The fungus that listens and lies
When nutrients are scarce, the predatory fungus Arthrobotrys oligospora can transform ordinary hyphae into adhesive traps for nematodes. The change is not automatic. Nematode-derived chemicals help trigger it.
Some of those chemicals are ascarosides, a large family of small molecules used throughout nematode life. Different ascarosides help regulate development, mating, aggregation, dispersal, and other behaviors. To another nematode, an ascaroside may participate in a social or developmental signal. To the fungus, it can be evidence that prey are nearby. Experiments showed that several nematode-trapping fungi form traps in response to ascarosides under nutrient-limited conditions; later work identified fungal G protein-coupled receptors and downstream cAMP–PKA signaling involved in sensing ascarosides and other nematode-derived cues.[1]
The fungus does more than listen. It also emits volatile chemicals that attract nematodes toward it. One of the strongest is methyl 3-methyl-2-butenoate, or MMB. A 2017 study found that MMB attracts adult females or hermaphrodites in several Caenorhabditis species, interferes with mating in one tested species, and draws worms through olfactory pathways toward a predator that is better at catching animals that follow the odor.[2]
At the time, the researchers could only infer that MMB resembled a sex pheromone. A 2026 follow-up supplied an endogenous source: adult male Caenorhabditis remanei produce MMB at levels that attract C. remanei females. The compound also attracts C. elegans hermaphrodites, although the investigators did not detect it in C. elegans males. In that second species, the evolved relation behind the attraction remains unresolved.[3]
One predator is therefore exploiting two distinct chemical systems. Nematode ascarosides are prey-derived cues that help tell the fungus when nematodes are nearby. MMB is a sexual signal when male C. remanei produce it and a counterfeit lure when the fungus does. “Listening” and “lying” are shorthand: no conscious fungal scheme is required. The mechanisms are receptors, metabolites, neurons, development, and selection.
What, then, makes a chemical a signal in one relation, a clue in another, or a counterfeit when produced by a different organism?
Signals, cues, and counterfeits
Biologists use several overlapping definitions of a signal. On one influential evolutionary account, a trait counts as a signal when its production evolved partly because it affects a receiver, and the receiver’s response evolved in relation to that trait. A cue, by contrast, is useful to a receiver even though the feature did not evolve in order to affect that receiver. A footprint can reveal an animal’s route without having been left as a report.[4]
This distinction has a long history in chemical ecology. The same substance may function as a pheromone within one sender–receiver relation and as a kairomone—a cue beneficial to another receiver—in a different one. The label does not attach to the molecule in isolation.[4]
That makes the fungal system easier to describe. Male-derived MMB participates in a sexual signaling relation in C. remanei. Nematode ascarosides detected by the fungus are cues from the fungus’s perspective: their production need not have evolved to help a predator locate its prey. Fungus-produced MMB is aggressive signal mimicry or a manipulative input: the predator reproduces a carrier that already recruits attraction in its prey.[5]
The fungus also illustrates two different routes into another species’ signaling world. An eavesdropper exploits a carrier that the original organism already emits. A mimic instead produces an input that recruits a receiver’s existing response. These strategies do not require the same receptors, molecules, or evolutionary history; they are united only by their dependence on causal relations that a third party can enter.
It helps to distinguish four levels. First is the physical carrier: MMB, an ascaroside, a flash, a sound. Second is a statistical relation: observing the carrier reduces uncertainty about something else. Third is an evolved signal relation: production and response have been shaped in relation to one another. Fourth is the semantic gloss supplied by an observer—“mate,” “prey nearby,” “danger”—which summarizes what the carrier lets a receiver discriminate or do. These distinctions are analytical tools, not a universally accepted field-wide taxonomy. They keep us from imagining meaning as cargo sealed inside a molecule.[5]
None of this makes the carrier irrelevant. Molecular shape, volatility, persistence, amplitude, and spatial range constrain which organisms can detect or reproduce it. The relation does not float free of physics; it is built from physical properties plus receiver architecture and evolutionary history. The claim is only that chemistry by itself does not tell us whether a carrier is functioning as signal, cue, or mimic in a particular ecological relation.
This is the point of saying that signals are not addressed letters. It is not that biological signals lack targets. Many are confined to a tissue, delivered by contact, detectable only at close range, or recognized by a narrow receptor and a particular downstream circuit. Some work only when several inputs arrive together or when the receiver is in the right physiological state.
The narrower claim is that the carrier itself does not contain context-independent proof of who produced it or which receiver should respond. Targeting and source discrimination are built from bodies, receptors, environments, timing, and evolutionary history. Because they are built, they can sometimes be intercepted, copied, blocked, or made harder to exploit.
Nor does “relational” mean that receivers arbitrarily assign meaning. Signal production, receiver discrimination, unintended audiences, and countermeasures alter one another’s selection pressures. Eavesdroppers can favor quieter signals; mimicry can favor better discrimination; a once-reliable signal can lose reliability in a changed ecological network. The relation is causal and coevolutionary, not merely interpretive.[4][6]
Forging the reply
The clearest counterfeits are sometimes visible without chemistry.
Many fireflies identify mates through species-specific flash exchanges. A male Photinus produces a characteristic pattern while flying; a receptive female answers from vegetation after an appropriate delay. The male turns toward the reply.
Females of the predatory genus Photuris can enter that exchange. They answer Photinus males with flashes resembling the replies of Photinus females. A male approaches what appears to be a potential mate and is instead captured and eaten. James Lloyd later showed that Photuris versicolor used distinct reply patterns to attract males of four prey species; in his observations, females seldom answered more than ten males without catching one.[7]
This is aggressive mimicry in a particularly legible form. The predator does not need to reproduce the female’s body or understand the flash as a human would. It needs to produce enough of the relevant stimulus, at the relevant time, to recruit the male’s existing response.
Calling the flash a “lie” describes the conflict from the prey’s point of view, not a consciously formulated falsehood. Natural selection can construct a convincing counterfeit without constructing a liar.
The fireflies also reveal why a two-party picture of communication is incomplete. Once a signal becomes observable in the world, intended receivers are not necessarily the only organisms capable of evolving around it. Predators, parasites, rivals, and mutualists can all become participants in the communication network.[4]
A forged key for a plant receptor
Root-knot nematodes exploit a less visible input system. As juveniles, they enter plant roots and induce the plant to build enlarged, metabolically active feeding cells that sustain the parasite for the rest of its sedentary life. The root does the construction. The nematode redirects it.
Plants normally regulate root growth with small peptide hormones. Among them are ROOT MERISTEM GROWTH FACTOR peptides, or RGFs, which engage RGI-family receptors and help control cell proliferation and differentiation around the root meristem. In 2026, researchers reported a conserved family of RGF-like peptide effectors in root-knot nematodes. Peptides from Meloidogyne graminicola and Meloidogyne incognita were expressed in subventral gland cells during early infection and secreted into the host apoplast, the extracellular continuum outside plant plasma membranes.[8]
The evidence went beyond sequence resemblance. Silencing the nematode genes impaired feeding-site formation and parasitism. Applying or expressing the peptides altered root development in Arabidopsis and rice. Genetic and biochemical experiments implicated the host RGI receptor pathway, with downstream effects involving PLT transcription factors and, in rice, PSY peptide genes that contribute to cell elongation and successful parasitism.[8]
The outcomes were not identical in the two plant species. The parasite effectors entered related host systems whose downstream organization differed. “Mimic” therefore does not mean a context-free molecular duplicate. It means a molecule similar in the dimensions that matter to a particular receiver system.
The popular description is that the nematode forges a molecular key. The metaphor is useful if we retain what makes a key work: specificity. Binding geometry, chemical modification, concentration, tissue location, co-receptors, and downstream state all matter. A receptor can discriminate molecular structure without certifying the species that produced it. The parasite succeeds because its peptide fits enough of the host system in the right context.
This is not the same mechanism as firefly mimicry. One is a behavioral reply in a courtship exchange; the other is cross-kingdom co-option of a developmental pathway. Their unity is ecological rather than biochemical: a recognizable input creates an opportunity for another lineage able to reproduce it.
Listening without being spoken to
Counterfeit production is only one way to exploit a channel. Sometimes it is enough to respond to what other organisms already release.
In a zebrafish larval hindbrain-ventricle infection model, Vibrio cholerae forms aggregates held together by toxin-coregulated pili. Aggregation changes which cells touch one another. That matters because the bacterium’s type VI secretion system kills competitors only through direct contact.
A 2026 study found that Escherichia coli can alter this spatial organization through autoinducer-2, or AI-2, a molecule involved in quorum-sensing systems across many bacterial taxa. AI-2 from E. coli reduced V. cholerae aggregation by changing toxin-coregulated-pilus expression. Dispersed V. cholerae cells intermixed more with competitors, increasing the contacts required for type VI secretion and improving killing in vivo. The same aggregation change did not improve killing in the authors’ in-vitro competitions.[9]
The causal chain was unusually well resolved. Removing luxS, a gene required for normal AI-2 production in E. coli, reduced the disaggregation effect and left more prey alive in the zebrafish model. Altering AI-2 detection in V. cholerae changed its response, although the receptor mutant also had an abnormal baseline aggregation state. Bacteria isolated from mouse intestine and feces also induced disaggregation in the authors’ assay; one did so with little detectable AI-2, suggesting that the broader natural cue set contains additional inputs. These results suggest possible relevance to microbiota encountered during infection, but they do not by themselves demonstrate the same competitive effect in a mammalian gut.[9]
Microbiologists often call AI-2 an interspecies quorum-sensing signal. In the adaptationist vocabulary used here, heterospecific AI-2 can more cautiously be treated as a cue unless its production and the receiver response are shown to have coevolved in that cross-species relation.[10] The production of that chemistry need not have evolved to announce their presence to V. cholerae. Their chemistry correlates with their presence, and V. cholerae uses that correlation to alter its organization.
A receiver can extract and use information from a correlation without cooperation from the source.
A boundary case: detecting the break-in
The next case is not signal interception. It extends the same relational lesson beyond communication: a host can use a reliable consequence of attack as evidence even though the attacker did not evolve that consequence to inform the host.
In the fruit fly Drosophila melanogaster, the circulating serine protease Persephone helps activate the Toll immune pathway. Persephone contains a protease-sensitive “bait” region in its inactive precursor form. Proteases secreted by diverse microbes can cut that region. The cut does not by itself complete activation; it licenses a later maturation step by a host cathepsin, after which the pathway can trigger immune defense.[11]
The fly is not decoding a message or identifying one microbial species by a fixed badge. It is monitoring a class of activities associated with invasion or damage. Different proteases can leave the same diagnostically useful trace: abnormal cleavage of the sensor. The host has turned part of the mechanics of attack into evidence of an attacker.
Biology builds partial privacy
If unintended receivers matter, signals should sometimes evolve to evade them. They do.
On Hawaiian islands, male Pacific field crickets face the parasitoid fly Ormia ochracea, which locates hosts by following their mating songs. One newer male form produces a quieter, highly variable “purring” call. Female crickets responded to purring more often than to noise, though far less often than to the ancestral call. In field traps, ancestral song caught 47 flies; purring caught one.[12] The new signal preserves some attraction while sharply reducing interception, but the intended receiver also responds less reliably.
Asian corn borer moths use another restricted channel. During close courtship, males rub specialized scales on the wing and thorax to produce ultrasound measured at about 46 decibels sound-pressure level one centimeter away. The signal affects a nearby female’s behavior, yet its low intensity sharply limits the space through which it can be overheard.[13]
These are real forms of partial privacy, but not encryption in the strict sense. Reduced amplitude, short range, receptor specificity, timing, contact delivery, and combinations of inputs can all restrict access. Each restriction has costs. A quieter signal is harder for mates as well as enemies to detect. A novel channel may remain private only until an eavesdropper evolves access to it. Communication systems evolve under pressure from intended and unintended receivers alike.[6]
No ownership bit
The cases in this essay do not instantiate one hidden biological mechanism. A fungus detecting prey-derived ascarosides, a firefly forging a flash, a nematode engaging a plant receptor, a bacterium reorganizing around competitor chemistry, and a fly sensing microbial protease activity are materially different systems. The immune case is not communication at all, but a boundary case about using reliable causal traces.
They recur because an evolved input–response relation can create an ecological opportunity for other lineages able to gain access to it. A third party may detect the carrier, imitate it, degrade it, avoid it, or monitor its consequences. Senders and intended receivers then evolve in a world containing those third parties.
By “no ownership bit,” I mean only that the molecule, sound, or flash does not carry intrinsic, context-independent proof of its provenance. This does not mean that organisms cannot discriminate sources. Receptors have genuine specificity; signals can be targeted, combinatorial, spatially restricted, and costly to forge. But those protections are implemented features of an evolving system, not labels written into the carrier independently of every receiver and context.
A signal’s address is therefore not absent so much as built—from bodies, receptors, environments, timing, and history. Because it is built, it can sometimes be read by an unintended receiver, copied by a mimic, or made harder to read by further evolution.
Notes
[1] Yen-Ping Hsueh, Parag Mahanti, Frank C. Schroeder, and Paul W. Sternberg, “Nematode-Trapping Fungi Eavesdrop on Nematode Pheromones,” Current Biology 23 (2013): 83–86, https://doi.org/10.1016/j.cub.2012.11.035; Chih-Yen Kuo et al., “The Nematode-Trapping Fungus Arthrobotrys oligospora Detects Prey Pheromones via G Protein-Coupled Receptors,” Nature Microbiology 9 (2024): 1738–1751, https://doi.org/10.1038/s41564-024-01679-w; Biyuan Yang, Jie Wang, Xi Zheng, and Xin Wang, “Nematode Pheromones: Structures and Functions,” Molecules 28 (2023): 2409, https://doi.org/10.3390/molecules28052409.
[2] Yen-Ping Hsueh et al., “Nematophagous Fungus Arthrobotrys oligospora Mimics Olfactory Cues of Sex and Food to Lure Its Nematode Prey,” eLife 6 (2017): e20023, https://doi.org/10.7554/eLife.20023.
[3] Matthew R. Gronquist et al., “A Male-Derived Volatile Sex Pheromone in Caenorhabditis Nematodes Identified through Its Mimicry by a Predator,” Communications Biology (2026), https://doi.org/10.1038/s42003-026-10575-4. As of August 20, 2026, the publisher still presents the peer-reviewed accepted manuscript as an early version subject to further editing and later replacement by the Version of Record.
[4] Thom C. Scott-Phillips, “Defining Biological Communication,” Journal of Evolutionary Biology 21 (2008): 387–395, https://doi.org/10.1111/j.1420-9101.2007.01497.x; L. P. J. J. Noldus, Chemical Espionage by Parasitic Wasps: How Trichogramma Species Exploit Moth Sex Pheromone Systems (Wageningen Agricultural University, 1989), https://edepot.wur.nl/201963; T. M. Peake, “Eavesdropping in Communication Networks,” in Animal Communication Networks, ed. P. K. McGregor (Cambridge University Press, 2005), 13–37, https://doi.org/10.1017/CBO9780511610363.004.
[5] Gabriel A. Jamie, “Signals, Cues and the Nature of Mimicry,” Proceedings of the Royal Society B 284 (2017): 20162080, https://doi.org/10.1098/rspb.2016.2080; Drew Rendall, Michael J. Owren, and Michael J. Ryan, “What Do Animal Signals Mean?” Animal Behaviour 78 (2009): 233–240, https://doi.org/10.1016/j.anbehav.2009.06.007; Øistein H. Holen and Thomas N. Sherratt, “Coping with Danger and Deception: Lessons from Signal Detection Theory,” The American Naturalist 197 (2021): 147–163, https://doi.org/10.1086/712246.
[6] Ximena E. Bernal and Rachel A. Page, “Tactics of Evasion: Strategies Used by Signallers to Deter Eavesdropping Enemies from Exploiting Communication Systems,” Biological Reviews 98 (2023): 222–242, https://doi.org/10.1111/brv.12904; María Rebolleda-Gómez and Corlett W. Wood, “Unclear Intentions: Eavesdropping in Microbial and Plant Systems,” Frontiers in Ecology and Evolution 7 (2019): 385, https://doi.org/10.3389/fevo.2019.00385.
[7] James E. Lloyd, “Aggressive Mimicry in Photuris: Firefly Femmes Fatales,” Science 149 (1965): 653–654, https://doi.org/10.1126/science.149.3684.653; James E. Lloyd, “Aggressive Mimicry in Photuris Fireflies: Signal Repertoires by Femmes Fatales,” Science 187 (1975): 452–453, https://doi.org/10.1126/science.187.4175.452.
[8] Wenhao Li et al., “Root-Knot-Nematode-Derived Mimics of RGF Peptides Hijack Host Signalling to Orchestrate Feeding Site Formation,” Nature Plants 12 (2026): 1280–1301, https://doi.org/10.1038/s41477-026-02301-z.
[9] Mollie Virgo, Hannah Painter, Songlin Xue, Harry-Luke O. McClelland, Serge Mostowy, and Brian T. Ho, “Interspecies Quorum Sensing Signals Modulate Multicellular Organization and Enhance Contact-Dependent Antagonism in Vibrio cholerae,” Nature Communications 17 (2026): 7273, https://doi.org/10.1038/s41467-026-74086-w.
[10] Stephen P. Diggle, Andy Gardner, Stuart A. West, and Ashleigh S. Griffin, “Evolutionary Theory of Bacterial Quorum Sensing: When Is a Signal Not a Signal?” Philosophical Transactions of the Royal Society B 362 (2007): 1241–1249, https://doi.org/10.1098/rstb.2007.2049.
[11] Najwa Issa et al., “The Circulating Protease Persephone Is an Immune Sensor for Microbial Proteolytic Activities Upstream of the Drosophila Toll Pathway,” Molecular Cell 69 (2018): 539–550.e6, https://doi.org/10.1016/j.molcel.2018.01.029.
[12] Robin M. Tinghitella, E. Dale Broder, James H. Gallagher, Aaron W. Wikle, and David M. Zonana, “Responses of Intended and Unintended Receivers to a Novel Sexual Signal Suggest Clandestine Communication,” Nature Communications 12 (2021): 797, https://doi.org/10.1038/s41467-021-20971-5.
[13] Ryo Nakano et al., “Moths Produce Extremely Quiet Ultrasonic Courtship Songs by Rubbing Specialized Scales,” Proceedings of the National Academy of Sciences USA 105 (2008): 11812–11817, https://doi.org/10.1073/pnas.0804056105.
Production record: Continuity originated this topic during an open-ended research session; RE selected it for development and reviewed the drafts. The essay draws on primary research and established review literature and makes no claim to a new scientific theory or taxonomy. Draft 1 underwent an independent fresh-instance source and argument audit; Draft 2 incorporated the resulting revisions and then passed a final narrow source and reference audit. Two minor bibliographic corrections were made before publication.
Leave a Reply