Mycologist: Not only humans like mushrooms

PAP: What is eating our mushrooms?

Marta Wrzosek: First of all, mushrooms aren't ours. Fruiting bodies are formed so that mushrooms can reproduce and spread. It's worth remembering that they are independent entities, but they can also be tasty and nutritious. Therefore, mushrooms are of interest not only to humans but also to a wide variety of insects. Among those that are most troublesome to us are the larvae of midges.

But there are also larvae of beetles from the click beetle family, the so-called wireworms. The larvae of fly flies and wireworms differ significantly, making them easy to recognize. Wireworms, with their elongated bodies, are covered with a hard, brown chitinous shell and have three pairs of short legs. Wireworm larvae also make larger holes in mushrooms than the white, fat, and soft larvae of fly flies.

Moreover, the body of the wireworm and the fly is composed of so-called tagmas, separate segments, but the stiff chitinous covering of each tagma of the wireworm causes them not to writhe, but to vibrate in a way resembling toy snakes.

We encounter fly larvae much more frequently in mushrooms. They are common and very diverse. Wireworms are not very common in mushrooms because they are essentially predatory insects. However, if we see a small, two-centimeter-long brown string, we won't mistake it for a fly.

Moreover, if the flies attack the fruiting body of the fungus, there are plenty of these larvae, while the wireworm larvae are at most a few.

We can find fly larvae in mushrooms such as boletes, butter mushrooms, bay boletes, saffron milk caps, honey fungi, cabbage rolls – in short, in almost every mushroom we like.

PAP: What are these terrible creatures, these flies?

MW: The flies found in mushrooms belong to the family Mycetophilidae . These insects somewhat resemble mosquitoes. They are as slender as mosquitoes, but slightly smaller. They belong to the category of long-tailed flies. The very name of the family suggests that they are mushroom lovers.

They attack not only mushrooms but also bracket fungi. Among them is the common bracket fungus. One of the flies, belonging to the genus Trichonta, lays its eggs in the hymenophore layer, the place where spores are produced. When the larvae hatch, they create a web-like sheath that protects them and allows them to feed safely. When mature, they encase themselves in a cocoon and metamorphose within it. When the adult insects emerge from their cocoons, they mate on the fruiting body and then lay more eggs. These eggs are completely dependent on the fungi; without them, they wouldn't exist.

The fruiting body of the tinder fungus is only nibbled by flies. It can live for many years and support multiple generations of flies, while mushrooms attacked by flies deteriorate faster than fruiting bodies untouched by insects. In the case of flies developing in buttermilk or russula, it's crucial for the insects that fertilized females find a fruiting body that's very young, yet still offers a chance for the laid eggs to complete the entire larval cycle.

I saw swarms of flies circling the honey fungus just as the caps were beginning to open. The insects were waiting for the first opportunity to lay eggs among the gills.

In addition to flies and wireworms, mites also feed on mushrooms, but honestly, we don't have to worry about them much because mites are everywhere anyway, and we can't see them.

Springtails and rove beetles also contribute. Some rove beetles love honey fungi and many other wood-dwelling fungi. We can often spot them among their gills.

Springtails, on the other hand, readily feed on mycelium, but they also enjoy fruiting bodies. One springtail, the beautiful blue tetrodontophora bielanensis, loves puffballs, which humans generally don't eat, although young specimens are edible.

PAP: When is there a risk of encountering more worm-eating fungi: during drought or during rain?

MW: It doesn't matter whether there's a drought or rain - different insects like different weather conditions and have their own temperature optimums, so it depends on the nature of a given species of mushroom and insect, and not on the weather, whether the mushrooms will be worm-infested or healthy.

PAP: If we eat such a "mushroom worm", can it harm our health?

MW: Although it may sound controversial, the insects that colonize mushrooms are edible.

There's nothing to worry about; I haven't heard of any toxic insects living in mushrooms. So even if we happen to eat a wireworm, we'll simply absorb more protein. It's worth noting that a slight degree of redness is acceptable even in mushrooms approved for sale. Selling mushrooms with 10% redness is still legal.

However, there are also mushrooms that insects avoid. These include chanterelles, also known as fox mushrooms, about which Adam Mickiewicz writes in "Pan Tadeusz": "Mushrooms abounded: boys took dwarf mushrooms, so much praised in Lithuanian songs, fox mushrooms, which are a symbol of maidenhood, because maggots don't eat them, and strangely enough, no insects land on them."

Some species of mushrooms defend themselves against insects by producing mucus, compounds that are toxic to insects, or unpalatable, or even by their consistency—either too firm or hard and stringy. Macrolepiota also defends itself against worms, but bay boletes do not.

There are also mushrooms that are particularly susceptible to maggots. These include the red toadstool. This is an exceptionally tasty species of mushroom – but the biggest challenge with picking them is getting there before the maggots do.

PAP: What does it depend on?

MW: How fungi cope with insects depends on their structure and the species of insect that wants to colonize them. For example, the kite is avoided by flies that lay eggs near the root – its stem is hollow inside, and the outer hyphae of the stem are fibrous – the larvae have nothing to eat.

Wireworms also always enter the mushroom from the bottom, so they're easier to find in the stems than in the caps. Boletes, with their incredibly tempting stems, are readily attacked by beetles. But boletes are also large mushrooms, so relatively large wireworms fit comfortably inside them. Wireworms carve tunnels at least one millimeter in diameter into the stems of the boletes and gnaw their way upward.

There are also flies that attack the mushroom from the cap, so the larger and juicier the cap, the more desirable and crowded it is. Small, ephemeral mushrooms don't harbor insects, but nematodes, mites, and springtails will readily feed on them.

PAP: What should we do if we find a wormy mushroom?

MW: If we find a mushroom that is only slightly red, just cut out the most infected part and there is nothing stopping us from using the rest in the kitchen to prepare a dish.

But if there are a lot of these larvae, it's better to throw the mushroom away. You can also try drying these worm-infested specimens in a special mushroom dryer. I guarantee that the larvae will escape. And if such well-prepared dried mushrooms are sealed in an airtight container, there shouldn't be any problems.

However, what you definitely shouldn't do is leave a slightly worm-infested mushroom "to be processed later." Before you know it, all the other mushrooms, even the previously "healthy" ones, will be full of wriggling worms.

PAP: So maybe it's better to buy mushrooms than to fight worms?

MW: You shouldn't be overly afraid of insects inhabiting mushrooms; it's also worth remembering that, according to current regulations, mushrooms that are slightly worm-infested are allowed for trade, and regulations are soon to come into force that will further increase the permitted percentage of redness.

Therefore, the best defense against worms is to immediately heat-treat mushrooms – sauté, fry, boil, or dry them. And don't store dried mushrooms in a damp environment – ​​moisture is the perfect breeding ground not only for various invertebrates but also for molds and bacteria.

And one more thing to consider: when the larva eats the fungus, it uses some and excretes the rest. Poop also consists of mycelium, but it's enriched with bacteria, which only high temperatures can kill.

PAP: So where to pick mushrooms?

MW: If anyone's looking to go mushroom picking in the next few days, I recommend Masuria, Western Pomerania, the Tuchola Forest, and Kujawy. I'd avoid eastern Poland for now, but its time will come soon. The rains are slowly approaching, and with them, the mushrooms.

Interviewed by: Mira Suchodolska (PAP)

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