Firefly Larva

2021 January 10

Back on September 14, 2019, the girls found this delightful larva for me while shuffling around some dead leaves.


When it was feeling threatened it would stand still with its head hidden like that, but then it would shoot out its head a considerable distance and poke around with it.



Looking a bit closer at the head, we can see that it has a pair of mandibles that are long and pointed, and what looks like a proboscis that could maybe pierce into whatever the mandibles had hold of to suck out its juices. This looks like it would work well for soft-bodied prey like worms and grubs and maggots.


Looking at the side, the neck looks sort of like it has an elbow, so that the head could be pulled up underneath.


I’m pretty sure this is a firefly larva, probably one of the Pyractomena species. Their larvae look a lot like this. Other firefly larvae are broadly similar, but have different body shapes, different coloration, and not all of them can shoot their heads out like that. Although, they are all carnivorous.

When we flip it over, it had a pale stripe running down its belly, and the very last couple of segments look like they might have a light-generating organ.


A lot of the time, it kept the tip of its abdomen folded under.


We tried going into a dark room to see if it would emit light, but it didn’t cooperate. I’m told that normally firefly larvae will give off light (to the point where they are called “glow-worms”), but I guess they don’t do it all the time. Anyway, the theory about why the larvae would glow is as a warning that they taste bad. Since they normally live in the leaf litter or under rocks and logs, where there is no light, one can see how this would work. If they were just red or orange like a lot of other bad-tasting bugs, it won’t do any good, because they are in the dark and whatever might be after them can’t see anything. But if they glow, then the predator has something to see, and to learn to avoid. Of course, that only works for predators with enough intelligence to remember such things, like moles, voles, and mice. Not so good against, say, centipedes.

One Response
  1. January 29, 2021

    You know, it never occurred to me to wonder what fireflies ate or what they looked like as larvae. I guess I had figured that they got regular stipend checks from the other insects in exchange for being so charming, kind of like the supermodels of the insect world.

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