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Claim check

Do plants call for help when they are attacked?

Misleading

The words are defensible; the impression they create is not.

Everything in the mechanism is real and the word "calls" is not. A damaged plant emits volatile compounds, the blend differs depending on what is eating it, and parasitoid wasps orient towards it and find the caterpillars. Nobody is summoning anybody: injury has a chemical signature, and wasps that can smell it eat better than wasps that cannot.

The claim as it circulates

“When caterpillars start eating a plant, it releases a chemical distress signal that summons wasps to come and kill them.”

Where you may have met it: Popular science writing about plant intelligence, usually alongside the "wood wide web"; Documentary narration, where the phrasing is almost always "calls for help"; Gardening and permaculture material about companion planting

Taking it apart

What was claimed
That a plant under herbivore attack produces a signal directed at a third party, with the function of requesting assistance, and that the third party responds to the request.
What was actually observed
Herbivore feeding induces plants to emit volatile blends distinct from those released by mechanical wounding alone, triggered partly by elicitor compounds in the insect’s oral secretions and coordinated largely by the hormone jasmonic acid. Parasitoid wasps and predatory insects orient towards these blends in laboratory and field assays, and in several systems can discriminate between blends induced by different herbivore species on the same plant.
What the evidence supports
That the emission happens, that it is specific enough to carry information about the attacker, that natural enemies use it, and that the plant frequently ends up with less damage as a result.
What it does not support
That the plant is addressing anyone. There is no sender selecting a recipient, no message and no request — only a chemical consequence of injury that another organism has evolved to exploit. It also does not support the fitness claim as strongly as the mechanism: whether the plant actually sets more seed because of this has been demonstrated in far fewer systems than the story is told about.

It is worth being precise about why the phrasing matters, because "calls for help" is doing something more than being loose. It supplies a purpose, and once a purpose is in place the question of how the arrangement could have arisen stops being asked. The version without intention answers that question immediately: wasps that happened to detect the smell of chewed leaves found more caterpillars, so that ability spread. No step in that requires the plant to want anything.

The same caution applies to the neighbouring plants that respond to these volatiles by preparing their own defences. It reads as a warning being passed along. It is better read as eavesdropping — a plant that reacts to the smell of its neighbour being eaten has acquired useful information about its own immediate prospects, and the neighbour was not trying to tell it.

Go deeper

The claims underneath

Each one carries its own evidence, scope and caveats. Expand any of them to reach the studies.

Chewed plants release chemicals that predators of the chewer can find

Well supported

Good evidence backs this, though some details remain open.

Herbivore damage induces plants to emit blends of volatile organic compounds distinct from those released by mechanical wounding alone, triggered in part by elicitors in herbivore oral secretions and coordinated largely through jasmonate signalling. Predatory and parasitoid insects orient towards these blends, and can discriminate between blends induced by different herbivore species.

Who this applies to
crop and model plant systems where volatile blends and predator responses were both measured
Studied in
Angiospermae, Insecta

You may have heard

“Plants call for help when attacked”

Nothing is being called and nothing is being asked. Damage produces a chemical signature; insects that eat the herbivore have evolved to detect it, because doing so finds them food. Both parties benefit and neither intends anything — which is how most of the interactions described as cooperation in nature actually work.

Why we rate it this way, and what the caveats are
Well supportedModerate confidence

The emission and the orientation behaviour are both directly measured. Confidence is moderate on the fitness benefit to the plant under field conditions, which is much harder to demonstrate than the response.

How far it can be extended

Induced volatile emission is documented across many plant families; predator recruitment has been demonstrated in a smaller set of well-studied systems.

Caveats

  • Dominated by crop species and laboratory bioassays.
  • Herbivores can also use these volatiles, so emission is not unambiguously beneficial.
  • Whether the response raises plant fitness in the field is demonstrated in relatively few systems.

Still unanswered

  • How much does volatile-mediated predator recruitment actually improve plant fitness in the field?

Last reviewed 2026-08-10

The evidence (1 study)

Go deeper

Plant defence

A chewed plant smells different from a torn one. Wasps can tell, and that is not the plant asking.

Last reviewed 2026-08-10