Why are there bark scorpions in a desert city that never had them?
Arizona bark scorpions are not native to Las Vegas. They arrived around 1990 with plants imported from Arizona and spread through palm trees and new track-home construction. Around the valley they are more likely to live in block walls and houses than out in open desert.
The story goes back to the landscaping boom. New subdivisions wanted palms, citrus and ornamental plants, and many came from Arizona nurseries. Scorpions likely rode in with the plants, and the valley's block walls gave them an ideal home: a tall, warm, cracked, hollow structure in every back yard.
That history explains why the density can be so high on streets that look nothing like desert. A fifteen-year-old subdivision with a block wall, a rock yard and a drip line is, for a bark scorpion, a good place to live. The same pest turns up in Summerlin, Spring Valley, Henderson and Centennial Hills.
How do scorpions get in through a block wall?
Hollow concrete block is full of vertical cores, and a narrow crack or an uncapped top lets scorpions in, where they can live in large numbers. They then travel along the wall to the house, through weep screed gaps, door bottoms and window frames. Stucco and a solid cap close the wall.
A bark scorpion can squeeze through a very narrow gap. A step crack where a gate post meets the wall, a missing cap block or a hole left by a pulled sprinkler pipe is enough. Inside the wall, the cores are warm, dark and protected, and insects wander in to feed.
From the wall to the house is a short trip. The weep screed at the base of a stucco house leaves a small gap by design, to let water out, and scorpions use it. Door sweeps that have worn thin, window screens that do not fit the frame and the seam between the garage floor and wall do the rest.
When are scorpions most active in Las Vegas?
Bark scorpion sightings rise from spring through early fall, peak in summer and stay high in September, which is one of the most active months. Spring and autumn are mating seasons. They go inactive in winter as nights chill, so a January sighting is unusual and worth checking for a warm indoor harborage.
Heat sets the clock. As March and April warm up, sightings begin to climb, and by July, when highs average near 106 degrees, scorpions are at their peak. Many people assume activity drops in the worst heat. In practice the animals move at night and shelter in walls by day, so you meet them after dark.
September surprises homeowners. The summer is over on the calendar, but scorpions are still among their most active, and the monsoon's tail can push them toward doors. Late autumn, as nights cool, is when sightings finally thin out. If you plan one treatment a year, early spring ahead of the climb is a reasonable time to talk to a technician.
What happens during a blacklight scorpion inspection?
After dark, a technician sweeps a handheld ultraviolet light along block walls, the foundation, rock beds, patio edges and the garage. Scorpions fluoresce under the light, so the light shows what you cannot see. Treatment follows where they were found, and you get a list of gaps to seal.
Blacklight work is why scorpion calls are often scheduled for the evening. In daylight scorpions are hidden in cracks and under rock, but at night they come out to hunt and the light picks them out. Your technician can show you where the animals were and how they were moving.
That gives the treatment a map. A pest company that sprays the lawn and walks off has not found the wall crack where the colony lives. A technician who finds the glow along a particular stretch of block wall can treat that stretch and tell you which cap, gate post or stucco crack to fix first.
