Does a firefly glow only when adult or larva? Or does it glow during its whole life. By glowing, I mean that they glow only when they require, not all the time.

Is there a reason (evolutionary reasoning) why they glow? Also, if the answer is all the time, then why, or if the answer is specific period in life then why?

  • $\begingroup$ Is this a homework question? And why would they be required to glow? And what does the last sentence mean? $\endgroup$
    – AliceD
    Mar 31, 2017 at 6:35
  • $\begingroup$ @AliceD It is not a homework question. Is there a reason (evolutionary reasoning) why they glow? Last sentence means that if the answer is all the time, then why, or if the answer is specific period in life then why? $\endgroup$
    – YAHB
    Mar 31, 2017 at 6:41
  • $\begingroup$ Gotcha. The way the question is posed it just tastes like homework. In fact, two of the close votes are based on homework suspicion. I would edit the question to remove the demanding undertone and improve its clarity. $\endgroup$
    – AliceD
    Mar 31, 2017 at 6:43
  • $\begingroup$ A reason is a reason. Keep it simple. Ask whether it performs a function and keep evolution out of it unless your question is specifically about evolution (which it isn't). $\endgroup$
    – David
    Mar 31, 2017 at 14:20
  • $\begingroup$ @David I think AliceD suggested corrections the way that the meaning of my question won't change. It is clear enough. Maybe you should make the edits. (If you feel so.) :) $\endgroup$
    – YAHB
    Mar 31, 2017 at 14:53

1 Answer 1


Fireflies 'glow' in larval and adult stages but for very different reasons. It is thought that glowing behaviour first evolved in larvae to deter predators(Branham and Wenzel (2003)). This is an example of an aposematic warning, which uses bright colours, smells, sounds, or in this case light, to tell predators they are undesirable as prey. Sometimes a prey animal will use an aposematic warning to tell predators they are poisonous, or simply to mimic a prey that is poisonous. In the case of firefly larvae, they don't taste good to predators because of a steroid compound in their bodies (Branham (2005)).

Adults also glow, but do so in a synchronized pattern of flashes to communicate with mates (Carlson and Copeland (1985)). Mates will time their flashing with physiological fluctuations and even respond directly to another individual's flashing pattern with appropriate delays and timing of responses.

So to answer your first question, fireflies are not continuously glowing, but flash at night as larvae to deter predators, and during active mating as adults.

Your second question can get into a long-winded explanation of how certain traits evolve in response to a pressure, but to simplify, it's likely that fireflies evolved glowing because it relieved predation pressure. This ability then evolved further to communicate the quality of mates more efficiently than phermone signalling.


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