2802: Fireflies

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I feel bad for Earth 2 and their shadowflies.
Title text: I feel bad for Earth 2 and their shadowflies.


Fireflies are varieties of beetles that emit flashes of light, a process known as bioluminescence. Megan explains that while this ability is not uncommon in ocean-dwelling species, it's pretty rare on land. Presumably, this is because sunlight doesn't penetrate very far under water, so there's evolutionary pressure there to develop a process to generate one's own light. Land animals, on the other hand, have much less need to generate their own light -- even at night there's light from the moon and stars, so nocturnal animals tend to have good eyesight or other enhanced sensory abilities (echolocation, olfaction, etc). It's thought that bioluminescence in fireflies originally served aposematically to ward off predators from larvae, but that it was co-opted as an adult mating signal. There are many varieties of bioluminescent fungus species, and the ecological benefit of that effect is uncertain. Some ocean-dwelling species, such as anglerfish, use their bioluminescence as lures for prey, whilst other creatures use it as camouflage. Yet others may employ such light as warning and/or as mating signals to deliberately reveal (not conceal) their presence. Often creatures with sufficient control of their phosphorescence can even fulfil multiple purposes according to need. These functions are similar to how organisms in more well-lit environments might normally rely upon surface hues (of skin, fur, feathers, scales, etc.) that work more (or less) passively under external illumination. Megan also mentions fatty acid enzymes, presumably a reference to luciferase, a class of enzymes used by fireflies and many other bioluminescent organisms.

While Megan and Cueball are walking towards a field with fireflies, she points all this out and suggests that it was just a fluke that fireflies developed this ability. When they see the firefly display, the two of them agree that we're lucky to be on a planet where this happened. Sadly, the moment may be fleeting as fireflies are going extinct, at least in North America.[1]

The title text suggests that there's an alternate Earth that has "shadowflies", which are presumably like fireflies but cast shadows instead of light, and that this isn't as nice for the people there. Since everything that's opaque casts a shadow[citation needed], this isn't really much of an ability. Possibly Randall's shadowflies have some sort of vantablack-like coating, or somehow create darkness near them beyond merely absorbing incident light (in violation of physics as we understand it). "Earth 2" is the name of an alternate world in the DC Comics universe, but it's unclear if this is the specific world being referred to. A presumably different alternate earth has been mentioned before. Earth 2 may also be a reference to an actual exoplanet which appears very similar to Earth.


[Cueball and Megan are seen in silhouette (drawn in white against a black background) throughout the strip. They are walking to the right.]
Cueball: So where is this spot?
Megan: It's just up ahead.
[Cueball and Megan continue walking.]
Megan: You know,
Megan: fireflies didn't have to exist.
[Closeup on Megan.]
Megan: The ocean has lots of bioluminescence, but it's less common on land.
Megan: Creatures that glow are pretty rare here.
[Cueball and Megan continue walking. The light of one firefly is seen to their right.]
Megan: So it's not some niche whose exploitation was inevitable.
Megan: If insects hadn't stumbled on their fatty acid enzyme trick, Earth just wouldn't have fireflies.
Megan: Ooh, look!
Megan: They're starting!
[A panel as wide as the first four combined and below them. Cueball and Megan stand in the tall grass, at night, and many stars can be seen in the sky above them. Above and below them, to their left and right, the lights of dozens of fireflies can be seen.]
Cueball: I'm glad we got a planet that has these.
Megan: Yeah, it's a good one.

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I can't remember another XKCD which has gray-scale figures. -- Dtgriscom (talk) 01:46, 15 July 2023 (UTC)

I think 2386: Ten Years also had gray-scale figures, but just for one panel. --nixstyx (talk) 02:37, 15 July 2023 (UTC)
Yup: https://xkcd.com/2386/

https://www.usatoday.com/story/news/nation/2022/07/02/fireflies-possible-extinction-across-us/7795410001/ very sad. 02:20, 15 July 2023 (UTC)

another suggestion for “shadow flies”: in certain interpretations of quantum physics entities in other possible worlds are referred to as “shadow ___” (e.g. “shadow photons”). 04:23, 15 July 2023 (UTC)

I expect a visitor flood to [2]. ~ Megan she/her talk/contribs 07:24, 15 July 2023 (UTC)

When I saw this, especially the last panel which is reminiscent of the night sky scene in https://xkcd.com/2386/, I thought it was Randall and his wife.  So how and when do we know when we are seeing Cueball and Megan and not Randall and Mrs. Randall?  Or are Megan and Cueball their in-universe stand-ins? RAGBRAIvet (talk) 00:01, 16 July 2023 (UTC)

Wow. I can't remember the last time Randall shared a "romance" comic. Shamino (talk) 23:42, 16 July 2023 (UTC)

Maybe Earth 2 doesn't really have any darkness, in which case their shadowflies might be equally enchanting to them as fireflies are to us. 08:27, 17 July 2023 (UTC)


I’d love to understand what’s going on with the “starving” comment. Are fireflies starving themselves to get that enzyme to work? Ptdecker (talk) 08:04, 15 July 2023 (UTC)

I can't currently see "starving" anywhere. (Old edit?) Unless you misread "They're starting"..?

What's the "fatty acid enzyme trick" that Megan mentions? --NeatNit (talk) 11:46, 15 July 2023 (UTC)


Fireflies are disappearing on our planet. So one read I'm having of this comic is the ecological impact we, humans are having on the planet and other species.

~ dmathieu


In The Best of the Journal of Irreproducible Results (page 180) there's an article "Definition of a Darkbulb" by James L. DeLucas, which would be relevant to the idea that "shadowflies" might generate darkness in their surroundings beyond merely absorbing incident light. But I can't find a linkable copy of the article. BunsenH (talk) 15:55, 16 July 2023 (UTC)

ProphetZarquon (talk) 16:51, 16 July 2023 (UTC)
I did find that one. But it's a poor reproduction of the original, with ADDED CAPITALIZATIONS of words that aren't even emphasized in the original, and lacking the accompanying illustrations. And the ".asc" filetype isn't ideal either; in these decadent days, it's not recognized as an (ASCII) text file by my Windows box. BunsenH (talk) 02:13, 17 July 2023 (UTC)

wow this came out the Day I saw fireflies in a long while GetPunnedOn (talk) 22:57, 17 July 2023 (UTC)

Earth 2

I remember there was a TV series by the name Earth 2 (https://en.wikipedia.org/wiki/Earth_2_(TV_series) ), not sure if this is of relevance here but I immediately thought of it when I read the title text. It's too long for me to remember if there where any shadowflies occurring, but perhaps somebody has better knowledge than I do


Ah, so Earth 2's infested by the Vashta Nerada? That would certainly constitute grounds for feeling sorry for them. Whoop whoop pull up (talk) 11:18, 10 November 2023 (UTC)