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Fungifungus

Predatory fungi

A fungus with no muscles closes a ring around a worm in a tenth of a second — and it knew to build the ring because it was listening to the worms talk.

Some soil fungi hunt animals. They build traps — including rings of three cells that inflate in about a tenth of a second to hold a struggling worm — and they only build them when prey is around, because they detect nematodes by intercepting the pheromones the worms use on each other.

The reason this belongs on a site about predation is that it removes every feature people assume predation requires. There is no nervous system here, no muscle, no sense organ and no movement in the ordinary sense. There is a fungus in soil, and it does the whole sequence: it detects that prey is present, it builds apparatus in response, it captures a living animal, and it digests it from the inside. The traps come in several designs, arrived at independently by unrelated fungi. Some are sticky networks that a worm blunders into and cannot pull free of. Some are adhesive knobs that detach and ride on the animal. And the most arresting is the constricting ring: three cells forming a loop that a nematode swims through, which then inflate — roughly tripling in volume in about a tenth of a second — and hold the worm while hyphae penetrate its cuticle. That is genuinely fast movement, achieved without muscle, by an organism most people picture as passive. What makes it predation rather than opportunism is that the traps are built to order. These fungi live perfectly well as decomposers, and produce traps only under conditions that favour hunting — which raises the question of how a fungus knows a worm is nearby. The answer is the best part of the subject. Nematodes signal to one another with small molecules called ascarosides, used for aggregation and development. The fungi detect those molecules and build traps in response — and they do it when given the purified compounds alone, with no worm present anywhere. The prey animals are talking to each other, and something in another kingdom is listening and setting a trap. It is exactly the eavesdropping that turns up in bird alarm calls, relocated to soil and conducted between a fungus and an animal.

Early coverage · 55% complete · reviewed 2026-09-03

What this page covers

Nematode-trapping has arisen independently in several unrelated fungal groups, with different trap designs in each. Other fungi attack nematode eggs or use adhesive spores, which are separate strategies.

Often confused with: Decomposers, which these fungi also are — predation is a mode they switch into; Parasitic fungi, which live in a host rather than capturing it; Carnivorous plants, which solve a similar nutrient problem by a completely different route

Quick facts

Genuine predation
Detect, trap, capture, digest — with no nervous system
The constricting ring
Three cells inflating in about a tenth of a second
How it knows
By detecting the pheromones nematodes use on each other
Not full-time
They decompose too, and build traps only when hunting pays

Predation without any of the equipment

No muscle, no nerves, no senses — and the whole sequence performed anyway.

Some soil fungi hunt. They build traps — including rings that inflate in about a tenth of a second to hold a struggling worm — and they build them only when prey is present, not all the time.

Established

Specialists would state this without hedging. Multiple independent lines of evidence agree.

Nematophagous fungi produce specialised capture structures — adhesive networks, adhesive knobs, and constricting rings that close by rapid cell inflation within approximately a tenth of a second — followed by cuticle penetration, infection bulb formation and digestion by trophic hyphae. Trap formation is induced rather than constitutive.

Who this applies to
Soil fungi across several unrelated groups that capture nematodes; the trap types differ between them.
Studied in
Fungi, Nematoda
Why we rate it this way, and what the caveats are
EstablishedHigh confidence

The structures, the capture and the digestion are directly observable in culture, and trap induction can be manipulated experimentally.

How far it can be extended

Trapping structures have arisen independently in unrelated fungal lineages and have been characterised across them.

Caveats

  • These fungi are facultative predators: they live perfectly well decomposing dead material, and hunt when conditions favour it. Predation is a mode rather than an identity.
  • Almost all observation is on culture plates; behaviour in structured soil is far harder to watch.

Still unanswered

  • How the ring generates the pressure to inflate that fast, in a cell wall that must also be strong enough to hold a struggling animal.

Last reviewed 2026-09-03

The evidence (2 studies)
Trap designs, arrived at independently
TrapHow it holds the wormWhat happens next
Adhesive networkA three-dimensional sticky mesh the worm blunders intoHyphae penetrate where contact was made
Adhesive knobA sticky cell that detaches and travels on the animalPenetration from the attached knob
Non-constricting ringThe worm wedges itself passing throughPenetration through the cuticle
Constricting ringThree cells inflate in about a tenth of a secondThe worm is held while hyphae enter

The last row is the one worth sitting with. A fungal cell wall is a rigid structure; making three of them triple in volume in a tenth of a second, in a coordinated way, on contact, is a mechanical problem that would be impressive in an animal. How the pressure is generated fast enough — and how a wall stiff enough to hold a struggling nematode also expands that quickly — is not fully explained.

It builds traps because it heard the worms

The prey are signalling to each other, and something else is listening.

The fungus knows when worms are near because it listens to them. It builds traps in response to the chemical signals nematodes use to communicate with each other — with no worm present at all.

Well supported

Good evidence backs this, though some details remain open.

Nematode-trapping fungi initiate trap morphogenesis in response to ascarosides, the pheromones nematodes use for intraspecific signalling. Purified ascarosides induce trap formation in the absence of nematodes, in a concentration-dependent manner, with different fungal species responding to different ascarosides.

Who this applies to
Demonstrated in nematode-trapping fungi responding to nematode ascarosides in culture.
Studied in
Arthrobotrys, Caenorhabditis elegans, Fungi
Why we rate it this way, and what the caveats are
Well supportedHigh confidence

A clean experimental manipulation: purified compounds, no animals present, and traps produced anyway — which isolates the cue from every other property of a nematode.

How far it can be extended

Several trapping fungal species respond to ascarosides, though which compounds they respond to differs between them.

Caveats

  • Purified compounds in culture isolate the cue at the cost of realism; soil contains many signals at once.
  • Species differ in which ascarosides they detect, so this is a family of related mechanisms rather than one.

Still unanswered

  • Whether nematodes have evolved any countermeasure — signalling less, or differently, where trapping fungi are common.

Last reviewed 2026-09-03

The evidence (2 studies)

How we know

The chemical without the worm

A trapping fungus builds traps when nematodes are present. Is it responding to the animals themselves, or to the chemicals they release?

Trap-forming fungi were exposed to purified ascarosides — the pheromones nematodes secrete to communicate with each other about population density and development — with no nematodes present at all. Trap formation was scored against unexposed cultures, and across several fungal species and several ascaroside structures.

What happened

The purified pheromones induced trap formation on their own. The response varied with the ascaroside structure and with the fungal species, and did not require the worms to be there.

What it shows

That the fungus is eavesdropping. Nematodes use these molecules to signal to each other, and a predator with no sense organs has evolved to intercept them — and to build an expensive structure only when the signal says prey is about. It is the same interception logic as an eavesdropper on an alarm call, between kingdoms and in soil.

What it does not show

It does not establish that ascarosides are the only cue, or the main one in soil, where many chemicals are present at once. It also does not identify what the fungus detects them with, which is unresolved.

The controls — what makes this evidence rather than a story
  • No nematodes in any exposed culture, so trap formation cannot be a response to contact or movement.
  • Solvent-only cultures, separating the pheromone from the vehicle it was delivered in.
  • Multiple fungal species tested, distinguishing a general response from a quirk of one strain.

From Nematode-trapping fungi eavesdrop on nematode pheromones

Diagram

Four ways to hold a worm

The trap repertoire, and the fact that none of it is kept standing when there is nothing to catch.

Four ways to hold a wormAdhesive networkSticky loops of hyphaeAdhesive knobA single sticky bulbNon-constricting ringA loop the worm jams inConstricting ringThree cells inflate, ~0.1 sBuilt only whenprey is detected —not kept standing.No muscle, no nerve, no sense organ anywhere in this.
The same explanation in words

Four kinds of trap are listed in order. An adhesive network of sticky hyphal loops; a single sticky knob; a non-constricting ring the worm forces itself into and cannot reverse out of; and a constricting ring, whose three cells inflate in about a tenth of a second to hold a struggling animal. A note beside them records that traps are built only when prey is detected, rather than maintained permanently, and a closing line points out that none of this involves muscle, nerve or sense organ.

The design is what makes this decisive. If traps appeared when nematodes were present, the fungus might be responding to movement, to touch, to disturbance, or to any of a hundred things a worm brings with it. Purified ascarosides bring none of those — there is no animal in the dish — and the traps appear anyway. Whatever else the fungus may also use, it is demonstrably reading the pheromone.

This puts the fungus in the same position as a nuthatch listening to chickadee alarm calls: a signal evolved for one audience, intercepted by a receiver it was not meant for, and used against the signaller. The difference is that here the eavesdropper is in another kingdom and the consequence is fatal.

And then it answers back

Deception, by something with no nervous system, on an animal that has one.

The fungus does not only listen. Trap-bearing cultures release volatiles resembling nematode sex pheromone and food odours, and worms follow them in — deception, practised by something with no nervous system.

Well supported

Good evidence backs this, though some details remain open.

Trap-bearing Arthrobotrys oligospora cultures emit volatile compounds, including analogues of nematode sex-pheromone and food-associated odours, that elicit chemotaxis in nematodes through identified olfactory pathways. Volatile profiles differ between fungal species in ways corresponding to their prey.

Who this applies to
Demonstrated in laboratory chemotaxis assays for particular fungi and mostly one well-studied nematode.Do not extend this beyond the taxa listed — the popular version over-reaches.
Studied in
Arthrobotrys, Nematoda
Why we rate it this way, and what the caveats are
Well supportedModerate confidence

The attraction is measured and the nematode sensory pathway identified. How much the lure matters in soil, at soil distances, is not established.

How far it can be extended

Volatile profiles differ between fungal species; the lure is specific rather than a general property of trapping fungi.

Caveats

  • Plate assays measure attraction over centimetres; a soil pore is a different problem.
  • Whether the resemblance to sex pheromone is mimicry in the evolutionary sense or a coincidence of shared chemistry is not settled by attraction alone.

Still unanswered

  • Whether nematodes exposed to trapping fungi over generations become less responsive to the lure.

Last reviewed 2026-09-03

The evidence (2 studies)

How we know

The smell of a mate that is not there

A trapping fungus builds traps when worms are near. Does it also do anything to make worms come near?

Volatiles released by trap-bearing fungal cultures were collected and chemically identified. Nematodes were then given a choice, in chemotaxis assays, between those volatiles and controls. Mutant nematodes with particular olfactory pathways disabled were tested alongside normal ones, and several fungal and nematode species were compared.

What happened

Trap-bearing cultures attracted nematodes, and among the volatiles were compounds resembling nematode sex pheromone and food-associated odours. Attraction depended on identified olfactory pathways, and the volatile profiles differed between fungal species in ways matching their prey.

What it shows

That the fungus is not only listening but answering. It reads the chemicals nematodes use to talk to each other, and it emits chemicals that read to a nematode as a mate or a meal. That is deception in the strict sense — a false signal, tuned to a specified receiver — produced by an organism with no nervous system at all.

What it does not show

Attraction on a plate over centimetres does not establish how much the lure matters in soil, where the geometry and the chemical background are entirely different. Whether the resemblance to sex pheromone is evolved mimicry or shared chemistry is also not settled by attraction alone.

The controls — what makes this evidence rather than a story
  • Cultures without traps, separating the lure from the ordinary smell of a growing fungus.
  • Olfactory mutants, which show that the attraction runs through specific sensory routes rather than being general movement.
  • Multiple nematode species, distinguishing a tuned lure from something all worms drift towards.

From Nematophagous fungus Arthrobotrys oligospora mimics olfactory cues of sex and food to lure its nematode prey

Diagram

Two signals, going opposite ways

One signal intercepted, another sent back — in opposite directions.

Two signals, going opposite waysNematodesTalking to each otherTrapping fungusNo nervous systemPheromones, interceptedVolatiles that read as mate or foodReading a signal: eavesdropping. Sending a false one: deception.The attraction disappears when the worm’s olfactory pathways are disabled,which is what makes it a claim about a receiver rather than a story.
The same explanation in words

Two boxes face each other: nematodes on the left, described as talking to each other, and a trapping fungus on the right, described as having no nervous system. An arrow runs left to right labelled as pheromones being intercepted, and a second arrow runs right to left labelled as volatiles that read to a nematode as a mate or as food. The caption below distinguishes the two: reading a signal is eavesdropping, sending a false one is deception. A final note records that the attraction disappears when the worm’s olfactory pathways are disabled, which is what makes this a claim about a specified receiver rather than a story.

Put the two chemical results side by side and the exchange is complete. The fungus reads the molecules nematodes release to inform each other about density and development, and builds traps when the reading says prey is about. Then it releases volatiles that a nematode’s olfactory system interprets as a mate or as food, and the worm walks towards them. Signal read, false signal sent — which is the definition of deception used everywhere else on this site, applied to an organism with no brain to do the deceiving.

The receiver principle earns its keep here. Whether these volatiles smell like anything to a person is irrelevant; what matters is that they engage identified olfactory pathways in the specified receiver, and that disabling those pathways removes the attraction. That is how a claim about deception is made testable rather than anecdotal.

Fed to cattle on purpose

The practical test of whether the biology is understood.

Spores of a trapping fungus fed to grazing livestock survive the gut, germinate in dung, and hunt the parasite larvae developing there — cutting the number that reach the pasture.

Well supported

Good evidence backs this, though some details remain open.

Duddingtonia flagrans chlamydospores administered to grazing livestock pass through the digestive tract intact and germinate in faeces, forming traps that reduce the number of infective nematode larvae migrating onto surrounding herbage. Effect sizes vary with dose, strain and conditions.

Who this applies to
Grazing livestock parasites with a free-living dung stage; not applicable to parasites lacking one.
Studied in
Duddingtonia flagrans, Nematoda
Why we rate it this way, and what the caveats are
Well supportedModerate confidence

Repeatedly demonstrated, with effect sizes varying widely between trials and conditions.

How far it can be extended

Demonstrated in trials across several livestock species and settings.

Caveats

  • It reduces new infection from pasture; it does nothing to worms already inside an animal.
  • The long-term behaviour of an introduced fungus in a pasture ecosystem is not fully characterised.

Still unanswered

  • How much of the variation between trials is fungal strain, and how much is weather and dung ecology.

Last reviewed 2026-09-03

The evidence (1 study)

The life cycle is what makes this work. Parasitic worms of grazing livestock spend part of their lives outside the animal: eggs pass out in dung, develop there, and the infective larvae migrate onto the surrounding grass to be eaten again. Spores of a trapping fungus fed to the animal survive the gut, germinate in that dung, and hunt the larvae during exactly the stage that has to happen outside a host.

It is worth being clear about what it does not do. It kills nothing inside the animal, so it is a way of lowering the rate of new infection from pasture rather than a treatment. The interest is that it works by a completely different route from the drugs, which matters where resistance to those drugs is spreading — and that it depends on nothing more exotic than a soil fungus doing what it already does.

Why a decomposer would take up hunting

Because dead plant material is short of one thing in particular.

Wood and leaf litter are rich in carbon and poor in nitrogen, and a fungus living on them has plenty of energy and not enough of the element it needs for proteins. A nematode is a small package of nitrogen that walks past. That is the same accounting that produced carnivorous plants — organisms with ample energy and a nutrient shortage, solving it by catching animals — and it is why both strategies concentrate in nutrient-poor places.

The same problem, solved twice

  • Carnivorous plants

    Energy in hand, nitrogen scarce — and animals as the solution

  • Fungi

    What a fungal body actually is

  • Predation

    The sequence, performed here without any of the usual equipment

  • Decomposition

    The job these fungi do the rest of the time

The research behind this page

5 studies, newest first. Each one has a page explaining what it found and what it could not show.

2017eLife

Nematophagous fungus Arthrobotrys oligospora mimics olfactory cues of sex and food to lure its nematode prey

Trap-bearing cultures released volatiles that attracted nematodes, including compounds resembling nematode sex pheromone and food-associated odours.

2013Current Biology

Nematode-trapping fungi eavesdrop on nematode pheromones

The fungi produced traps in response to the pheromones alone, without any nematode present.

2004Mycologist

Morphogenesis in the nematode-trapping fungus Arthrobotrys oligospora: an extensive plasticity of infection structures

Traps are formed in response to the presence of nematodes rather than produced continuously.

2000Parasitology

Prospects for controlling animal parasitic nematodes by predacious micro fungi

Fungal spores surviving gut passage and germinating in dung substantially reduced the numbers of infective nematode larvae migrating onto surrounding pasture in multiple trials, with effects varying by dose, fungal strain and conditions.

1964Science

Nematode-trapping fungi

Several unrelated soil fungi produce specialised structures for capturing nematodes.

This page is a stop on a longer route

A guided journey reads several subjects in a deliberate order, with an argument for why one follows another. You can join in the middle.

Where to go from here

Each of these follows from something on this page — a relationship in the evidence, a claim people ask about, or the next mechanism along.

How complete this page is, and what it is still missing

NatureHQ publishes its own gaps. This page is at 55% completeness against what we would call a finished subject, and was last reviewed on 2026-09-03. It carries 4 claims and answers 5 mapped search questions.

  • no research from the last few years is attached — check for newer work
  • no popular claim about this subject has been checked yet
  • How a constricting ring generates enough pressure to close that fast is not fully explained.
  • Almost all observation is from culture plates; behaviour in structured soil is largely unwatched.
  • Whether nematodes have evolved any counter to being eavesdropped on is unknown.