The hole closes because its cells get bigger
A nematode enters a fungal ring. Three cells swell toward the opening and grip the animal. The loop does not tighten through a muscle pulling on it; the material around the hole expands into the available space.
The fungus is Drechslerella dactyloides, also studied under the older name Arthrobotrys dactyloides. Its branching filaments, called hyphae, can produce the ring. The trap is living fungal tissue, rather than a separate device assembled from debris.
The video’s cover illustrates the three-cell arrangement and inward movement. It is explanatory artwork, not a microscope image from the experiments. To understand the mechanism, separate three stages: growing an open ring, preparing it to inflate, and triggering the rapid change.
An open ring is not necessarily a ready ring
The 2023 Nature Communications study followed ring formation, maturation, and inflation with microscopy. It found a structure that could look complete before it could perform the trapping response. Nematodes could enter an immature ring and escape.
Under the study’s conditions, forming the ring took roughly four hours, followed by further maturation. Inflation then occurred in about 0.1–1 second. These are different timescales, not evidence that the whole trap grows in a fraction of a second.
A finished-looking ring can therefore be immature. If a worm passes through without being caught, the video alone cannot distinguish a trigger failure from incomplete preparation. The relevant follow-up is whether the cells had matured, including the membrane reserve described below.
Expansion has to be directed and survivable
A swelling cell faces two problems. Expansion in the wrong direction would do little to close the opening. Expansion that destroyed the cell would sacrifice the tissue doing the gripping.
The 2023 microscopy showed ring cells inflating inward, with changes to the cell walls. The outer wall ruptured while the inward-facing wall stretched. The plasma membrane and large internal vacuoles remained intact. Those observations help explain how dramatic shape change can occur while preserving the cell’s boundary.
A flexible membrane sits inside the supporting wall. It cannot simply stretch without limit. When the surface needs to become substantially larger, more membrane material must become available. This is a supply problem as well as a pressure problem.
“Like three inflating cushions” captures the geometry better than “like a tightening lasso.” But cushions do not explain cellular preparation. The fungus must have the necessary structures in place before a passing animal supplies the stimulus.
The membrane supply is prepared beforehand
The researchers found membrane-building vesicles accumulating and fusing near the inner side of maturing ring cells. They named the resulting structure the palisade-shaped membrane-building structure, or PMS.
After inflation, the PMS disappeared. Partly inflated cells had a wavy membrane, while fully inflated cells had a smoother one. Together with experiments disrupting membrane-related machinery, the observations support its role as a reserve for rapid membrane expansion.
The membrane reserve separates preparation from deployment: material accumulates during maturation, then becomes available during rapid inflation. The surface does not have to be manufactured from scratch in the fraction of a second when the trap closes.
The paper also investigated a membrane-fusion protein, DdSnc1. Disrupting it affected both the formation of the membrane reserve and inflation. The evidence therefore goes beyond spotting an interesting shape beside the membrane: interfering with part of the machinery changes the response.
This does not turn the entire trap into a solved engineering diagram. It explains an important constraint, how enough membrane can become available without tearing the cell open.
How does touch become a cellular response?
A cell can respond to mechanical force without a nervous system. Mechanosensitive proteins offer a route between a physical disturbance and changes inside the cell.
A 2026 mBio study investigated an MSL channel in nematode-trapping fungi. In D. dactyloides, deleting the relevant gene impaired normal ring behavior. The protein’s location changed during predatory development, becoming concentrated near the inner membrane and septal regions of ring cells.
The authors propose a connection between mechanical sensing, calcium-related signaling, and machinery involved in expansion. However, they could not directly characterize the channel’s electrical behavior. They also explicitly leave open whether the proposed pathway operates fast enough to explain sub-second inflation.
That boundary matters. Removing a component and observing a defect supports its importance. It does not reveal every step between the first contact and the final grip. The study identifies a promising mechanism while retaining a specific unresolved timing question.
The surrounding soil influences trap production
The fungus does not operate in an empty arena. A 2025 mSystems study used soil extracts and isolated bacteria to investigate rings growing directly from conidia, the fungus’s reproductive cells.
Bacteria including Acinetobacter and Pantoea stimulated those traps under the experimental conditions. Nutrients declined during incubation of the extracts, and the authors discussed competition and nutrient limitation as possible contributors. The exact mechanism by which individual bacteria induce the structures remained a subject for further research.
This is evidence about development in a particular experimental setting, not a recipe guaranteed to work in every soil. It makes the broader point concrete: the neighboring microbes and available nutrients can affect whether a predator establishes the structures it needs.
A microscopic capture is not a crop trial
Some nematodes damage plant roots, making predatory fungi interesting as possible biological controls. But trapping an individual worm answers a different question from consistently protecting a crop.
A sweetpotato study in BioControl tested fungal agents including A. dactyloides. The fungi reduced root-knot nematodes in laboratory soil microcosms. A separate ten-week glasshouse experiment found no significant difference in nematode populations in roots or soil between the fungal treatments and controls.
The result cautions against jumping from spectacular footage to a reliable agricultural treatment. Capture, establishment, and crop protection each require evidence at their own scale.
The ring’s speed is remarkable because so much happens before it moves. Growth creates the opening, maturation prepares the expanding boundary, and a stimulus initiates the grip. A few seconds of video reveal the final event; the experiments uncover the hours of cellular work that made it possible.
