Illumination: The beetle sheds bright light in a 10-foot radius and dim light for an additional 10 feet.

A giant fire beetle is a nocturnal creature that takes its name from a pair of glowing glands that give off light. Miners and adventurers prize these creatures, for a giant fire beetle's glands continue to shed light for ld6 days after the beetle dies. Giant fire beetles are most commonly found underground and in dark forests.

It's not clear from this feature or description if the beetle shines this light 24/7, or has the ability to dim itself. Has this creature been in previous versions of D&D? Is it based on a real-life counterpart?


The answer to questions like this always ends up depending entirely on your playstyle.


The gamist answer to this question is "no." The game rules are all that create the abilities and their operation, and the rules don't say it can be suppressed. You would choose the gamist answer if you desire a rules-first/RAW playstyle where the rules determine the physics of your game world.


The simulationist answer to this question is probably "yes." Real world fire beetles can control the degree of their luminosity, so it'd be a reasonable extension that giant ones do too. You would choose the simulationist answer if you focus more on the fictional game world and consider the rules to be a simplified abstraction of this that you can augment with "reality" as needed.


The narrativist answer to this question is "maybe." You'd decide either based on what is more interesting to the plot, or based on the fact that an interested PC is asking is an opportunity to let them answer the question themselves as part of sharing the narrative responsibility for the game. You would choose this if you are more focused on the plot of the game and are comfortable with it not flowing directly from the rules or being consistent with other campaigns.


All of these are valid playstyles with their own pros and cons outside the scope of this question, but the point is that there is no "right" answer to this question, it depends on your perspective on the game, and there is no "right" perspective. Understand your own perspective and needs, and then the answer that fits that perspective follows.

Earlier editions of D&D and the general D&D play community has leaned in specific directions on these playstyles over time, for example in 1e-2e time there were plenty of "Ecology of the Fire Beetle" type articles written from a sim point of view, while 4e was very strictly gamist with a slight amount of narrativism, but with 5e it's been left deliberately agnostic so you can use whichever style you and your players prefer fairly readily.



In the description you posted, it says "the beetle sheds bright light in a 10-foot radius and dim light for an additional 10 feet."

This is an absolute statement like racial traits such as darkvision. The beetle sheds bright light, and has no say in the matter. Similarly, elves have darkvision absolutely and cannot turn it off.


As of RAW, no, the beetle can't change the emitted light level.

The Flameskull (MM 134) also has the illumination trait, but with an additional feature:

Illumination. The flameskull sheds either dim light in a 15-foot radius, or bright light in a 15-foot radius and dim light for an additional15 feet. It can switch between the options as an action.

The beetle does not have this in its trait description, which induces it is not able to change the emitted light level like the Flameskull could.

If you need an on/off switch for the beetle, here are some additional thoughts.

Some real insects, like the common glow-worm, are able to control that:

The insect can regulate its light production by controlling the oxygen supply to the light emitting membranes containing luciferin. (Wikipedia).

The fact that the glands of the Giant Fire Beetle stop emitting light after 1d6 days suggests that there is probably a chemical reaction that simply stops after a while, and this could be because the glands run out of oxygen. So, the beetle could have some influence on the emitted light level.

(Note: the confusing part about the Giant Fire Beetle though, is that this trait does not seem to be of any use for it, as it has blindsight 30 ft.)

  • \$\begingroup\$ Note: real world fire beetles use bioluminescence to attract prey and for the sexing, not to see with. \$\endgroup\$
    – mxyzplk
    Feb 19 '16 at 23:09

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