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Creature Feature #8 The amazing glowing scorpion!

Many times people spend several days visiting a rainforest like the one at Finca Bellavista Community and they are disappointed by how little wildlife they see. It can be that you just need to work on the art of seeing (and hearing). Diminutive granular poison frogs are much easier to locate once you learn their comb-like trilling. Forest birds give themselves away by their calls (although being up on the balcony of my treehouse, El Fenix, really helps you have a birds-eye view!). Most mammals, frogs, and numerous insects are nocturnal in habit, so you have to get your headlamp and venture out after dark to see them.

Then there are some that you might think are very uncommon until you start looking with a UV flashlight! Recently, platypuses were found to be bio-fluorescent, that is, their fur gives off a blue-green hue when illuminated by UV light. The same is true of several opossum species, flying squirrels, and numerous caterpillars. In the rainforest, scorpions may seem quite uncommon, until you power up your UV light. Even then, you need to know where to look. Trunks of trees, wooden steps, and rock walls are all good places to search for scorpions. You may be wondering why we want to see these dangerous creatures at all. Well, the species that occur in Costa Rica are not lethal to humans, and they are not very aggressive either. I remember once stripping my bed and finding a scorpion resting under the sheet. I was not stung, although I did carefully relocate the scorpion to outside my house. They can actually be quite helpful housemates as they hunt cockroaches and other pests, but I prefer them to stay in the kitchen.

Glowing scorpion
The same scorpion was photographed with and without UV light

So, why do scorpions glow? Nobody knows, but it is thought that glowing helps them detect UV – when they absorb UV they emit it and can detect these emissions with “photon-collectors” in their tails. Having an awareness of the surrounding UV may allow scorpions to avoid exposing themselves to predators. In the daytime they conceal themselves, but at night they are active and may be preyed upon by bats, owls and other animals. Being able to detect UV in their tails means they can be aware of light falling on their body even when the moonlight is too low for their eyes to register it. Well, that is the "official story" but I have my doubts. Whenever I have seen a scorpion and subjected it to a bright UV light, it never scuttles off to a darker spot. It remains motionless, intent on hunting. Perhaps they can use UV to detect one another, for territorial reasons or if searching for a mate?

It would be interesting to know what benefits other glowing creatures derive from UV. Caterpillars could well use it to conceal themselves from moonlight and hide from predators, but platypuses? The wonderful thing about nature is that the more you know, the more there is to discover!

by Fiona A. Reid

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