A scorpion, according to most, is a symbol of cruelty; tangible evidence that nature has a mean streak. However, as with all fauna, when we turn an attentive eye to the creature we will see something worth observing. A scorpion is more than pincers and a stinger. It too needs to make its way in the world, wary of predators and ultimately reproducing to be considered successful. When we start to understand this feared animal as a piece of our biome, a necessary strand in the food web, and appreciate it in its own right, our anxiety will diminish, our fears soften, and perhaps, our curiosity heighten.
Living with Humans
Here in southwest Arizona it is common to encounter three species of scorpions: bark, stripe-tailed, and giant hairy. These types are widely distributed and many people have had an intimate experience with the bark scorpion (Centruoides sp.). However, in the desert it’s important for humans to learn to live in harmony with their neighborhood plants and animals. Like you, scorpions are attracted to cool dry places. Typically, they hide in small crevices, under boxes, and in corners of garages. To prevent entry into your home, make sure that all windows and door frames are sealed tightly and that dusty forgotten places are swept regularly. These techniques will help discourage residency by our eight-legged friends.
If you’d like to see them, summer is the best time to search for active individuals. Buy a black-light flashlight and go out at night. A scorpion’s chitinous exoskeleton fluoresces under UV light, so it is easy to see them glowing in a rock wall after dusk. Use this technique to search your house for unwanted visitors. Gently sweep them into a cup or container with a piece of paper, cover the cup, and release them outside. Maintain this chore regularly to avoid surprises!
Scorpions comprise one order in class Arachnida with approximately 1,900 representatives. They are some of our oldest terrestrial animals, evolving from an ancient crab that came ashore, toweled off, and adopted an attitude over 400 million years ago in the Silurian period. Rest assured our modern scorpions would be easy to overlook compared to the ancient meter long (about 3 feet!) fossilized individuals that are ensconced in rock.
As an arthropod, scorpions are most closely related to tailless whipscorpions and vinegaroons and more distantly to spiders, mites, and crustaceans. All arthropods have jointed appendages, bilateral symmetry, and that crunch factor: an exoskeleton. Scorpions are defined as a unique group within this phylum by their well- developed claws (pedipalps), and stinging tail (telson). However, these distinct characteristics also make them a model of nomenclature for other arthropods with intimidating forelegs or a piercing appendage including sea scorpions, scorpion flies, water scorpions, microwhip scorpions, pseudoscorpions, and wind scorpions.
To study a scorpion, one’s eye is drawn to two apparatuses at polar ends of the animal. The first feature is their pedipalps. These are well developed pincers, a smaller yet strikingly similar version of king crab claws, toothy edges and all. The size of the pedipalps in relation to body size is not consistent within scorpions. Some, like the emperor scorpion (Pandinus imperator) intimidates with incredibly large bulbous pincers, while a small bark scorpion (Centruoides sp.) has relatively slender elongated pincers.
As a general rule there is an inverse relationship in that the larger the scorpion (and its pincers) the less dangerous it is. The smaller the pincers, the more toxic its venom. If an animal looks scary, it doesn’t have to be scary. Conversely, a small inconspicuous scorpion needs a way to quickly intimidate and retaliate if it’s disturbed. Not just for show, the pincers are utilized in many ways. When stretched out they help to make the animal look big and fierce, they are used for seizing prey in a vice grip, for dragging mates around in a dance, or holding food to their chelicerae, much like a person holding a sub sandwich to his or her masticating jaw.
Traveling down the body of the scorpion from the pincers we first encounter the head, or cephalothorax, then the abdomen which houses most of the necessary internal organs. On the underside of the scorpion, near the front of the first of its four pairs of legs are some curious adornments- the pectines. These are two hairy fan-like structures which aide in sensory location by helping feel substrate vibrations or even picking up on smells. Flipping back to the dorsal side, we see the visible ecdysial lines, the very apparent segmentation of the abdomen.
This leads to the tail portion- the second of its defining appendages making the scorpion look as though someone drew a curlicue on the end of a bug. Five styliform segments lead to the stinger, the staccato ending of our creature. The thin barb administers venom more accurately and certainly more suddenly than any hypodermic needle. The tail is held up and over the abdomen ready for employment. Warning signs of death appear here as well. Dark lines or spots on the tail forecast the scorpion’s eminent demise. Finally, a flat tail is a bad tail- signifying a dead arachnid.
Engaging all its various adaptations, the scorpion lives a successful yet lonely life, mostly in arid regions of the world. The solitary individual is a predator, and keeps in check populations of other arthropods such as crickets, grasshoppers, beetles, and other scorpions. Scorpions produce no silk and have no architectural means of entrapment so when an insect thoughtlessly approaches, the scorpion grabs lightning quick with its pedipalps and paralyzes rapidly with its venom. All the while it must avoid becoming prey to centipedes, spiders, ants, frogs, lizards, birds, mammals, or other scorpions. To escape heat and predation the scorpion tends to be nocturnal. Most of the time these are secluded creatures- they eat when they can, leaving cricket carcasses strewn about their habitat, whiling away the time in darkness much like a bachelor who has never left the basement.
When an attempt to be social is made it’s for copulatory purposes. The joining of gametes is every animal’s evolutionary drive so the scorpion must brave the rough ecosystem in order to carry on the species. While out hunting- for prey or mate- they are not agile delicate creatures. One can envision them gliding across the substrate like a silky stingray but this is not the case at all! Their arms are stretched to cover as much area as possible, the eyes so dorsally located as to not see the ground, and they make jerky skittering movements much like a large construction vehicle navigating a rocky terrain. To make this treacherous awkward trip, there better be a reward.
A lucky male, upon encountering a female cannot just get to the business of reproduction right away. He must be romantic and woo his intended mate. Facing the female, the smaller male will do a dance called a promenade à deux for up to an hour! If that held her attention, he then unceremoniously deposits a sperm packet on the ground, grasps the female with his pincers, and drags her over his gift. The definition of arachnid romance. The female then absorbs the packet into her body, and hopes for release as the male has probably been stinging her thus while. It is not at all uncommon for the female to try to eat the male at this point, exemplifying Shakespeare’s quote that “journeys end in lovers’ meeting.”
After the promenade, the female does get to employ some choice. She can either use the sperm immediately or save it for up to a year (if she doesn’t molt) waiting until motherhood becomes convenient. There are no eggs laid; rather, the mother gives birth to live young. Depending on species, anywhere from a few to several dozen of the babies exit her, climb up her legs, onto her abdomen where they will reside for one to three weeks. The young are very pale and soft, and if they fall they get back on, perish, or get eaten by mom. They stay until their first molt, and then must eat, grow, hide, and molt on their own.
Scorpions have had extraordinary evolutionary success and exhibit no end of fascinating behaviors. This remarkable animal is not just a lowly arachnid but fascinating and surprising when viewed for any duration. When we use our watchful appreciative eyes we learn that the word enigmatic should not be monopolized by mega fauna any longer.
Written by ASDM Education Specialist, Catherine Bartlett.