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This post deals with DIY control of scorpions at private residences, specifically in southern Arizona, and primarily outdoors as the only way to prevent worse problems indoors. It does not apply to apartment management, industrial grounds etc – only to homes where the owner has free access to all of the property, can spray anywhere and be out at night with a UV light. The novel “Wallpurge” option, described near the end, involves drilling holes in any block walls.
Another limitation is that DIY “do it yourself” outdoors assumes a fair level of strength and fitness. Anyone can hunt, and that’s valuable. But if you can’t haul a 15 lb spray bottle around your yard for an hour, and get the top off to refill it (not easy; see later), knowing where and what to spray will only help if you can hire someone else and “direct it yourself”.
Even if able, should you DIY? The only real alternative is monthly treatments by a professional exterminator. The pros aim at keeping scorpions out of your house for 31 days. Too weak a pesticide or too little coverage and they’ll get a call-back, at their expense. Too much of either equates to overspending on time and materials. The shops must play the averages, with treatments that only incidentally reduce the outdoor population. Pro treatments over one summer will cost about the same as thorough DIY. Neither is cheap. But DIY can in two seasons reduce your entire scorpion population to a negligible level and – at much less ongoing cost – keep it that way. Plus you get to kill them yourself.
There is very little reliable info available to the average person intent on DIY scorpicide. Much of what’s found is impractical, inconsistent or even contradictory. “Pro exterminator” and “DIY” advice often differs significantly because the basic interests, goals, and resources of these two groups are not the same. For example, pros will push “home sealing” (a money-maker if nothing else) but don’t discuss hunting (economically impractical for them). They’ll spray but can only guess at where to do that.
Then there are DIY web commenters and even state agriculture branches saying that “spraying will have little effect”! Well, no single technique does have much effect on a scorpion population, especially if pursued only nominally. Both hunting and pesticides are essential to controlling them at the residential level.
This post summarizes Scorpiomorte’s research and experience. Some repetition is unavoidable because topics overlap, so look over the whole thing before getting into this. Products and possibilities not mentioned (eg. diatomaceous earth) are omitted for a reason; Scorpiomorte does not have time to explain useless stuff too. This post will occasionally be updated to reflect new info, correct errors etc.
Arizona bark scorpions are the target here. These hibernate during the winter, typically in groups. Expect first contact at the beginning of April, with game over by mid-October. This will vary and many other estimates can be found.
Fortunately for us, scorpions fluoresce or “glow” under ultraviolet (UV aka “blacklight”) so those in the open are easy to kill after dark. Pesticides traditionally applied are much less certain but have far greater reach and a long-term benefit from their residual. However, bark scorpions have small bodies, slow metabolism, and typically feed on bugs nearly their own size or larger. After such a meal a scorpion may not need to hunt again for a week. Thus there may only be two dozen chances in the entire season to kill or get residual poison on any given adult, with even fewer for the young that appear meanwhile.
So aggressive hunting and maximal spraying are both important to final victory over the invader. Each of these will have a noticeable effect, but you need the combination to get control of the situation to begin with. Once you have cleared the property, maintenance won’t be as hard; see the Migration and especially the Wallpurge sections below. Note that this post often uses “spraying” as a synonym for “treating”, which includes spreading dust and granules; exceptions should be clear from context.
Pesticides are also the only way to eliminate “food bugs” such as crickets, beetles and roaches. These are the scorpions’ natural prey. If these populations are reduced the scorpions will have to hunt more frequently, stay out longer, and range further – and thus be more exposed. Scorpion predators such as lizards will also be affected by a food bug shortage and so more often on the prowl. All the chemicals used against scorpions are also lethal to food bugs, so it’s actually a parallel campaign.
Start treating at or before the beginning of your scorpion season, and hunting soon afterwards. We all know from sci-fi movies to kill the bugs before they can reproduce. “Them!” (1954) makes a vivid case for this, though in reference to monster ants. Adult female scorpions can have around two dozen offspring during the season. After birth the young are carried on the mother’s back for a couple of weeks; these don’t fluoresce until their first molt at which time they set off on their own. So a bulky adult with a dark back is literally the mother ship and a top-priority target. Many females won’t mate, and not all their young survive, but a maximum effort early on will be far more effective than the same attention later. Also, if the supply of food bugs is already dropping at this time, the scorpions may even eat their young. We can hope.
Precautions are necessary. Always wear safety glasses! These will save you from pesticide that sprays out the wrong way, and from branches semi-invisible at night and even harder to beware of while you’re locked in mortal combat. When working with pesticides you should also have gloves, long clothes, and a filter mask.
To recap: hunting will kill many scorpions and reveal where they tend to hang out; then we apply pesticides based on that though more widely and in depth – a coordination only possible with DIY. That combination is so effective that putting down any appropriate pesticide, combined with regular hunting, will eventually get you most of what all the following advice, techniques, and product recommendations can accomplish. Still, there’s a lot more to say in the interest of getting the most for your efforts and money, and of completely and even permanently resolving a scorpion problem. No pro will do that.
HARBORAGE AND FEATURES
The concrete block walls bordering many Arizona homes are infamous for harboring scorpions; outdoors, this is where you’ll see them first. Such walls have a large thermal mass and remain comfortable for the scorpions day and night. The hollow block design, and how they’re joined, result in narrow cracks leading to large cavities within. This is ideal for the scorpions since anything that can get in there with them is a free lunch. The long, high wall surfaces tend to corral food bugs, especially flyers and in corners. Scorpions prefer hunting from vertical cracks, and for all these reasons will most often be seen lurking near a block wall pilaster (pillar) seam, with the next most favorite spot being the base of a wall.
Block walls are of prime importance and discussed in more detail at the end, with pictures and the novel “Wallpurge” approach. Always try to hunt and treat (spray / dust) both sides of each wall. Get your neighbor’s permission to do this even if you can’t convince them to hunt. If you see scorpions on your side of the wall, a blacklight will show the same on theirs; this is very persuasive. In any case, spray every wall gap and very thoroughly along the wall base. Gap treatment can include dust as discussed later.
Other favorite harborage is under concrete slabs, tiles, and rocks. Always check near these when hunting, and spray into all seams, around the base of each rock or tile section, and along the ground junction of all concrete works. Use the sprayer tip aggressively and watch where liquid drains away, to identify hidden cavities. Lift and spray beneath any movable item. Pro sites recommend spraying the lower part of your house walls; that may be worth doing although once you gain some traction with yard control you will rarely have a scorpion make it that far. Large spreads of very coarse gravel (3/4″ or larger rock size) may be better treated with granules; see below.
Sealing seams between concrete slabs eg. patio-house or on the driveway may sound useful but it’s much easier and probably more effective to simply spray into them. All slabs have large cavities underneath with endless routes for all kinds of bugs to relocate. Seams enable us to hit the cavities and interdict those paths with poison.
Dense, wide-spreading bushes and plants can be impossible to hunt through and difficult to spray thoroughly; these are of special concern if close to a block wall. A scorpion staying deep within such a refuge can “work from home” and not even know there’s a war on. Give them the good news by poking the wand in horizontally at ground level and spraying all around the base of every plant. Get in as far as possible and under leaf trash etc. This is one reason you need a sizable sprayer with a 3′ wand. Best is to remove lower branches so nothing touches the ground. Any plant cluster too dense and inaccessible for spray can be treated with granules or, in the last resort, removed.
Web advice is heavy on clearing out yard clutter. The pros push that idea primarily because treating features of any type absorbs their time and pesticide. Flat bare ground would be ideal, and you don’t want a pile of stuff so extensive that scorpions can find enough food deep within to never emerge. But removing stacks of wood etc. is less important for DIY because you can get those in many rounds of spray and that’s where scorps are likely to hide. If there is good spray access then an accumulation could be useful; some folks create ambush harborage with wetted burlap bags, old rugs, or plywood sheets. Scorpiomorte simply removes the most minor things and sprays in, around and under what’s left.
HUNTING – “Mano a nano”
Blacklight hunting is important because it will directly eliminate many of the enemy and indicate where they’re coming from. Anyone can do this and it’s certainly the most simply effective DIY technique.
Scorpiomorte hunts with a spray-can of automotive carburetor or brake cleaner. Its knockdown beats any pyrethroid and it requires no prep, is convenient, portable, widely available, and cheap. The can’s spray tube is perfect for everything from tiny cracks to nailing a scorp four feet away. The solvent blast is lethal, even at a distance, because it can bowl the bug over and wet its vulnerable abdomen. And a good lathering will kill any young aboard as well, whereas these can get away if you just whack the adult. Of course indoors you’d want a labeled “scorpion spray” instead, to be safer all-round. And these automotive products are just for hunting; they aren’t the “pesticides” discussed elsewhere here.
Scorpions will begin to appear about an hour after sundown and can be found out as late as 3 AM. If you can actually hunt several times a night, great. If you can only get out once and your schedule is open, vary the time within that range. More realistically for most folks, aim for two hours after sundown; earlier only if necessary. By then most scorpions with dinner plans will have emerged.
Hunt every night if possible because scorpions seem to appear randomly. They reportedly come out less in moonlight since that (1) increases their own risk and (2) reduces their advantage of finding victims even in complete darkness, by sensing vibration. However, some will wait near a porch light, possibly attracted by the beating wings of flying insects. The main point is that any one scorpion may only be exposed once a week, plus we really need clues to where they’re living.
It helps that scorpions typically stay within a few yards of their current refuge and often return to nearly the same places. Some find a perfect cavity with a slit entrance near a common bug path, exposing only a claw tip as they wait in ambush. A few scorps will sashay out into an open yard, and may eat a catch right there rather than drag it back under cover. All to the good… in Scorpiomorte’s yard “there are old scorpions and there are bold scorpions; but there are no old, bold scorpions”. Conversely, a small number will scamper off at the first flash of blacklight; be sure to come back for those later because such dangerous behavior must be nipped in the evolutionary bud. Watch for little ones too; fortunately, even those only 1/4″ long are old enough to fluoresce.
Surgeons and pinball wizards may disdain hunting with spray, preferring the über-DIY technique of snatching up the scorpions with tweezers. But most of us will flub that and lose the bug altogether. Or it may be tiny or out of reach. Better to hose it down with solvent and see it die; plus then you can set the scorpse on fire, watch it burn to a cinder, and stomp the ashes. Relax… just kidding. Just.
• Safety glasses which are required. Don’t take chances. For elite status get the amber “UV” type which may enhance scorp visibility under blacklight.
• UV blacklight of course. Almost any one will do but the bigger the spot the less you have to search around. This matters when you’re covering large areas every night. And the brighter it is, the more a scorpion will stand out. Get at least a 12-LED version. In fact get a pack of them and hand some out to your neighbors; they’ll be more inclined to participate after a good look at the glowing little horrors. A 100-LED light is great but you’ll need rechargeable AA batteries and a charger. It will be a nice, hefty reminder of how serious you are.
• Carburetor cleaner as mentioned above. Formulations vary and some brake cleaners will work as well. The key ingredient is probably toluene. Scorpiomorte gets the weaponized “highly flammable” stuff.
• Long-reach (eg. 12-inch) tweezers, for picking up scorpions. Never touch one with your hands, even if gloved. An Az bark scorpion is certainly dead if it’s fully tango uniform with the tail flaccid or out straight… until one isn’t quite dead and nails you. Not worth it.
For further elite creds put a dab of yellow fluorescent paint on the tweezer tips; this will help when using them under blacklight. The first few times you hunt, carry a waste bag and tweeze up yard junk that fluoresces. Otherwise it will cause constant false alarms and distractions. For the same reason, bury or retrieve any scorpions you kill – foregoing the primal satisfaction of grinding them to bits under your heel. That feels great but you’ll regret it every round thereafter.
Some urge capturing the scorpions to ensure that no young escape. Enough carb cleaner will make that concern moot. But for those into zero-carbon paleo, Scorpiomorte does acknowledge the master combo of “Tweezer Snatch With Kilimanjaro”. That’s where you quickly toss the scorp and any progeny into a glass jar and leave them to cook in the sun next day.
SPRAYING and PESTICIDES
This is a huge and very fuzzy topic, so recommendations first; optional background later. More info on equipment is in the Sources section.
Always wear safety glasses (required), gloves, and a good filter mask for mixing and spraying liquids. Long clothes are smart too. Time the job to finish at sundown, so for one evening the poison will be as wet and fresh as possible when the scorpions emerge. This also reduces the risk to bees, and you aren’t working at the hottest time.
Follow pesticide label recommendations and restrictions on rate and frequency of application. Interpreting the labels is literally up to you since they can’t cover everything but – confusingly – must attempt to. Our goal is to hit all likely areas at the max rate (the mix concentrations recommended below) and max frequency. The latter is rarely labeled; the most restrictive found is two-week intervals in NY state. If a product is not labeled for scorpions you can’t legally use it for them. Doing so won’t have much effect anyway; if it did, the manufacturer would have gone to the expense of registration.
For peace of mind: The only significant ecological risk of the pyrethrin-derived pesticides described here is to marine life. However, such chemicals bind quickly with soil so practically none will ever reach a body of water unless sprayed directly adjacent to one (which the labels address). These pesticides are labeled for bees so don’t spray flowers or any other foliage they visit. Boric acid in granules poses no risks. Indoor treatment is addressed as that can be important at the beginning, before outdoor control is achieved.
• Outdoor Spray Equipment: Scorpiomorte uses a 2.5 gal handheld poly bottle sprayer. These have a screw-top pump cap and a spray wand about 3′ long. You can go bigger if you’re large and fit. A smaller bottle will work but treating a yard with a 1 gal sprayer will be tiring just from the refills required, and the wand will be too short to get far under bushes. Occasionally put vaseline or other lube on the pump cap threads for a better seal and easier removal – but unscrewing the cap can still be difficult. It helps to lay the bottle down next to a curb or driveway edge and kneel on it; then you can use all your strength turning the cap handle. This seems to be an issue with all basic poly bottles and may prevent you from using one. In that case some better-made pro gear might work for you.
• Outdoor Spray Pesticides (#1): Tempo Ultra WP at 50 grams of powder per 2.5 gal batch. Each batch also gets 1 oz of Synerpro PBO 91% liquid. Cost is about $10 per batch.
• Outdoor Spray Pesticides (#2): Bifen XTS (not Bifen IT) at 1.5 oz liquid per 2.5 gal batch. Each batch also gets 1.5 oz of Synerpro PBO 91% liquid. Cost is about $4 per batch. This is a great value and can supplement or be alternated with mix #1, especially for treating cavities, but don’t rely on this alone.
• Outdoor Granules: Talstar Xtra, for very coarse gravel (above 3/4″), river rock, dense vegetation etc. Use a hand spreader for this.
• Indoor Spray Equipment: Here a 1 gal poly bottle sprayer works well. You won’t be using as much liquid and maneuverability is important.
• Indoor Spray Pesticides: Cy-Kick CS at 2 oz liquid per 1 gal batch. Each batch also gets 0.5 oz of Synerpro PBO 91% liquid. Cost is about $6 per batch. Don’t stock up on Cy-Kick since you won’t need much of it nor for very long. Also, in a garage or other large, ventilated area where a strong but temporary odor is acceptable, the much cheaper outdoor mix #2 above can be used instead.
Mixing: First put a few inches of water in the spray bottle, then the pesticides, then (wearing your mask!) more water to reach the max fill line. Screw the pump cap on, shake the bottle well, and pump it up as much as you can or until the relief valve begins to hiss.
Spraying rate is difficult to gauge. Official guidance is on the pesticide label. In practice, Scorpiomorte picks his targets (most open areas needn’t be sprayed) and lays down enough to fully moisten those surfaces. The same spots will receive many treatments during the season (right?) so no need to get them dripping wet each time. Indoors, spray along the base of walls, into any cracks especially near entrance doors, under appliances and in the back of cabinets etc. Garage floor seams are worthy of special attention.
It’s OK to keep a mixed pesticide spray for at least a week, in a dark area. To further slow any degradation you can add one tablespoon of vinegar per gallon.
• Dust Equipment: Scorpiomorte reluctantly uses the primitive, clunky, crudely built and gloriously overpriced “CentroBulb Duster” with extra-cost 12″ extension. Goggles and a respirator (not just safety glasses and a dusk mask) are highly recommended.
• Dust Pesticides: Delta Dust or D-Fense. Both are 0.05% deltamethrin. See the separate discussion below on dust.
As a supplement, consider targeting food bugs directly with Niban granules. Niban’s only active ingredient is orthoboric acid so it can be spread much more freely than pyrethroids, covering open areas. Boric acid’s effect on scorpions is so minor that it’s rarely labeled for them. However, it is good against crickets and cockroaches, and may help with beetles. Niban includes a spectrum of attractants and has significant residual action / persistence. A couple of heavy treatments each season should usefully reduce the scorpions’ food supply, and incidentally many types of ants.
Background & General Moan (completely optional)
There is no solid information available on the best pesticide for scorpions. After seventy years of ever-increasing attention, and countless or more studies on pyrethroids, only two field trials are found that (very broadly) compare the effect on scorpions of a few (older) poisons. Manufacturers have real data on this, of course, but their reports are proprietary with only the barest facts released. Governmental and therefore academic interest is entirely focused on the environmental impacts of these chemicals, not on their efficacy and even less on differences in that. The tiny percentage of comparative studies published are almost always concerned with pests affecting health (eg. mosquitoes) or food production (eg. beetles).
We only know that if a pesticide is labeled for scorpions then it has, to the EPA’s satisfaction, been shown to kill a significant percentage of them when used as directed. Under what conditions it kills, and how fast, and for how long are impossible for the layman to determine. Also consider that if a poison is truly superior in lethality, its AI (active ingredient) concentration in the retail product will be reduced to make the final mix comparable to the alternatives. Examples are beta-cyfluthrin replacing cyfluthrin, zeta-cypermethrin vs cypermethrin, gamma-cyhalothrin vs lambda-cyhalothrin, and esfenvalerate vs fenvalerate. That’s because the EPA controls all of this, and they have no interest whatsoever in your bug problems. Their job is to (1) determine what environmental damage each poison does and (2) prevent people from spreading more of it than necessary. So there – that’s what we pay them for. But it does leave us dependent on manufacturer blurbs, distributor advice, professional practice, anecdotal evidence, and what we can guess about residual action, degradation, synergist boost, surfactants, etc.
To help sort this out, Scorpiomorte distinguishes between chemical lethality and vehicle effectiveness. These are ad-hoc terms, not from the industry. As noted, lethality is apparently normalized: if chemical A is really better than B, you’ll get less of it in the allowable dose. So there’s little to be gained from comparing lab results of A to B even where available. That said, the cyfluthrin group does appear to have some advantage with scorpions.
Another red herring is “knockdown”. This originally signified immediate and lethal impact, but its legal meaning now seems to be “eventual incapacitation”. A pesticide can have prompt, visible knockdown if it hits the bug just right; or a days-later knockdown via the residual. In practice every pesticide out there will have some degree of test lab knockdown because it couldn’t otherwise be sold. Equally irrelevant here is “flush-out” which is the ability of a chemical to excite the bug, making it run around and pick up more poison. Spreadable area pesticides that are labeled for scorpions and tout these powers are slyly misleading… they’ll knock down and flush out other bugs, but only gradually affect a scorpion. That’s unless you hit the abdomen (see below) when treating, which is pretty unlikely. So ignore these terms – we’re concerned with residual action.
Thus, we can’t do much about lethality. That leaves the vehicle ie. whether the chemical is delivered via an emulsion (EM), a suspension (SC), wettable powder (WP), water-soluble packets (WSP), powder / dust, granules, or maybe other forms, and if it’s micro-encapsulated (ME). Here too there’s little data and some normalization, but it does help to consider our specific target and environment.
The scorpion season in southern Arizona coincides with very high temperatures and intense sunlight. This is interrupted by a few weeks of occasional heavy rainstorms aka “monsoon season”. Unfortunately, all of these factors weaken the effect of pesticides, as does the fact that most outdoor surfaces are very porous.
Also important are scorpion physiology and habits. These bugs are not only highly efficient predators but also well-protected and tough as nails. Pesticides have no effect on their backs, but only through the less-protected membranes in the abdomen – which scorpions try to keep off the ground. The other avenue is via the mouth during grooming, but that’s infrequent, and digestive fluids combine with the low metabolic rate to retard toxic effects in this path. PBO (see below) will help here.
Cost is a concern. A serious DIY effort will be personally time-consuming in any case, so it’s misguided to use the cheapest chemicals (eg. permethrin) which are generally the least residually effective. And DIY results will be at least as good as weekly pro treatments, which is presumably the limiting option since those who can afford that are not likely up for DIY anyway. So we’re looking for value but within the higher product range.
• Outdoors prefer wettable powder (specifically Tempo Ultra WP) because it (1) will have a better residual on exposed porous surfaces than even ME mixes; (2) contains beta-cyfluthrin; (3) can get into the places scorpions go (block wall sides and cracks) where granules won’t; (4) is much more easily applied than dust; (5) will be more quickly lethal than dust; and (6) can carry PBO (see below). Bifen XTS is much cheaper, especially if you omit the PBO, but has noticeably less residual effect on exposed surfaces.
Exceptions outdoors are large, dense, inaccessible plant clusters, and large areas of gravel so coarse that scorpions can remain beneath it. For these, granules can get through to the ground whereas most spray will simply lie on top to little effect. Talstar Xtra contains bifenthrin and zeta-cypermethrin, both reasonable choices, and has a long residual. The label does not call for watering but doing so may activate the product more quickly and will help move the granules to the ground.
• Indoors prefer a microencapsulated suspension (specifically Cy-Kick CS) because these will do well on the generally less porous surfaces there. This product contains cyfluthrin to which we add 4x PBO. Bifen XTS is again much cheaper, even with PBO added, but has significantly less residual effect and its oil base will smell for a few days; a good use for it is garage floor seams.
“PBO” is piperonyl butoxide, primarily used as a synergist. PBO upsets the bug’s digestive process, reducing its ability to degrade an ingested pyrethroid. Because it strongly absorbs UV light, PBO may also sacrificially extend the outdoor half-life of the pyrethroid. PBO has low toxicity and liberal application allowances. Its synergistic benefit pertains up to a PBO AI of about 9x the poison’s AI. In practice PBO’s cost will limit our use to around 5x, considering also that it may be of no help to poisons absorbed through the abdomen. Still, this is the only way to directly increase the potency of our pesticides.
“Dust” refers to a very fine white powder based on deltamethrin and commonly called “delta dust”. Like all pyrethroids it can only kill scorpions by getting inside the body. Delta dust seems very well suited to this due to its tiny particle size, which should also help it stick to the scorpions legs etc. and later be ingested via grooming. With a bulb duster it can be blown through tiny cracks and will then float along into hidden cavities. Also, when not in direct sun or water, deltamethrin has a relatively good half-life. Many pro exterminators highly recommend dusting cracks and crevices, especially block wall seams. A few scorn the stuff because it’s avoided by scorpions and very slow to affect them. Scorpiomorte uses dust but only when first treating a yard and only in block walls where its penetration ability is obvious, it won’t degrade fast, and the target population is numerous, confined, and hard to reach by other means. Doing this thoroughly just once or twice is enough. Treat every opening the thickness of a credit card or larger. When in doubt, dust. Stick to plain 0.05% deltamethrin dust (Delta Dust, D-Fense), avoiding any with desiccant (Drione) which adds nothing for scorpions. Wear a respirator and goggles because a little dust literally goes a long way. If the wind turns you’ll be breathing in a cloud of it.
Some say treatment is pointless unless coordinated with any neighbors because the scorpions will just move between properties. This effect is overstated. It is true that treating an area will reduce its population of food bugs, making it less attractive to scorpions and forcing them to hunt elsewhere. Also, scorpions can detect some poisons (eg. delta dust) and in avoiding those will naturally range into other areas. But – except for tiny scorpions possibly being wind-blown – they don’t relocate quickly overall. Instead it’s a slow process of move a little, test for food and harborage, and repeat. Sighting scorpions on and apparently traversing block walls can look like relocation when in fact they simply prefer the walls for other reasons, and happen to be very visible on such surfaces. If your neighbors aren’t treating, the long-term effect of your work will be dampened because some scorpions will move out of reach and can later return. But if you at least keep treating your borders (or implement Wallpurge – see below) and reducing food bugs, scorpions won’t come back in force. Eventually your neighbors will be treating too and, regardless of their perception, you will have helped them by reducing the number of breeding scorpions in the whole area. That’s what really matters.
Cats may have some value against scorpions indoors, but outdoors they are a negative. Their favorite prey is lizards (far more than birds, though leaving much less evidence) which removes an important scorpion predator.
Remarked elsewhere is that chickens will get rid of scorpions – but then you have chickens…
WALL THINGS CONSIDERED
A block wall around your yard is the single most important physical factor in scorpion control. Understanding wall internals reveals the problems and opportunities involved.
Standard concrete block fence wall construction lays the blocks in a staggered fashion, as seen in the pictures below. Hollow cells in each block line up over cells in the blocks above and below, shown in the cutaway view. This creates vertical “cores” or columns, which run like chimneys from bottom to top. Some of these cores are filled with grout to hold rebars, but most remain empty air shafts. Also, pilaster facings may have nothing behind them, which creates more large air columns.
Sun Tzu said “Who owns the columns owns the wall. Who owns the wall wins the war.” In other words, control of the air columns is key to the wall being a negative or a positive feature. That’s because (a) walls surround a property and (b) scorpions can’t resist them and / since (c) access is so limited.
As built, walls are a negative since we can only get at the air columns behind pilasters, via their vertical seams. Other gaps are largely unhelpful. Most are in ‘head’ joints, which unlike ‘bed’ joints are often left unmortared. With the common two-cell blocks, the resulting vertical gaps will line up with the internal ‘web’ or cross-wall of the blocks above and below. As a result, these gaps will be of little use in getting pesticides into the air columns. They just make it easier for scorpions to move internally and externally. Faults in bed joint mortar will usually connect directly to an air column, but such gaps are random and too rare to have an effect overall.
This has implications for wall sealing as well as spraying. In particular, don’t seal just one side of a wall unless the other side is accessible for treatment. Probably only a complete stucco covering of both sides of a wall, including top caps, would physically prevent scorpions from using it. Stucco must be checked later for cracks due to settling, and unavoidable gaps at the base must still be treated. Such a coating will be expensive even when it’s practical.
Positive Thinking: “Wallpurge”
Key fact: in a typical backyard with an unsealed block wall surround, the majority of scorpions will either harbor primarily in the wall or visit it periodically. Hence the recommendation to spray the wall base frequently and heavily. Robust treatment is needed because even with wettable powder (eg. Outdoor Mix #1) the residual effect on ground (next to the base) and the vertical wall side will be reduced by runoff, sunlight, and especially by rain.
Much more aggressive is to use the wall as a trap! This involves taking control of all the air columns, including those normally closed off. Fortunately this can be done cheaply, and from only one side, by drilling small (eg. 3/16″) injection holes in the highest bed joint of each internal core column. There’s a picture below. It’s a lot of work with masonry bits and a hammer drill, but afterwards you can easily and thoroughly treat every cavity not already accessible via pilaster seams and caps. The wand spray tip can be removed and the tube end applied directly to each hole, with a reducer if needed. The economical Outdoor Mix #2 can be used since the pesticide will be shielded from the elements, with maximum residual. And – it can’t impact the environment. Maybe complement this with dust. An alternative is to drill lower down on the wall; pesticide injected at that level won’t cover as much of the internal volume, but will be effective and the holes will be less visible. A fallback is to drill only one access hole per block i.e. skipping every second air column; this relies on imperfect joints between the block webs and other parts permitting the scorps to circulate and pick up poison eventually, and could be considered for a first-year trial.
Scorpiomorte calls this active perimeter defense “Wallpurge” after Saint Walpurga, an early exponent of such tactics. It goes beyond wall suppression, creating a boundary bastion belt of beckoning death. Ha! Occasionally refreshed with pesticide, this will eventually kill all existing scorpions within a few feet, and any newcomers. Plus it eliminates a primary meet & mate venue, amplifying the effect on long-term yard population. With some hunting, and thorough initial treatment of other major harborage, Wallpurge can keep your back yard scorpion-free – regardless of neighborhood conditions!
Unfortunately, Wallpurge won’t be practical if your blocks have three or more cells since too many holes would be required. And of course front yards still need conventional attention.
WHY WE FIGHT
This post has avoided filler facts but scorpion stings are relevant and people report widely differing experiences, to general confusion.
Venom is metabolically expensive for a scorpion to produce and very important to its ability to capture prey. Scorpions therefore control the amount injected with each strike, using as little as seems necessary. Their exceptional vibratory senses can easily distinguish between the approach of a meal bug and that of something human-size. The latter has no potential food value and must be driven away, not closely engaged.
So if you step barefoot next to a scorpion, you’ll get one strike with minimal venom. The scorpion correctly figures that’s enough to get rid of you. Your foot will feel like it was stung by a large electric bee. But the pain won’t be debilitating or even keep you awake that night, and will be fading away in 24 hours.
Things will be very different if you step right on the scorpion. In desperation it will sting repeatedly and with far more venom, totaling perhaps 20 times that of the first strike. Your foot will be on fire for at least a day, you won’t be walking anywhere for a couple more, and might be in the hospital.
The small sting is bad enough but the chance of getting the deluxe treatment makes it imperative to keep scorpions out of our homes.
ICANN web rules require scorpion posts to have at least one creepy picture, so here’s an Arizona bark scorpion molting. Fittingly for this site, it died in the process. The old skin still fluoresced whereas the new bug didn’t yet, making for a grim sight under UV.
Amazon is good for equipment. Some specifics there (as of 2018) are:
• Dewalt DPG82-11 safety goggle
• Amston Dust Masks N99 NIOSH-Certified (for spraying)
• 3M 07193 Dual Cartridge Respirator (for spraying or dusting)
• iLumen8 amber blacklight shooting glasses
• SE TW2-403 Stainless Steel Tweezer Set 12″
• CentroBulb Duster with 12″ extension
• SKIL 6445-04 7.0 Amp 1/2 In. Hammer Drill
• DEWALT DW5222 3/16-Inch x 3-Inch Drill Carbide Hammer Drill Bits
Scorpiomorte is glad to get solid info, especially from pesticide chemists or testers.