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Insectsspecies group

Fireflies

Lampyridae

A firefly flash is a code — so it can be forged. Some females answer another species’ code, eat the males that reply, and keep their chemical defences.

A firefly flash is a species-specific code — a pattern of timing that identifies who is signalling. Which is why it can be forged: Photuris females answer the code of another genus, eat the males that come, and take their chemical defences.

The flashing is a conversation with a grammar. In many North American species a flying male produces a species-specific pattern — so many flashes, of such a duration, at such an interval — and a female of his species, perched, answers after a characteristic delay. The identifying information is in the timing rather than the brightness, which means the system is a code, and a code is something that can be reproduced by someone who is not entitled to use it. That is exactly what happens. Females of the genus Photuris answer the flash patterns of Photinus males, matching the response of a Photinus female closely enough to draw the male in, and then eat him. This was demonstrated in the field in the 1960s using nothing more elaborate than a penlight: an observer can produce a given species’ pattern on demand and watch which females reply. It is one of the cleanest examples of aggressive mimicry known, and unusual in that the mimicked signal is temporal rather than visual resemblance. The reason it matters beyond being remarkable emerged thirty years later. Photinus fireflies carry defensive steroids that make them unpalatable; Photuris do not make these compounds. Females that have eaten Photinus have them, and are rejected by jumping spiders that eat females which have not. So the hunting is not only about food — it is how these females acquire a chemical defence, by the same sequestration route poison frogs use for their alkaloids. The popular framing of all this is heavily anthropomorphic, and NatureHQ does not use it. What has been demonstrated is that these females reproduce another species’ signal, capture the responders, and thereby obtain a defence. Nothing in that requires any claim about what the animal knows or intends.

Early coverage · 31% complete · reviewed 2026-09-03

What this page covers

Over two thousand beetle species worldwide. Not all of them flash — some glow steadily, some are active by day and use scent instead, and in several species only the larvae produce light.

Often confused with: Flies, which fireflies are not — they are beetles; Glow-worms, which in Britain are the flightless females of a firefly and elsewhere may be fungus gnat larvae; All fireflies flashing to attract mates, when several do not flash at all

Quick facts

The signal is timing
Species are identified by flash pattern and response delay, not brightness
Codes can be forged
Photuris females answer Photinus patterns and eat the males that reply
And it is not only a meal
They acquire defensive steroids they cannot make themselves
Not all fireflies flash
Some glow steadily, some are diurnal and use scent instead

The flash is a code, not a light

The identifying information is in the timing.

Photuris females reproduce the answering flash of another firefly genus, draw in the males that reply, and eat them — and by doing so acquire a chemical defence they cannot manufacture themselves.

Well supported

Good evidence backs this, though some details remain open.

Female Photuris fireflies emit response flashes matching the species-specific patterns of Photinus females, attracting Photinus males which they then capture and consume. Photuris lack lucibufagin steroids endogenously and acquire them from consumed Photinus, gaining measurable protection from predators.

Who this applies to
Demonstrated in Photuris females preying on Photinus; behaviour varies across the many Photuris species.
Studied in
Photuris, Photinus
Why we rate it this way, and what the caveats are
Well supportedHigh confidence

The mimicry was demonstrated experimentally with reproduced flash patterns, and the chemical acquisition was measured directly before and after feeding, with a predator assay confirming the protective effect.

Caveats

  • Photuris contains many species and their behaviour is not uniform; this is not a description of all fireflies or even all Photuris.
  • The protective benefit was assessed against jumping spiders, so it is demonstrated against that predator specifically.
  • The popular framing of this behaviour is heavily anthropomorphic and imports intent that no experiment has tested.

Still unanswered

  • How a female matches the correct answering pattern for whichever species is signalling, which is a discrimination problem nobody has resolved.

Last reviewed 2026-09-03

The evidence (3 studies)

How we know

Answering a firefly with a penlight

Female Photuris fireflies are seen eating males of other species. Are they attracting them by reproducing their mating signals?

Field observation of Photuris females responding to signalling males of other genera, combined with experimental playback: the observer used a penlight to reproduce species-specific flash patterns and recorded which animals responded, with what pattern, and what followed.

What happened

Photuris females answered Photinus male flash patterns with the response pattern of a Photinus female, drew the males within reach, and captured and ate them. Females adjusted their answering pattern to the species signalling.

What it shows

Aggressive mimicry using a temporal code rather than an appearance — one species reproducing another’s mating signal to obtain prey. The penlight makes it a manipulation rather than an observation: the experimenter can produce any species’ pattern on demand and see who replies.

What it does not show

Field work at night, where attributing behaviour to identified individuals is difficult. Photuris contains many species whose behaviour differs, so this is not a description of the genus. It also says nothing about how a female recognises which code she is hearing or selects the matching reply.

The controls — what makes this evidence rather than a story
  • Flash patterns reproduced by the observer, so the stimulus is controlled and can be repeated at will rather than waited for.
  • Different species’ patterns presented, testing whether responses are specific to the code rather than to any light.
  • Responses recorded alongside the outcome, linking the signal to the capture rather than to proximity alone.

From Aggressive mimicry in Photuris: firefly femmes fatales

The penlight is what makes this experimental rather than anecdotal. An observer holding a torch can produce any species’ pattern at will, in the field, and see which animals answer — which turns a claim about signal codes into something you can manipulate and test. Very few communication systems in nature can be entered by a human being with a household object.

Diagram

The signal is timing, so it can be forged

The identifying information is in the pattern, not the brightness.

The signal is timing, so it can be forgedPhotinus malea species-specific patternPhotinus femaleanswers after a set delayPhoturis femalethe same answer — and she eats himAnd she keeps his defensive chemicals, which she cannot make herself.
The same explanation in words

Three timelines. On the first, a Photinus male emits a species-specific pattern of flashes at set intervals. On the second, a Photinus female answers with a single flash after a characteristic delay. On the third, a Photuris female produces the same answering flash at the same delay — and eats the male that approaches. Because the species identity is carried by timing rather than by appearance, the signal is a code, and a code can be reproduced by something not entitled to use it. The female also keeps the defensive chemicals from the male, which she cannot manufacture herself.

The part that is not about food

The prey carry a chemical defence the predator cannot make.

Photinus fireflies contain lucibufagins, steroids that make them unpalatable. Photuris females do not produce them — and females that have fed on Photinus do contain them, and are rejected by jumping spiders that readily eat females which have not. So the mimicry, the predation and the chemical defence are one system: a signal is forged to obtain prey, and the prey supplies protection.

This is the same route poison frogs use. An animal that cannot manufacture a defence obtains it by eating something that can — which makes the defence a property of what is available to eat rather than of the species.

Where this connects

A note on how this is usually described

The standard phrasing imports a mind nobody has tested for.

This behaviour is almost always written up in the language of seduction and betrayal, and the phrasing does real work: it makes the female sound like a deceiver executing a plan. What has actually been demonstrated is that she produces a response pattern matching another species’ signal, that males of that species approach, and that she captures and eats them, thereby acquiring a defensive chemical. Every part of that is remarkable. None of it requires her to know what she is doing.

  • How does a female produce the right answer for whichever species is signalling?

    Why it matters: A Photuris female may answer several different species’ patterns, each with its own timing. Doing that requires recognising which code is being sent and selecting the matching reply — a discrimination problem that has not been explained, and one of the more interesting unanswered questions in insect behaviour.

    What would settle it: Controlled playback of interleaved species patterns to individual females, measuring which replies they produce and how quickly they switch.

The research behind this page

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

1997Proceedings of the National Academy of Sciences

Firefly “femmes fatales” acquire defensive steroids (lucibufagins) from their firefly prey

Photuris females lack the defensive steroids that Photinus fireflies carry, and acquire them by eating Photinus.

1994Journal of Chemical Ecology

Dietary source for skin alkaloids of poison frogs (Dendrobatidae)

Frogs raised without their natural prey lacked skin alkaloids almost entirely.

1965Science

Aggressive mimicry in Photuris: firefly femmes fatales

Photuris females answered the flash codes of Photinus males with the response pattern of a Photinus female, drawing the males close, and then captured and ate them.

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 31% completeness against what we would call a finished subject, and was last reviewed on 2026-09-03. It carries 1 claims and answers 0 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
  • The flash-code work is from North American species; firefly signalling elsewhere, including synchronous flashing in Asia, is not covered.
  • Larval bioluminescence, which is widespread and probably aposematic, is mentioned rather than treated.
  • How a female selects the correct reply pattern is unresolved.