Hunting for scorpions
Seeking one of Earth’s most ancient land invertebrates.
It is true that all scorpions sting, and that all are venomous. It is true that they hide in places where they’re hard to detect, and then ambush their prey — or your foot — in a vicious attack. And, yes, they brutally crush their victims in their pincers, stinging their prey with a paralyzing toxic soup of neurotoxins and enzyme inhibitors before subjecting it to a tissue-dissolving acid spray, after which they coolly slurp up whatever’s left.
On the other hand, they are among the planet’s oldest invertebrates, and they have the substantially redeeming quality of glowing under ultraviolet light.
There has been considerable debate about scorpion luminescence, but the most persuasive explanation is also the most astounding. Although scorpions are well-endowed with eyes –– one pair on top of their cephalothorax (“head-chest”) and another two to five pairs along the front sides of it –– they have lousy eyesight outside the blue-green spectrum. That’s unfortunate, considering that the main hazard of scorpionhood is being spotted in the moonlight by a predatory lizard, snake, rodent or bird, and getting picked off. The best way to avoid this fate is to take cover, but how can the scorpion know whether it is in danger if its eyes are unable to detect the wavelength of light emanating from the moon? Their elegant solution, it appears, has been to evolve a cuticle that is charged with beta-carboline and other luminescent chemicals. When the scorpion’s exoskeleton is struck by moonlight — which, as a reflection of sunlight, contains some of the same UV rays — it glows. In this sense, the scorpion’s entire body functions as an eye, one that is highly sensitive to small amounts of UV light. If a scorpion sees itself luminescing — something it can do only because the wavelength of its luminescence falls within the blue-green spectrum — it knows that it is exposed and must seek cover. Somewhere deep within its 450-million-year-old nogginchest,- the scorpion says to itself: “Dang, my ass is glowing again. Better head for the sagebrush!”
Scorpions’ fabulous luminescence also allows desert- rats like me to traipse around on moonless nights, UV flashlight in hand, searching for them. One night, my buddy, Steve, and I set out just after dusk, knowing that we had only 90 minutes before the rising of the full moon, which would flood the desert with light, set scorpion butts aglow, and send their owners scuttling into hiding. It was a breezy night, which is not ideal for a scorpion search. Scorpions stalk insects by detecting vibrations through sensory organs in the tips of their legs and specialized hairs on their pincers, so wind can disturb their hunting strategy and keep them tucked in their burrows. But we soon discovered scorpions near juniper snags, around sage and bitterbrush, in rice grass, even out on sandy flats between patches of mule’s ears. The scorpions glowed beautifully in otherworldly splashes of bright purple beneath our lights as they tunneled through the darkness.
I am only slightly ashamed to admit that the high point of the evening was encountering a torrid bout of scorpion sex. Steve and I witnessed two scorpions doing what arachnophiles call the promenade à deux, an appropriately French term for the creature’s elaborate, highly ritualized mating “dance.” The male grasps the female’s pedipalps (little mouth claws) in his, and then dances her around looking for a good place to deposit his spermatophore, the sperm packet that she will take into her genital operculum, thus triggering release of the sperm. This courtship dance can also involve “juddering,” in which the scorpions shudder and convulse, and the “cheliceral kiss,” during which the male uses his pincers to hold the female’s pincers in a gesture that looks to me like holding hands.
I have neighbors who say that in years of living out here in the remote high desert they have never seen a scorpion. In 90 minutes of night hiking, Steve and I saw 80 scorpions, each of them glowing with 450 million years of evolutionary good fortune. I find it fascinating that in all this wide, wild, windy desert, nothing glows under UV light but the scorpion. What if we had a flashlight that illuminated only spiders, or snakes, or rodents? What if we could match the stunning diversity of life here with an equally rich mode of perception?
Those who dismiss this Great Basin landscape as “empty” are looking at something that they are unable to see. This desert is emitting its spectacular beauty in a wavelength their eyes have not yet evolved to detect. To call this place barren is simply to admit an inattentiveness that is the perceptual equivalent of blindness.
When I told one of my neighbors about last night’s scorpion safari, he asked, “Where in the world do you find scorpions out here?” I paused before replying. “Everywhere.”
Michael Branch writes Rants from the Hill, a monthly essay series available at hcn.org. He rants from a remote hilltop in the Great Basin Desert of western Nevada.
