Keeping them out

Spraying reduces the population. Sealing decides whether they get inside. A bark scorpion passes through a gap about 1/16 of an inch — roughly two credit cards — so the standard is tighter than it sounds.

Start with the garage door

The single biggest opening on almost every Havasu house, and the reason so many scorpions turn up in garages. Concrete is never dead flat, so the rubber seal bridges the high spots and leaves gaps at the low ones.

Close the door at night, stand inside, and shine a torch along the bottom from the inside. Any light you see is a doorway. A threshold seal glued to the slab — the raised strip the door closes against — fixes what a new bottom seal alone will not.

Then the things a slope adds

These are the ones a flat-lot checklist misses, and on a tiered Havasu property they matter more than anything else:

• The cut face behind the house. Where the lot was carved into the hill there is exposed, fractured rock, often within a few feet of the back wall. That is the primary harbourage, and no amount of work at the front door touches it.
• Retaining wall bases. Every tier has one. Treat the base of the wall nearest the house first — that is the corridor they travel.
• Weep holes and drainage gaps. Tiered lots are full of drainage that must stay open. Do not caulk it — you will trap water behind a wall. Stainless weep screens or bronze wool let water and air through and stop arthropods.
• Stem wall at the downhill side. On a sloped lot one side of the house sits high off the ground. The gap under it is a covered highway.

The standard list, still worth doing

• Door sweeps on every exterior door, including garage-to-house.
• Copper or stainless wool plus sealant around hose bibbs, AC line sets, gas and conduit penetrations. Steel wool rusts away in a season.
• Check window frames are still caulked to the stucco — original beads crack and pull away in this heat.
• Amber porch bulbs instead of white. Fewer moths and crickets means fewer scorpions coming to eat them.

Landscaping: the eighteen inches that matter

Nobody is going to strip the rock off a Havasu lot, and nobody should. What changes the outcome is a clear strip at the foundation:

• Eighteen inches of bare ground between decorative rock and the wall.
• Nothing stacked against the house — spare pavers, block, firewood, pot saucers, kayak racks. Each is a staging area.
• Trim anything touching the roof. Bark scorpions climb, so an oleander resting on the eave is a bridge over every seal you installed. This is the usual reason people find them upstairs.
• Fix drips. Leaking bibbs and AC condensate create the damp strip where crickets breed, and crickets are the reason scorpions are on your wall.

What honest exclusion achieves

A thorough job on a typical Havasu single-storey takes a technician most of a day and costs a few hundred dollars. It will not get you to zero — the hillside behind you keeps producing. It reliably turns "two a week indoors" into "one every few months in the garage", and unlike a spray it is still working next summer.