Toxicity: fears and reality

By Daniel Butler, forager and author

There is a fascinating divergence in attitudes to fungi on either side of the Channel. Every autumn crowds stream out of French, Italian and Polish cities to rummage in the woods for delicious mushrooms. In Britain, however, there is an almost universal conviction that death lurks within every wild fungus – or toadstool as we prefer to call them. This prejudice is statistically ridiculous, but bears scrutiny to dispel the myths.   

Fly agaric may be the classic ‘toadstool’, but is relatively harmless in reality

(Image: Author’s own)

No one knows exactly how many visible mushroom species there are in Britain, but estimates range from 12 - 15,000. Of these about 200 are edible while roughly 30 are seriously poisonous. So were you so silly as to play fungal roulette, you would be three times as likely to enjoy the experience as suffer harm. You would be some 50 times more likely to experience nothing more interesting than a chewing exercise. Clearly you must always identify everything with certainty before you eat and should also be at least vaguely familiar with those you must avoid at all costs. Other than this, given an ounce of common sense, the risks are minimal.

There is a Danish study which gives a medical perspective to fungal toxicity. It analysed mushroom fatalities around the globe and found that in practice almost all are down to just five species. These are the false morel (Gyromitra esculenta); death cap (Amanita phaloides); destroying angel (Amanita virosa); and the deadly and fool’s webcaps (Cortinarius rubellus and C. orellanus).

False morel - deadly when raw

(Image: Author’s own)

The false morel is certainly extremely toxic when raw, but utterly delicious when thoroughly cooked. No such treatment will render the other four safe. The death cap is responsible for more fatalities than all the others put together, killing by destroying the liver and kidneys. It is also common in temperate woodland and accounts for multiple deaths every year – at least elsewhere.

Death cap - responsible for 90% of global fatalities

(Image: Charles Pottinger)

I can find only three adult deaths from fungal poisoning in the UK over the past century with the best documented an Isle of Wight lady who mistook death caps for cultivated paddy straw mushrooms in 2007. Its close relative, the destroying angel is just as toxic, but is much less common and also less liable to be confused with an edible species.  

The deadly and fool’s webcaps are also very poisonous. Both have been responsible for deaths on the Continent and several near-fatal incidents in Britain. Most famously this includes Nicholas Evans, author of The Horse Whisperer, who nearly killed himself; wife and hosts on a Scottish family holiday.

Deadly webcap growing in a children’s playground

(image: Author’s own)

Obviously, there are other potentially deadly mushrooms, but in practice the risks are low. In many cases the poisoning can be reversed with medical help. Other species prompt the body’s own natural defences to step in: some taste so unpleasant that no one would eat a fatal dose or the victim quickly vomits to expel the toxins. 

In addition to the outright poisonous, there are a few species – most notably the brown roll rim (Paxillus involutus) which can cause cumulative kidney and liver damage in susceptible individuals. This is rare, but it can be fatal.

There are also species which are mildly toxic or indigestible when raw, but make good eating when cooked. These include honey fungus (Armillaria mellea), blushers (Amanita rubescens) and blewits (Lepista spp.). Ironically, it is our innate fear of mushrooms which leads to most British A&E admissions. Would-be foragers, tentatively searching their first wild fungus, seek the apparent security of the field mushroom (Agaricus campestris) which so closely-resembles its cultivated cousins on the supermarket shelf. Unfortunately, there is another Agaricus, the yellow stainer (A. xanthodermus), which looks identical apart from bruising yellow and smelling of carbolic or phenol. Eating this can produce violent vomiting and diarrhoea in about half the population. It is never fatal.

The British (particularly the press) take fungal risks completely out of proportion

(Image: The Times, 5/10/14)

Bear in mind too that mushrooms contain relatively high levels of protein and even very edible species can upset some stomachs. All too often people treat powerfully-flavoured wild mushrooms just like a blander cultivated version. In reality they should be treated more as a herb or spice than a major ingredient – particularly on the first outing. Every species of mushroom, however delicious, will disagree with someone, somewhere. So it’s always best to stick to modest quantities and to cook: particularly for the first time. As a rule of thumb about 2oz (50g) per person is a good portion.

So while eating mushrooms is not without risk, much the biggest danger is indigestion. This won’t be fatal, but will certainly be memorable. Any Briton who feels ill after eating a wild mushroom will be tormented not merely by a prolonged period in the loo, but by psychological anguish as they imagine imminent and certain death.