Scorpions or scorpions are a very ancient order of arachnid arthropods, in fact, they have been on Earth for about 435 million years . Some of the ancestors of modern scorpions could measure up to 1.2 meters. They currently have almost 2000 living species , of which new discoveries are still being added.
They are true survivors, capable of living in virtually any area with a tropical or temperate climate, from extreme deserts to rainforests. Its eight legs, capable of keeping them hanging upside down; its two grasping claws , to catch its prey; together with a poisonous stinger , to immobilize them without problem, they turn them into true superheroes.
But without a doubt, the most striking power of most scorpions is their ability to glow with a blue-green color under ultraviolet (UV) light , that is, they are fluorescent. This fact was discovered independently by the zoologists RF Lawrence and M. Pavan, in 1954. Something that meant a paradigm shift in the study of these animals, since from then on it was much easier to locate them at night with black light lamps. .
But, what is the reason for such capacity? It turns out that, only in adult specimens, as the hardness of their cuticle increases, a kind of protective layer, two fluorescent compounds are secreted and accumulated in the exoskeleton: the chemicals β-carboline and 7-hydroxy-4-methylcoumarin , which glow under UV light even after the scorpion dies.
Now we know what makes them so bright in the light of the full moon. However, what is the use of being fluorescent? What adaptive benefits does this trait bring them apart from being the coolest when sneaking into clubs? Well, it turns out that, unfortunately, very few studies have tried to find out its ecological role. However, there are different theories on the table:
- Ultraviolet light detection and communication between scorpions. According to a study from the University of Oklahoma published in Animal Behavior , some of the eyes of scorpions could reach their maximum sensitivity in green light (500 nm) and secondly in UV light (350 – 400 nm). By being able to see each other at night, some form of visual communication could take place, either for courtship or to avoid conflict.
- Avoid predators . Some scientists speak of an aposematic function, that is, a warning of its dangerousness to its predators to avoid being eaten.
- Attraction of prey. A team from the University of Panama published a study on this in the journal Neotropical Biodiversity , using crickets as potential prey. Unfortunately, there were no significant differences between the number of hunts of fluorescent and non-fluorescent scorpions.
Despite the hypotheses, the fluorescence of scorpions remains a mystery to science . It could also be that the formation of these compounds had no ecological function.
References:
Gaffin, D. D., Bumm, L. A., Taylor, M. S., Popokina, N. V., & Mann, S. (2012b). Scorpion fluorescence and reaction to light. Animal Behaviour, 83(2), 429–436. https://doi.org/10.1016/j.anbehav.2011.11.014
Gálvez, D., Nieto, C., & Samaniego, P. (2020). Test of the prey-attraction hypothesis for the scorpion fluorescence. Neotropical Biodiversity, 6(1), 172–177. https://doi.org/10.1080/23766808.2020.1844991
