By Tina Mitchell
The dog stood still as a statue, nose to the floor. Maybe he was watching an insect. But usually he’d just check it out and move on or else snarf it down. This behavior was different. Curious, I walked over. Uh, oh – the boy had zeroed in on a scorpion. A first for us both. But over our 15 years in that house, we found a number of scorpions inside, especially in the winter. We eventually realized that most arrived on the firewood we stacked near the woodstove. When we moved the stack to the garage, the number of winter-visiting scorpions dropped.
Scorpions fall in the class Arachnida, making them distant cousins of spiders. Some people think that arachnids are insects – not so. Insects have six legs and three body segments (head, thorax, abdomen) while arachnids have eight legs and two body segments (cephalothorax – a combined head and thorax – and abdomen). Three species of scorpions call Colorado home; the most common one in central Colorado is the striped bark scorpion (Centruroides vittatus). In fact, the striped bark scorpion is the most common species in the U.S. It grows to 2.75 inches long, with two dark stripes down the length of its back. A scorpion has an elongated abdomen that ends with its signature stinger, often curled over its back. Its enlarged appendage-like pedipalps on the cephalothorax form claws for grasping prey. Also on the cephalothorax is a pair of simple eyes at the midline and 2–5 pairs along each side. Its light tan or yellow color suits its environment well, providing natural camouflage from both prey and predators. C. vittatus has a very dynamic diet, including fast-moving insects and smaller arachnids. In turn, it finds itself on the menus of birds, reptiles, some mammals, and even larger arachnids.
The scorpion’s stinger provides only a modest defense mechanism, since its venom has low toxicity. While a C. vittatus sting is not serious for most humans – similar to a bee or wasp sting – several other Centruroides species can deliver a deadly dose. But no species found in Colorado has venom routinely associated with dangerous complications.
“Bark scorpion” suggests that this species hangs out in trees (or under the bark of wood for the wood stove). But striped bark scorpions spend considerable time on the ground. During the day, they lurk under loose rocks, dead wood, and other protected sites such as (at least at our house) in the cool, damp soil under the ground-level birdbath. Scorpions can be surprisingly easy to find at night, if you have an ultraviolet (“black”) light. The exoskeleton of a scorpion has a chemical structure that causes it to fluoresce in ultraviolet light.
A striped bark scorpion fully matures in 3–4 years and may live 2–3 years more as an adult. Following a gestation period of up to eight months, young striped bark scorpions (called “scorplings”) are born live – in Colorado, primarily from June to August. They travel on the mother’s back for 1–2 weeks until their first molt (a stage of growth called the first instar). Litter sizes range from 13–50. After the first molt, the young begin to forage on their own. Subsequent molts of the exoskeleton (instars 2–5) occur in response to growth. I used to startle myself by coming across a very still scorpion in the house. As I’d creep up on it to escort it outside, I’d eventually realize that I was stalking a shed exoskeleton. Swell. A new instar of scorpion lurked somewhere in the house. Time to start shaking out shoes before donning them.
Some people really dislike these tiny predators, but they prefer to leave humans alone. Well, unless you’re the mythological hunter, Orion. A goddess sent Scorpius the Scorpion to kill Orion after he had boasted that he would kill every wild beast. Since these constellations appear opposite each other in the sky, some say that Orion is still fleeing Scorpius. In Colorado, you need a clear view of the southern horizon to see Scorpius as it skitters just above the summer horizon. In early July, look to the south for Scorpius’ “pedipalps” (looking a bit like the numeral 7) around 11 p.m. MDT; look there ½ hour earlier with each passing week into mid-August.
So this summer, keep looking up – and down – for scorpions.
After a quarter-century in Colorado, Tina and her family recently migrated to Southern California, where she’ll spend the next quarter-century trying to remember that the mountains lie to the east.