young ones, can easily be mistaken for other edible mushrooms, like straw mushrooms or puffballs. Further, death caps have a relatively large range. While native to Europe, they're now found on every continent except Antarctica.

Death caps form close symbiotic relationships with European hardwoods and conifers. Throughout the 20th century, as these trees were planted in colonized regions around the world, death caps covertly tagged along. Thankfully, if a victim of death cap poisoning is properly treated soon after ingestion, up to 90% of patients will survive.

Treatment doesn’t require any sort of special antidote— a continuous, aggressive IV drip is often enough to flush the toxins from the blood. However, not all doctors know how to properly treat or recognize death cap poisoning. Initial symptoms can look similar to other types of food poisoning.

To add to the confusion, because amatoxins build up slowly in the liver, the most dire symptoms often don’t appear until days after consumption. Despite growing medical knowledge, it’s important that mushroom hunters throughout the world learn how to properly recognize and avoid this deadly species. So, if you ever find yourself foraging, remember to be on guard, and when in doubt, it’s always best to toss it out.