Striped Bark Scorpions in Texas: Taxonomy, Anatomy, Behavior, & Case History 1

— This article by Jerry Cates, first published on 6 June 2011, was revised last on 23 October 2013. © Bugsinthenews Vol. 12:06(01)

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Taxonomy & fossil record:

• The striped bark scorpion (Centruroides vittatus) was first described by the American naturalist and entomologist Thomas Say (1787 — 1834) in 1821. This scorpion, and all other scorpion species, are arthropods (invertebrate animals with jointed appendages) in the class Arachnida, a class first described in 1812 by the French naturalist and zoologist Jean Léopold Nicolas Frédéric Cuvier (1769 – 1832) using the Greek noun ἀράχνη, a-‘rach-ne = “spider.”
• Scorpion arachnids are further placed in a unique order, Scorpiones. This order, which in early 2011 contained about 1,750 recognized species, was first described by the German entomologist and arachnologist Carl Ludwig Koch (1778 — 1857), using the Greek noun σκορπιος, ‘scor-pi-os = “scorpion.”

The scorpion depicted in the first three photographs, and in the first montage below, was collected in central Texas in 2005. It is a gravid female, whose young were approaching full development in the womb.

• Scorpions are well represented in the fossil record, dating from the Silurian period about 430 million years distant. Silurian scorpion fossils are of marine animals with gills. Modern scorpions are terrestrial, with book lungs.Except for this and a few other, relatively minor anatomical differences, the modern scorpion and its 450-million-year-old ancestor are remarkably alike: “Modern scorpions are generally similar in appearance to Paleozoic forms. Except for the changes in locomotion and respiration necessitated by the migration to land, the basic body plan is externally similar to that of scorpions that lived 425 million years ago… The earliest scorpions possessed a segmented opisthosoma with the mesosoma and metasoma clearly differentiated, well-formed chelate pedipalps and chelicerae, eight walking legs, pectines (unique to scorpions), and a terminal telson.”  (Polis et al., 1990).
• The lack of significant changes over the past 425 million years is considered proof that scorpions did not need to evolve in radical ways in order to thrive: “Evidently this early body plan was a particularly successful one, sufficiently general and well adapted that major changes did not subsequently occur. Thus, no great architectural revolution in external morphology accompanied the taxonomic diversification of scorpions into the various extinct and extant families. Neither has there been extensive modification during radiation into different habitats: tropical species are similar to desert species; intertidal scorpions resemble those from high altitudes. Although some species show ecomorphological adaptation to different soils and microhabitats, similarities in appearance among scorpions far overshadow morphological differences. All scorpions look generally alike.” (Polis et al., 1990)
• Though morphologically conservative, scorpions exhibit exceptional abilities to adapt ecologically, behaviorally, and physiologically. Certain species adapted to northern climates can be frozen for weeks and subsequently return to normal health within hours of thawing. Others, adapted to wet environs, can be placed underwater for 1-2 days at a time, with no signs of ill effects when returned to dry land. Across all species, thermoregulation is mediated by the scorpion’s adoption of behavioral protocols that avoid extremes of temperature and dessication, including, for example, a strong reliance on nocturnal foraging, when stressful temperatures and the accompanying risk of dehydration are much lower. (Polis, et al., 1990)
• Scorpions adapted to arid climes are believed capable of managing body hydration more efficiently than any other arthropod known: their excreta, of essentially insoluble nitrogenous wastes, do not export body moisture. Similarly, the scorpion’s respiratory organs — in the form of spiracles, book lungs, and respiration through the integument — have a role in preserving body hydration as well. Waxy, lipid coatings on the exoskeleton prevent excessive transpiration via that organ. Such efficient economy of body moisture enables some species to acquire sufficient water from the food they consume. Like many spiders (e.g., recluse spiders in the Sicariidae family) scorpions exhibit some of the lowest arthropod metabolic rates on record and — like such spiders — are often able to survive without food for a year or more. (Polis et al., 1990)
• Many scorpions spend more than 90 percent of their lives in a quiescent state. Scorpions have adopted the imminently successful foraging strategy of opportunistic ambushers, loitering in dark shadows until prey comes to them. That strategy, combined with the external digestion of food, enables them to gain as much as 33% of their body weight from a single meal. (Polis, et al., 1990)
• The Buthidae family, within which the striped bark scorpion is now classified, was also described by Koch in 1837. The basis for Koch’s choice of the root Buthid (also the root for the names applied to the superfamily and suborder within which the Buthidae family is assigned) is obscure.
• The generic name Centruroides was first described by the German-born American entomologist George Marx (1838-1895), in 1890, using the Greek noun κεντρον, cen-tron = “a sharp point,” most likely a reference to the scorpion’s stinging telson.
• Buthidae is the largest family of scorpions in the order Scorpiones. Buthids comprised, in early 2011, as many as 80 recognized genera and more than 800 species. They are natives to practically all of the warm regions of the major land masses of the earth, with the exception of the British Isles, New Zealand and Antarctica. They have been introduced to the British Isles and New Zealand over the past century, a consequence of human trade and commerce.
• Within the Buthidae, the genus Centruroides comprised, in early 2011, some 70 recognized species worldwide.
• The specific name vittatus was crafted by Say from the Latin word vitta = “a ribbon or band,” in reference to the longitudinal stripes on the dorsal metasoma (pro-abdomen).

Anatomy:

• All scorpions have bodies divided into two primary sections, and three tagmata (from the Greek noun τάγμα, tag-ma = “that which is ordered or arranged.”)
• The two primary sections of the body are comprised of a six-segmented cephalothorax and a twelve-segmented abdomen.
• The scorpion’s six-segmented cephalothorax (head) or prosoma (fig. 004, above), is covered by a carapace with median and lateral eyes, and bears cheliceral mouthparts, four pairs of ambulatory (leg) appendages, and one pair of grasping (pedipalp) appendages.
• A pair of relatively large median eyes is positioned in the center (middorsally) of the carapace (figs. 005 & 007).
• In the striped bark scorpion, a cluster of three relatively small eyes are positioned at the anterolateral margins of the carapace (fig. 006).
• The twelve-segmented abdomen is subdivided into a seven-segmented proabdomen or mesosoma and a five-segmented postabdomen or metasoma.
• The seven-segmented proabdomen or mesosoma consists, externally, of the following: on segment 1 a pair of genital opercula, on segment 2 the basal plate of the pecten sensory appendage, on each of segments 3-6 a pair of spiracles that articulate individually with the animal’s four pairs of internal book lungs.
• The proabdomen, internally, comprises the primary organs of respiration (the four pairs of book lungs themselves), digestion (corresponding roughly to the mammalian small intestine), and genitalia/gestation (ovaries or testes, and for the female, the ), and segment 7, which constricts the posterior mesosoma down to form the attachment to the scorpion’s five-segmented postabdomen or metasoma.
• The five-segmented postabdomen or metasoma (commonly called the “tail”) contains the primary organs of excretion (corresponding conceptually to the mammalian large intestine) and envenomation (the stinging telson). The anus is positioned at the far end of segment 5, just forward of the stinging telson. The telson articulates with metasomal segment 5, and consists of a large bulb containing venom glands and a venom reservoir, or lumen. The bulbous telson narrows at its far end, where it transitions into a curved, sharp pointed aculeus, or stinger.
• The hardened chitinous exoskeleton of mature scorpions fluoresces a bright lime-green when illuminated with ultraviolet light.
• The fluorescing constituents of the scorpion exoskeleton are known to be associated with a thin, tough, hyaline (from the Greek adjective ὑάλινος, halinos = ‘glassy,’ a derivation of the Greek root ὕαλος, halos = ‘crystal, glass’) layer.
• The hyaline layer includes, among other fluorescing materials, a class of indole alkaloids known as β-carbolines. Many of the β-carbolines are psychoactive, which may partially explain the regular consumption, as a delicacy, of fried scorpions by certain Asian cultures, as well as the use of scorpion wine and related extracts in traditional Chinese medicine.
• The toughness of the hyaline layer of the scorpion exoskeleton is responsible for the preservation of ancient fossil records of this animal. When fossil hyaline is illuminated in ultraviolet light, it — like the hyaline constituents of modern scorpions — fluoresces lime-green.
• When a scorpion molts, as when the nymph emerges from the womb, its softened exoskeleton is not yet provisioned with hyaline, and thus does not fluoresce.
• Besides providing a tough exoskeleton, the fluorescing hyaline layer possessed by scorpions is thought to assist the animal in its efforts to avoid light while foraging and reducing the risk of predation.
• Photo-phobia, mediated by the fluorescing hyaline layer and a poorly understood system of light sensitive photo-detectors in the dorsal exoskeleton of the dorsal mesosoma is suspected to enhance the animal’s ability to hide from predators and prey alike.

The scorpion depicted in the first three photographs below (figs. 100-102), and in the montage below them, was collected at a commercial structure in Buda, Texas on a moonless night, 1 June 2011 (the moon was new, and had already set when the survey began; the sky was clear, and weather conditions were dry and warm). This specimen was one of three observed on this visit, and — as with the first specimen depicted on this page, above — is a female. Microscopic examination of the genital operculum fails to detect the presence of papillae, and the significantly elongated metasomal segments, characteristic of the male, is not observed in either of these specimens.

 

 

• All scorpions are viviparous:
• Young are carried in the mother’s womb throughout gestation and birthed alive and capable of ambulation shortly after birth.
• Gestation periods vary depending on species, lasting in Centruroides vittatus for approximately eight months from fertilization of the egg to birth of the young.
• In comparison with many other scorpion families, most members of the Buthidae family tend to be medium sized or smaller than average.
• Their pedipalps, pincers attached to each side of the face used to grasp and hold prey, are modest in size and strength as well. However, the venom of some two dozen Buthids is notoriously dangerous, to the point that, according to some authorities, fatalities are regularly recorded among humans in certain locales who become envenomated by these animals each year.

Behavior:

• The striped bark scorpion (Centruroides vittatus) is gregarious with its own kind, exhibits a low propensity for cannibalism.
• This scorpion is photo-phobic and thigmophilic in its selection of diurnal refugia, preferring rough, natural textures containing familiar and attractive chemical cues such as are found in ground litter, fossorial burrows, and wood piles over smooth textures — typically containing minimal chemical cues — typical of man-made structures, to hide in during the day when foraging is kept to a minimum (McReynolds, 2004; personal obs.).
• Nocturnal foraging habits of this scorpion are demonstrably photo-phobic. In natural surroundings absent artificial illumination, these scorpions are more active on dark nights, while on nights with significant moonlight they hide in darkened areas where ambient moonlight does not penetrate (McReynolds, 2004).
• In the presence of artificial illumination, they show a marked propensity for nocturnal foraging within cryptic, darkened locales opportunistically populated with insect and arachnid prey from nearby, well-lit locations that attract large numbers of flying insects during the nighttime hours (personal obs.).

Investigatory Case Studies:

The scorpion specimen depicted here was collected on 1 June 2011 in connection with an investigatory study in the field. A commercial structure in a rural, mostly undeveloped area of Buda, Texas, was experiencing a bothersome infestation of striped bark scorpions (up to two scorpion observations, inside the structure, per week), and a survey was conducted to determine where the scorpions were focused in the surrounding environment.

Construction of this structure and its ancillary improvements was first begun over two years ago, suspended for a year due to economic considerations, and finally completed in early 2010. The site provides an excellent opportunity to observe changes in populations of insects and their predators, in this case the native striped bark scorpions, that occur over time after undeveloped mixed woodland/farmland is converted to human occupancy in this portion of south-central Texas.

Previous investigations (see, for example, my analysis of a similar, though more serious, infestation in Cedar Creek, Texas, which involved a 20+ year-old ranch home on 30 acres of densely wooded land) had already amassed evidence suggesting that these scorpions do not ordinarily inhabit human residential structures except for purposes of temporary refugia enroute from unintentional spatial redistributions (e.g., falling out of trees onto the roof during nocturnal foraging expeditions aloft). Though they wander into such dwellings with regularity, such places are not preferred by this animal either for their nocturnal foraging haunts or as diurnal refugia, where they rest during the day until time to resume their foraging activities after dark. Furthermore, at least in the natural wildernesses of Texas unaffected by human activities, it is rare to find large numbers of these scorpions in a single location. They tend to be scattered about in small numbers, probably commensurate with the localized provisions of prey, water, and refugia (McReynolds, 2004).

It is useful to inquire, then, about the factors that cause scorpions to end up in human dwellings. And to ask why, in many cases, their populations bloom upward into enormous numbers to the point that they constitute what some, in the popular media, are wont to describe as “Extreme Infestations.” As with many scientific analyses in the biological world, the answers to these question are complex, and contrary to human intuition. My tentative conclusion, arrived at from field investigations conducted thus far, has three parts:

A. Native populations of striped bark scorpions must first exist in the static environment within which the human dwelling is placed. Obviously, without the presence of a native population of such scorpions, we would never see them in human dwellings in the first place. Yet, even with the presence of native populations, under ordinary circumstances the number of scorpions involved — at least initially — is quite small. There are probably several reasons for this, but one is a relative paucity of insect prey. Scorpions are not voracious feeders; they can survive long periods without food. But, given sufficient amounts of food they multiply prodigiously. As mentioned above, the striped bark scorpion has an average gestation period of eight months (similar to that of humans), with litters of 13-47 (avg. 31) young; in the wild, cannibalism by mature males accounts for significant reductions in young survival rates.

B. An introduced human-occupied structure will typically be partially illuminated, at night with artificial lighting, either in the form of exterior security lights, or indirect lighting through the dwelling’s windows. This will attract flying insects from the surrounding wilderness to the structure. In such settings, the populations of flying insects that would normally be scattered rather evenly over the surrounding woodland is, at least during the night, redistributed from the darkened portion of the forest to the illuminated structure. Besides illumination, human dwellings provide a multitude of food sources for the flying insects that the nocturnal illumination attracts. These food sources insure that the flying insects remain in the area and multiply.

C. The pinpoint sources of artificial illumination typical of human occupied dwellings typically do not illuminate the entire perimeters of the dwellings. Most such dwellings  provide only a few light sources that punctuate a sea of darkness.

These three conditions are perfect for the proliferation of striped bark scorpions.

Scorpions, being photophobic, will not forage in lighted areas unless they have no choice (as in the laboratory, where scorpions kept in fully lighted receptacles will attack, kill, and digest prey in the presence of bright lighting). Thus, an idealized model environment for the scorpion would, at the very least, contain at least one well-illuminated area, and one intensely dark area. The well-illuminated area would attract insect prey, and some of that prey would fortuitously (for the scorpion) wander into the darkened area. This model environment is complete if the darkened area includes water and suitable refugia within which the scorpion can rest while not waiting in ambush or digesting its food. By comparison, an environment that is well-illuminated throughout would not serve as a model environment for scorpions, regardless of the amount of insect prey it contained. And, of course, an environment without any nighttime artificial illumination would not be any more attractive to scorpions than the wilderness itself, which explains why farm houses in earlier times — when artificial lighting was either non-existent, weak, or of short duration each night — did not record extraordinary onslaughts of scorpions similar to those now being observed (personal experience, growing up on a 20-acre farm in rural Missouri during the 1950’s).

The structure depicted in the photographs at left was built on a large tract of undeveloped, heavily wooded land. Though a large grassy field occupies the land directly behind this structure, the field is separated from it by a thin strip of mature hardwood forest. Thick forest occupies most of the land on either side of and in front of the structure.

Except for a farm house barely visible from the back of the property line (beyond the grassy meadow), almost no other structures are nearby, and on the evening this survey was conducted no lights from off this property could be seen (including from the nearby farm house). Thus, after nightfall, the property is in essence a luminant oasis in a vast sea of darkness. Such is the state of most of the buildings that are constructed in the midst of what was previously an untamed wilderness.

It was noted on this survey that the front entrance of the structure (not shown, to preserve the client’s privacy) is illuminated with artificial lighting that brightens up the immediate entrance. This lighting, in conjunction with video monitoring cameras, enhances the security of the building by reducing the risk of surreptitious human trespass. Significant darkened areas, however, were found not only to the right and left of the entrance, but on the sides. Along the sides of the structure were several isolated, darkened alcoves. The back of the structure, which included a walled-in courtyard (fig. 200, left side of image), is lighted all night long within the courtyard itself, but no lighting is provided on the exterior courtyard wall to illuminate the landscaped area between the wall and the nearby forest.

This setting provides a near-perfect environment for attracting scorpions, and for the scorpions so attracted to multiply and flourish. Brightly lit areas, alternating with darkened areas, with darkened “corridors” on the ground, connecting the surrounding wilderness to the structure, give these animals protected routes of ingress and egress from areas of refuge (the forest, its ground litter, and the rocks and branches on the ground) to areas where abundant prey can be found (the brightly lit portions of the structure) and exploited (darkened “safe” areas near each bright light).

Population dynamics involving scorpions in such settings do not bode well for a scorpion-free spring, summer, and fall.

Under the circumstances described above, it should be expected that scorpion populations will tend to increase to significant numbers over time. Unlike most insects, which are capable of multiplying exponentially within days or weeks, it takes months for scorpions to grow to the point that they constitute an extreme infestation, but even in the initial stages they constitute a positive “pressure” on the human dwelling located there. That pressure, like water in a vessel, will exploit every seam in the vessel that is prone to leak. The seams in a human dwelling include the nooks and crannies in the exterior walls, the crevices at each wall junction and joint, the weep-holes in the masonry, holes around electrical and plumbing fixtures, and the myriad of such seams throughout the structure’s roof.

Suffice it to say that scorpions have no difficulty entering ordinary human dwellings. And though it is technically feasible to seal dwellings to the point that they are impermeable to such creatures, procedures of this sort create more problems than they solve. Well-sealed homes, being poorly ventilated, become reservoirs for unhealthy levels of volatile gases and moisture. The home building industry learned this lesson, at great expense to builders and homeowners alike, in the 1970’s, though many of those lessons seem to have been forgotten (as evidenced by the number of “authorities” recommending the sealing of homes to economize on energy losses today). Such homes tend to develop systemic infections of mold and mildew, including the toxic mold Stachybotrys chartarum (CDC, FAQ on Mold), and thus create serious health risks for their human inhabitants.

The net of this is two-fold. First, if we permit conditions in the immediate perimeters of homes to foster the development of large populations of scorpions, some of those scorpions will be lured into those dwellings, even though the dwellings do not provide a favored habitat for them. This happens for a myriad of reasons, including the scorpion’s tendency to follow an attraction trail consisting of mechanical & chemical cues produced by prey and/or potential mates.

While mechanical and chemical cues indicative of prey and mates provide strong attractants, they are subordinate to the scorpion’s natural photophobia (a dislike of light). The presence of electromagnetic radiation in the ultraviolet spectrum is detected not only by the scorpion’s eyes (e.g., the median eyes depicted in fig. 007, and the lateral eyes in fig. 006, in the first montage on this page, above), but also by photo receptors in the integument of the scorpion’s dorsal mesosoma. The latter photo receptors are thought to be so sensitive that they area able to detect the fluorescence produced by the exoskeleton’s hyaline layer in response to the minute UV radiation emanating from stars and moonlight. These faculties are capable of guiding the scorpion into the darkest shadows of its foraging environment, where it waits in ambush for insects to happen by.

On this particular survey, though conducted after dark on a moonless night, only three scorpions were observed on the exterior of the structure. Several more were observed in the deep woods nearby, mostly in conjunction with the presence of an arboreal stand of prickly pear cactus (a favorite haunt of the striped bark scorpion). Two of those on the structure exterior were in the darkest portions of the exterior wall, but remarkably near lighted areas where flying insects were present in large numbers. The third scorpion was on a partially lighted curved wall, where its integument would not have been illuminated by the artificial lighting in the distance.

Further investigatory surveys of this property are planned for the near future. From the results of these surveys, recommendations will be made to the owners of the structure regarding habitat modifications needed to produce an environment that no longer attracts or nurtures scorpions. These recommendations will include additions to the lighting on the property, with a view toward producing an unbroken fully-illuminated perimeter around the structure, through which scorpions cannot venture surreptitiously.

It is important that this lighting be controlled by dusk-to-dawn photo sensors. At this latitude dusk and dawn vary in timing widely throughout the year, which rules out the use of ordinary timers. Reliance on employees to turn exterior lighting on and off is similarly problematic. Electronically mediated dusk to dawn lighting will deny the scorpions access to nocturnal foraging zones on the building itself, and even though such areas will continue to exist, and abundant insect prey will persist in the vicinity of the lights, the scorpions will lack the access zones needed to exploit them.

In the meantime, as these changes are being evaluated and implemented, important auxiliary measures, such as applying non-toxic, non-pesticidal habitat modifiers in the form of granules and sprays are being used as washes and cleansers that wash away fecal matter and their associated pheromones, creating an environment around and inside this structure that neither nurtures nor attracts scorpions.

The granules consist of finely-granulated corn cob impregnated with a medley of aromatic essential plant oils (rosemary, cedar, cinnamon leaf, corn mint, eucalyptus citriadora, sweet bay, peppermint, and phenethyl propionate). The sprays have a base of low-viscosity food-safe mineral oil infused with various mixtures of aromatic essential plant oils. The aromatic ingredients in these products provide, at the surfaces where these products are applied, a washing action that dissolves and washes away the fecal droppings, natural odors, fragrances, pheromones, and other chemicals that are left behind by insects and other animals.

This washing and cleansing action is considered the primary function of these products.

In addition, their ingredients apparently produce a beneficial, but unintended cacophony of chemical stimuli that confuse and dull the perceptions of insects and arachnids. Most invertebrate animals, including scorpions and brown recluse spiders, are sensitive to specific natural chemicals deposited in their environments by potential mates and/or prey. They are attracted by some, repelled by others, comforted by still others. As long as the environment contains traces of these chemical deposits that can be detected and analyzed, the animals there rely on them to acquire and maintain a sense of the “state of the environment” (SOTE sensing), and all is well. Disruptors that wash away, or mask (with unrelated chemical noise), such chemical deposits make SOTE sensing impossible. Chemical noise is produced by a wide variety of natural, botanically-derived substances, as well as from aromatic household cleansers, including, for example, Pine-Sol®, a cleanser manufactured by the Clorox Company that is comprised of alkyl alcohol ethoxylates,

Individual natural essential plant oils tend to generate significant chemical noise where they are applied as cleansing agents, due to the wide array of bioactive chemicals they contain. For example, assays of the constituents isolated in specimens of Texas cedar oil (from Juniperus mexicana) have identified, at minimum, 10 distinct bioactive compounds. Lemon eucalyptus oil (from Corymbia citriadora) has at least 16; cinnamon leaf oil (from the foliage of Cinnamomum verum) has 34; rosemary oil (from leaves and stems of Rosmarinus officinalis) has 50; and corn mint oil (from Mentha arvensis) has 67. Many of these bioactive compounds are unique to the specific oil involved; some are found in all of them, though often in combinations unique to the source botanical; yet others are in two or more, but not in all.

Applying aromatic granules with a hand dispenser, and aromatic liquid sprays with an hand-operated spray nozzle, creates washed bands of naturally derived, non-toxic, matter around the exterior perimeter of a structure, and on walls and carpeted areas inside a structure. These materials wash those surfaces, making them attractant neutral. The fragrances produced by these materials are not normally objectionable to humans outdoors, even for extended periods of time. Indoors, however, the use of strong fragrances, even if generally appreciated by most people, wears after a short while. Thus low-odor formulas are more suitable for use in a structure’s interior without.

Using these products creates a cleaned zone free of dirt, grime, objectionable odor, and objectionable visible detritus such as webbing and arthropod feces. For arthropods that enter that zone, it is perceived as a washed band that does not attract or repel them. It also creates a zone of chemical noise within which the ordinary chemical cues left behind by insects, arachnids, mice, rats, and reptiles, are masked. The effect is not pesticidal or repellent to scorpions, brown recluse spiders, or to other organisms, nor does it serve to mitigate such pests; it merely creates a limited area within which arthropods are neither attracted nor nurtured by the ordinary repertoire of chemical cues they commonly use to locate and differentiate prey and mates, and to avoid predation from known enemies. As such, it dovetails perfectly with other elements of a well-developed PestAvoidance program, most of which involve mechanical habitat modifications.

The consequence of this effect differs with the specific organism involved. For scorpions the effect is particularly significant, as they depend on chemosensory stimulation, from the thousands of peg sensilla that adorn the featherlike pecten appendages (figs. 014, 015, 016, 105, & 110, above) on the undersides of their bodies, to find prey and mates, and to avoid predators. The peg sensilla are used to “sniff” the substrate on which scorpions travel.

A recent study (Gaffin et al., 2004) found that scorpions conduct regular chemical “sniffs” of the environment by lowering their pectens until they make contact with the substrate below; they then maintain contact for a short but measurable period of time, lowering the pecten for approx. 0.20 sec., followed by approx. 0.07 second retraction, with actual substrate contact lasting, at most, 0.033 seconds. Besides the pecten “sniff” the investigators also observed scorpions dragging their pectines for a longer period of time, either just above or directly on the substrate, before retracting them.

The cited study was conducted to determine if the peg sensilla populating each pectine consisted of arrays of functionally different kinds of sensilla, each capable of detecting only a narrow range of specialty chemical stimulants, or, instead, of functionally identical sensilla, each capable of detecting a broad range of generalized chemical stimuli. The data collected in the study suggested they are functionally identical. In other words, the scorpion may not possess specialized sensilla that only detect the presence of prey, others to detect mating pheromones, and others to detect predators (though a later study (Gaffin, 2010) did confirm that different waveforms, identified in that study as types A1, A2, and B, emanate from the chemosensory cells of scorpion peg sensilla). One conclusion from this is that, within an environment rich in chemical “noise,” the scorpion’s ability to find and track the less potent chemical cues commonly used to home in on prey and prospective mates, and to avoid predators, is inhibited, severely limited, or entirely neutralized.

Like other ambushers in the arthropoda (e.g., recluse spiders in the Sicariidae family), scorpions appear to spend much of their foraging and resting time in a state of quiescence analogous to suspended animation. In this state, their metabolic rates drop, along with heart rates and respiration. Transition from this state to one of activity, with all of the scorpion’s faculties at or near full functionality, occurs within a relatively short time span in response to introduced mechanical or chemical stimuli. In an environment with low ambient levels of such stimuli, such transitions would occur more efficiently than in environments rich in chemical or mechanical “noise,” contributing — one would surmise — to a healthier, longer living scorpion.

Circumstantial evidence indicates the number of scorpions found foraging and taking refuge in environments rich in the kinds of chemical “noise” produced by essential plant oils is severely reduced. Although those used in the granular and spray formulas tested for this article were chosen for their cleansing faculties, they are known to effectively produce chemical noise as well. If, as hypothesized, scorpions actively conserve the functionality of their chemosensory pectines by selecting foraging zones and refugia where their pectines are fully operational, i.e., where their ability to detect minute chemical cues deposited by prey, mates, and predators is enhanced, vs. locations rich in such chemical noise — where such abilities are inhibited — would not be attractive or nurturing to scorpions. Thus their presence in such locations would be significantly reduced.

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• Shelley, Rowland M., and W. David Sissom, 1995. Distributions of the scorpions Centruroides vittatus (Say), and Centruroides hentzi (Banks) in the United States and Mexico (Scorpiones, Buthidae). J. Arachnology 23:100-110.
• Sissom, William David, 1980. Life histories of two North American scorpions: Centruroides vittatus Say (Buthidae) and Vaejovis bilineatus Pocock (Vaejovidae). Master’s Thesis, Texas Tech University.
• Whitmore, Donald H., et al., 1985. Scorpion Cold Hardiness. Phyusiol. Zool. 58(5);526-537.
• Yamashita, Tsunemi, 2004. Surface activity, biomass, and phenology of the striped bark scorpion, Centruroides vittatus (Buthidae) in Arkansas, USA. Euscorpius, 2004, No. 17.

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