Bioluminescent Centipedes

I can’t believe I forgot to post this last year, but here is one of the coolest observations I had in Kenya.. credit for the find goes to my friend, Clayton Ziemke! Keep scrolling to find out more.

Just after the heavy rains at the mark of the wet season in central Kenya, walking around at night a faint green glow emanates from your footsteps. Almost invisible when painting your surroundings with a flashlight, when turned off the glow becomes bright and conspicuous, and even begins to writhe around smearing the glow around the leaf litter… It turns out this strange bioluminescence belongs to a soil centipede (Geophilomorpha), but not the body of centipede itself— a substance exuded from paired ventral organs on each body segment. I was shocked to observe this in a centipede because I had never heard of bioluminescence in centipedes, much less glowing of a substance and not the animal’s own body.

After digging in the literature, I was able to find a study in 1980 that describes luminous secretions in another species of littoral soil centipede (Orphnaeus brevilabiatus), found in the Indomalayan & Australiasian regions. The luminescent spectra showed two peaks at 480 and 510nm, the latter being the greatest intensity which likewise produced a green glow. The biochemistry of the reaction revealed enzyme-catalyzed oxidation of luciferin, a process found in many other bioluminescent animals such as fireflies, click beetles, and glowworms. The authors also note that the optimal pH for the reaction was unusually low (4.6 / more acidic) for a bioluminescent reaction.

So the substance may be acidic and distasteful, which is likely a predator deterrent, but why the glow? As for the function of the luminescent slime, there is nothing more than speculation. It could be that when being attacked by a terrestrial arthropod predator, the glow attracts attention from other nocturnal predators such as owls. Through the secondary predator’s intervention, the centipede may have a greater chance of escape. This is consistent with the fact that the slime is only exuded when contacted firmly and may only be advantageous when the centipede perceives its imminent demise. Similar hypotheses have been proposed for animals that shriek when captured, most famously the smoky jungle frog (Leptodactylus pentadactylus) in Costa Rica, in which the calls may attract crocodilians or cats. Alternatively, the glow could simply be a byproduct of evolving a distasteful secretion, neither detrimental nor advantageous during an encounter with a predator.

Photographed after unknowingly stepping on the centipede… observations do not always happen in a non-invasive way! To the left of the photo you can see the imprints of the centipede’s body smeared on the substrate, while the actual body extends all the way to the “S” on the right. In the middle there are a few elastic strands of slime.

Soil centipede (Geophilomorpha) illuminated by white light
Round-backed millipede (Spirobolida: Spirostreptidae); not a bioluminescent myriapod, but I thought I’d include it in this post! Photographed after capture [5]

A bicolored round-backed millipede grooms its thousands legs moving its mandibles all the way down to the posterior end. In Kenya, rainy and humid conditions spurred the emergence of millipedes. Among my favorites was this tubular and slick species in the order Spirobolida (family probably Spirostreptidae), a clade containing the largest millipedes on Earth. Most millipedes in the Spirobolida are easily distinguished by having a smooth, round body without ridges or crests. They are also well known for wrapping themselves into a flattened spiral when threatened.

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