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Activity Trends and Movement Distances in the Arizona BarkScorpion (Scorpiones: Buthidae)Author(s): Christopher Stephen Bibbs, Sarah Elizabeth Bengston, and Dawn HeatherGougeSource: Environmental Entomology, 43(6):1613-1620. 2014.Published By: Entomological Society of AmericaURL: http://www.bioone.org/doi/full/10.1603/EN14148

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BEHAVIOR

Activity Trends and Movement Distances in the Arizona Bark Scorpion(Scorpiones: Buthidae)

CHRISTOPHER STEPHEN BIBBS,1,2 SARAH ELIZABETH BENGSTON,3 AND DAWN HEATHER GOUGE4

Environ. Entomol. 43(6): 1613Ð1620 (2014); DOI: http://dx.doi.org/10.1603/EN14148

ABSTRACT The bark scorpion,Centruroides sculpturatusEwing, is a nocturnal, cryptic, nonburrowing,mobile species that iscommoninurban landscapes spanning thedesert southwest.Barkscorpionsareoftenfound in dense localized populations in cities, but the question of whether this is because the species ismetabolically movement limited or choose to aggregate has not been addressed. Field observations leadus to believe that the scorpions move very little. Their ability to move is tested here. A circular pacing ringwasconstructed toobserve thedistance individualscouldmove in2hunderbothdarkand lightconditions.Observations under light motivate the arthropods to move, and signiÞcantly greater distances wereobserved in light trials, the maximum travel distance being 104.37 m, while the maximum distance in darktrials was 14.63 m. To monitor movement in the Þeld, telemetry tags were used to mark female and malescorpions over 21 d during which relocation distances were recorded daily. Additionally, 12-h and 6-hovernight observational periods took place during which, scorpion movements were recorded hourly.Overall, it was found that scorpions moved signiÞcantly more in the pacing ring than in the Þeld, indicatingthat Þeld individuals are not moving at their maximum potential. Movement limitation does not explaintheir distribution pattern. In both the pacing ring and Þeld, gender and pregnancy status had signiÞcantinßuenceondistancesmoved.Weconclude thatC. sculpturatus is capableofmuchgreatermovement thanis typically observed in the Þeld.

RESUMEN El escorpion de bark, “Centruiroides Sculpturatus” Ewing es un escorpion nocturno (denoche). Es crõptico, sin escavar, y un especie movil que es comun en los paisajes urbanos que existenen el desierto del suroeste. Se encuentran los escorpiones de bark en las ciudades locales y compactasy que tienen altas populaciones. La pregunta es: ÀPor que vienen los escorpiones a estos lugares? ÀEspor que el especie es del movimiento metabolico o es por que los escorpiones escogan agregarse? Estapregunta todavõa no tiene una respuesta. Las observaciones del campo nos dirigen creer que losescorpiones mueven muy poco. Su abilidad moverse se prueba aquõ. Un anillo circular de velocidadfue construido para observer la distancia que los escorpiones pueden mover en dos horas seguncondiciones de la luz y de la oscuridad. Las observaciones debajo la luz les hacen a los insectos mover,y es una distancia bastante mas larga que en las condiciones de la oscuridad. La distancia maxima quemovieron debajo la luz fue 104.37 metros, mientras la distancia maxima debajo la obsuridad fue 14.63metros. Para controlar el movimiento en el campo, marcas de telemetrõa fueron usadas para distinguirentre los escorpiones femeninos y los masculinos durante los 21 dõas en que las distancias dereubicacion fueron recordados diaramente. Tambien, las observaciones de las 12 horas y las 6 horaspor noche se realizaron mientras que los moviemientos de los escorpiones fueron recordados cadahora. Segun todo, se encuentra que los escorpiones movieron signiÞcativamente mas en el anillo develocidad que en el campo. Este nos indica que los insectos del campo no se mueven tanto que tenganla capacidad mover. El lõmite del movimiento no explica su manera de distribuirse. En los dos casosdel campo y del anillo de velocidad, el genero y el estado de embarazo tuvieron una inßuenciaimportante en las distancias que movieron. Terminamos que el escorpion “Centruioides Sculpturatus”Ewing es capaz de moverse mucho mas que fue observado en el campo.

KEY WORDS Centruroides, movement, behavior, urban habitat, built environment

Centruroides sculpturatus Ewing, the Arizona barkscorpion, is a generalist predator and native to thedesert southwest (Ewing 1928; Stahnke 1956, 1971;

Hadley and Williams 1968; Ennik 1972; Crawford andKrehoff 1975). This species was synonymized withCentruroides exilicauda by Williams (1980), and re-

1 Entomology & Insect Science Program, College of Agricultureand Life Sciences, University of Arizona, 1140 E. South Campus Dr.,Forbes 410, Tucson, AZ 85721.

2 Corresponding author, e-mail: csbibbs@outlook.com.

3 Department of Ecology & Evolutionary Biology, University ofArizona, P.O. Box 210088, Tucson, AZ 85721-0088.

4 Department of Entomology, University of Arizona, Tucson, AZ85721.

0046-225X/14/1613Ð1620$04.00/0 � 2014 Entomological Society of America

mained that way until molecular data and venom char-acterization upheldC. sculpturatus as a distinct speciesin 2004 (Valdez-Cruz et al. 2004). Like other barkscorpions, C. sculpturatus is cryptic in its native hab-itat, does not construct its own burrows, and wandersto Þnd resources (Stahnke 1966, 1971; Hadley andWilliams 1968). Although desert adapted (Hadley1974, Polis 1990), the Arizona bark scorpion is pref-erential of riparian habitats because water availabilityis one of its limiting factors (Hadley and Williams 1968,Hadley 1971, Polis 1990, Carlson and Rowe 2009). Dueto a combination of these preferences and deliberatesearching for water to drink (Hadley 1971), the Ari-zona bark scorpion has become an unexpectedly com-mon concern in urban desert habitats (Smith 1982,Boyer et al. 2001, Gouge and Snyder 2005). Thus, lowdesert communities may report signiÞcant problems,as this pest is a medically signiÞcant scorpion in theUnited States (Stahnke 1966, Keegan 1980).C. sculpturatus use plants, rocks, debris, cement

walls, storage buildings, and human items as harboragesites (Crawford and Krehoff 1975, Polis 1990, Bibbs etal. 2014) often living in proximity to humans. Moreimportantly, concern over a venomous pest has causedresidents and property managers to resort to broad-spectrum pesticide applications monthly or as often asevery 2 wk, which bring additional concerns abouthuman health impacts due to pesticide exposure. Ad-ditionally, pesticides fail to effectively control scorpi-ons (Smith 1982, Roberts and Karr 2013, Trunnelle etal. 2014). Without understanding how this organismbehaves in an urban setting, possible solutions such ashabitat modiÞcation, exclusion methods, and othernonchemical controls cannot be realized. Bibbs et al.(2014) describe overall preference in refuge type, aswell as factors that predict speciÞc preferences; how-ever, many unknowns still prohibit effective popula-tion management.

One unknown concerns the movement potential ofC. sculpturatus. Scorpions, broadly, seem to have poordispersal ability (Yamashita and Polis 1995, Bryson etal. 2013). Yamashita and Polis (1995) describe densebut localized populations of C. sculpturatus; in acityscape this appears to be even more evident(D.H.G., unpublished data), but the question ofwhether this is because the species is metabolicallymovement limited or that they choose to aggregate hasnot been addressed. To date, the maximum movementpotential is not discussed in any references addressingthis species. Field observations lead us to believe thatthe scorpions move very little, unless disturbed,and then they appear to be capable of signiÞcantrelocation. Observations also indicate that C. sculptu-ratus is mobile, and capable of relocating to varyingtypes of refuges and wandering to Þnd resources.Related work on C. vittatus tested sprinting speedsobserved under lab conditions (Shaffer and Formano-wicz 1996), but provided no measure of how muchdistance was voluntarily covered without initiating anexhaustive state. This study investigates whether C.sculpturatus is physically capable of dispersing beyond

the tight local populations they are found in aroundstructures.

Materials and Methods

Scorpions used in the trials were found using UVlight ßuorescence and hand collected using 30.48 cm(12 in) forceps at night in southeastern Arizona citiesreported to have incidence of bark scorpion activity.These principally include Phoenix, Chandler, Mesa,Tucson, and Vail. All scorpions were kept communallyin a ventilated plastic snap lid container containing asingle strip of corrugated cardboard harborage and asponge wetted with water daily. Scorpions were of-fered house crickets (Acheta domesticus L.) biweekly.Test trials of any kind were restricted to start dateswithin 2 d of the most recent feeding. This was todecrease the effect of hunger on the behavioral assaysand to screen for individuals that were unwilling tofeed and therefore deemed unable to participate inthe trial. Scorpions used in trials were then randomlyselected from containers.Distance Assays. The experimental arena was cre-

ated (Fig. 1) after testing a series of preliminary con-Þgurations; a circular pacing track proved to be thebest experimental design. Original designs included arectangular track. But the corners of the track becameinhibitive, as scorpions would often stop all movementfor several hours upon reaching a corner. The dropbox used in the Þnal assay design, see Fig. 1, wasselected because an entirely clear drop box resulted inpanic (indicated by frantic, erratic movement orstruggling) throughout acclimation periods and ledthe scorpions to exhaustion with no movement oncetrials began. This was possibly the result of no refugein the entire conÞguration. The dark contrast of thebox remedied the continuous erratic movement ob-served during acclimation and allowed data to be re-corded. Tape was used to mark the clear Plexiglasshields. The design of the arena limits airßow; without

Fig. 1. Movement potential assessment arena. Visible arethe acclimation drop box, the marked Plexiglas shields usedto control scorpion access, and the circular pacing track thescorpions traveled during timed intervals. (Online Þgure incolor.)

1614 ENVIRONMENTAL ENTOMOLOGY Vol. 43, no. 6

it, scorpions were randomly startled or would stopmoving once reaching certain sections of the circuit.Inspection found that even the act of the observerbreathing near the track when the arena was notadequately sealed resulted in the scorpions being dis-turbed, forfeiting the continuity of the data. Sealingthe track thoroughly allowed the scorpions to proceedwhile mitigating disturbance from observation. Fordark trials, red overhead lighting was selected amongthe choices of dimly powered white light, total dark-ness, red light, and UV black light. For dim white light,the observed behavior did not change from the lighttrials. For total darkness, it was impossible to accu-rately record observations and movement data giventhe resources available. For UV black light, the scor-pions still showed signs of stress, occasionally dartingswiftly as if to escape a stimulus. The red lightingallowed enough visibility for observation and record-ing without also provoking the darting behavior seenwith the UV black light.

Scorpion movement distances were recorded usinga circular pacing track. Clear vinyl tubing of 2.54 cm(1 in) inner diameter was cut into 30.48-cm (1 foot)-long sections and then halved lengthwise, creating30.48-cm (1 foot)-long clear vinyl half-pipes. This pip-ing was anchored to white foam particle board creat-ing a 193.04-cm circular pacing track; low temperaturehot glue (0440, Ad Tech, Oldsmar, FL) was used toseal the pipe to the particle board base and the entirecircuit was closed off against external airßow. A T-junction using a 10.16-cm span of pipe and an addi-tional 20.32-cm section was created, forming a leadinto the track. At the end of the junction was a plastichinged lid box for dropping in scorpions (Fig. 1).Where the T-junction met the track circuit, a sectionof pipe at both ends of the T-junction was connectedto the circuit and a section of the pipe leading to thedrop box was cut out to allow the addition of a re-movable Plexiglas shield. The shields were markedwith two vertical strips of tape. When shields were notin use, the slits in the piping were sealed using clearplastic cling wrap (Sku: 2113027001, Safeway Inc,Pleasanton, CA) to maintain the clear design of thecircuit.

All testing took place in a constant temperatureroom maintained at 25�C and 8Ð12% relative humidity(RH) with no windows and all external light entry,such as under doorways, blocked using opaque blackplastic. Scorpions were labeled with the trial numberof the current test using plastic bee tag numbers(#1172, BioQuip, Rancho Dominguez, CA), mountedto the dorsum, using gel super glue (IDH#234790,Rocky Hill, CT). Immediately after each trial the par-ticipating scorpions were dried and frozen, weighedand measured laterally from anterior edge of the car-apace to the basal connection of the metasoma inmillimeters. Plexiglas shields were set in the two lat-eral sides of the four inch T-junction section linkingthe circular track, but not in the path leading to thedrop point. The scorpion was then admitted to thedrop box, the box closed, and the entire set up left inthe testing conditions of the trial for an acclimation

period of 24 h starting at 0800 hours of the day beforetesting. At the start of the trial at 0800 hours thefollowing day, the shields blocking the circular trackwere lifted, allowing the scorpion to enter the circuit.A shield closing the entry path was then dropped anda timer started for a 2-h interval as soon as the scorpionentered the track of its own accord. Lap revolutionswere recorded along with observations on styles ofmovement as they differed between males, females,and visibly pregnant females. Males and females wereidentiÞed based on metasomal segment lengths (in-determinate individuals were not included, but it ispossible that juveniles were accidentally included asfemales). Males were identiÞed according to longerindividual metasoma segments that result in beingunable to coil the metasoma at rest. Pregnant femalesfor the purposes of this study were those whose ova-ries harbored visible embryos by viewing through theventral cuticle. Two sets of 50 repetition trials wererecorded, using one scorpion for a 2-h interval eachtime. The Þrst set involved the lab room being well litwith the existing overhead ßuorescent light Þxtures.The second set was a dark room design with all lightsand light sources turned off or blocked with the ex-ception of a single 60 watt equivalent red ßuorescentbulb centered over the experiment table. In betweeneach usage, regardless of trial type, the track tubingwas separated from the base and the board was wipeddown with 70% ethanol (to remove uric acid excre-tions) and allowed to air dry before reassembling. Alldistances recorded between the two trial types werethen summarized for mean, maximum, and minimumdistances. Analysis of variance was used to determineif gender and pregnancy held signiÞcance in themovement outcomes. A MannÐWhitney test was usedto evaluate disparity between the light and dark trials.All statistical analyses were carried out at a 5% level ofprobability (� � 0.05).RadioTelemetry. Twenty telemetry tags (Biotrack

PicoPIP Ag337 radio transmitter, LoTek, Ontario,Canada) were calibrated to individual frequencychannels ranging from 164.048 MHz to 164.978 MHzand labeled using plastic bee tag numbers (#1172,BioQuip, Rancho Dominguez, CA) with the corre-sponding channel. The frequency channels werestored in the program memory of a telemetry receiver(1 MHz Biotracker, LoTek, Ontario, Canada) Þttedwith an antenna (Yagi folding 3-element antenna,LoTek, Ontario, Canada) for directionalized recep-tion boost. All tags were constructed to a mass of 0.29 g.The tag design included a 7-cm antenna, weatherresistant coating, 13-millisecond pulse width, andemission of 28 pulses per minute. Scorpions for taggingwere found by scanning the Þeld site at night with UVblacklight and grasping them with 30.48-cm (12 in)forceps for placement into an individual container.The tags were mounted at this time to the dorsum of20 C. sculpturatus, 10 females and 10 males, using gelsuper glue (IDH#234790, Rocky Hill, CT). Pleasenote, it was impossible in the dark to be absolutelycertain of sexual maturity or sex of scorpions collectedfrom the Þeld, tagged and released. Each scorpion was

December 2014 BIBBS ET AL.: MOBILITY TRENDS IN THE ARIZONA BARK SCORPION 1615

returned to its point of discovery immediately afterthe telemetry tag was securely mounted (the processtaking 2Ð3 min).

The site selected for monitoring bordered an ele-mentary school campus in Mesa, a city on the east sideof thePhoenixvalleyarea.Coordinateswere33�27�41�N, 111� 45�47� W, centered on an �100-m stretch ofhollow, 15.24 cm � 20.32 cm � 40.64 cm (6 in � 8 in �16 in) normal-weight cinderblock, capped cementwall. The north face met a stand of ornamental andfruiting trees. The south face of the same wall formedthe perimeter wall of the 25, 211-square meter campus.The last known location of each scorpion per day wasmarked with colored ßags annotated with the corre-sponding frequency of the tag used at that location,henceforth indicative of that individual. Using thereceiver, scorpions were located daily at midday whenmovement was least likely. Each subsequent locationwas marked with a different colored ßag to indicateconsecutive day locations.

First data recordings began on 1 August 2013 andconcluded 21 August 2013. The moon was in the thirdquarter (23.4% illumination) on August Þrst and wasfull August 21st (99.7% illumination). Absolute dis-tances between consecutive days harborage were re-corded in a straight line from one marker to the next.Additional tracking distances were recorded duringone 12-h period and two 6-h periods starting at 1900hours and repeated hourly to observe nighttime move-ment activity. Observations were recorded and re-lated to the daily distance readings. Tracking con-cluded 21 d after tagging in approximation of thebattery life deadline. Distance information was thensummarized for mean, maximum, and minimum forthe daily recordings and each hourly night time track-ing stint. A general additive model (GAM) was usedto explore whether individual preference, estimated

gender, pregnancy status, temperatures, humidity,and wind were predictive of the movement outcomes.Linear regression between both 6-h overnight inter-vals was used to check for patterns of movement at-tributable to 24-h rhythms. A MannÐWhitney U testwasperformed to seehowtheÞeldmovementdifferedfrom the lab recorded movements. All statistical anal-yses were carried out at � � 0.05 signiÞcance levelusing “R” statistical software, v2.14.2 with Tinn-R Ed-itor graphic user interface. Observational notes re-garding trends in activity throughout a night are alsoreported.

Results

Distance Assays. During the light trials, the mini-mum travel distance was 19.74 m; the median traveldistancewas70.38m; themaximumtraveldistancewas104.37 m; the mean travel distance was 70.12 m (Fig.2). One-way ANOVA supported that gender (F �12.95, df � 1, P � 0.001) and pregnancy (F � 11.75,df � 2, P � 0.001) affected the travel distance. Maleson average traveled farther than females at a meanvalue of 74 m. Females that were not pregnant aver-aged lower travel distances of 63 m. Females that werepregnant averaged the lowest travel distances of 47 m.During the dark trials, the minimum travel distancewas 0 m; the median travel distance was 0.55 m; themaximum travel distance was 14.63 m; the mean traveldistance was 2.15 m (Fig. 3a and b). The data did notfollow a normal distribution, so a MannÐWhitney Utest was performed to determine that gender (P �0.337) had no discernible effect on the recordedmovement distances. A KruskalÐWallis test was usedto determine if pregnancy status affected distance andwas found to have no signiÞcance (P� 0.465). Malestraveled an average of 2.80 m. Females that were not

Fig. 2. Histogram visualizing the spread of scorpion movement across 50 light trials, each trial recording distances for onescorpion each. X-axis shows total travel distance broken into categories of 5-m increments. Y-axis shows the number ofscorpions that traveled a distance that falls into each range.

1616 ENVIRONMENTAL ENTOMOLOGY Vol. 43, no. 6

pregnant traveled an average of 1.50 m. Females thatwere pregnant traveled an average of 3.10 m. A MannÐWhitney U test indicated that scorpion travel dis-tances varied signiÞcantly between light trials anddark trials (U � 2500, z � 8.617, P � 0.001).RadioTelemetry. The daily recorded Þeld data are

summarized as a mean relocation distance of 1.25 m,a minimum distance of 0 m, and a maximum distanceof 31.57 m. A general additive model on the dailyrelocation measurements indicated that individualpreference (P� 0.001), high temperature (P� 0.001),low temperature (P � 0.001), high humidity (P �0.001), low humidity (P � 0.1), maximum windspeed (P� 0.001), and average wind speed (P� 0.1)held no predictive power over scorpion movementdistances, but gender (P � 0.010) and to a lesserextent pregnancy status (P � 0.050) did. A linegraph for this daily data (Fig. 4) demonstrates whatseem to be erratic bursts of relocation. The 12-hovernight tracking stint where distances were re-corded hourly is summarized as a mean travel dis-tance of 0.425 m, a minimum distance of 0 m, and amaximum distance of 16.46 m. A line graph of thisinterval (Fig. 5) indicates this movement was pri-marily from one individual. A GAM of these dataindicated that individual preference (P �� 0.001),gender (P �� 0.001), hourly temperature (P ��0.001), hourly humidity (P �� 0.001), and hourly

wind speed (P �� 0.001) were not predictive of thedistances traveled. It should be noted that the outliervisible in the line graph (Fig. 5) is a male. In a pairedt-test between the daily data set and the 12-h data set,movement rate per hour was assessed by apportioningthe data to separate treatments. The results suggest thedaily period reßected more movement than the 12-hinterval with an hourly period (P � 0.041, T � 2.21).

For the Þrst 6-h overnight interval on 20 August2013 where distances were recorded hourly, move-ment is summarized as a mean of 0.29 m, a minimumof 0 m, and a maximum of 8.53 m. For the second 6-hovernight interval on 21 August 2013 where distanceswere recorded hourly, movement is summarized as amean of 0.188 m, a minimum distance of 0 m, and amaximum distance of 8.53 m. General additive modelsfor both of these 6-h intervals also indicated that in-dividual preference (P�� 0.001), gender (P�� 0.001),hourly temperature (P �� 0.001), hourly humidity(P �� 0.001), and hourly wind speed (P �� 0.001)were not predictive of the distances traveled. A linearregression between the two 6-h data sets suggeststhere was no consistency between the movement datasets over a 24-h period given the time scale of the data(P � 0.593, R2 � 0.0029).

Comparison of the in-lab movement trials and thetelemetry Þeld data using a MannÐWhitney U testindicated that scorpion travel distances varied signif-

Fig. 3. Histogram visualizing the spread of scorpion movement across 50 dark trials, each trial recording distances for onescorpion each. (a) X-axis shows total travel distance broken into categories of 0.5-m increments. Y-axis shows the numberof scorpions that traveled a distance that falls into each range. (b) Distribution of scorpion movement within the 0Ð0.5 mcategory with categories reassigned at 0.05-m increments. Axis labels are shared with overall graph. (Online Þgure in color.)

December 2014 BIBBS ET AL.: MOBILITY TRENDS IN THE ARIZONA BARK SCORPION 1617

icantly between the lab and the Þeld (U � 900, z �6.25543, 2-tailed P � 3.96416e10).

Discussion

Bark scorpion distances recorded in circular pacingtrack tests were much greater than expected. Thedisparity between the distances traveled in continu-ous light versus dark showed that the scorpions weremotivated to move; it is assumed they are seekingharborage. However, scorpion movement did not ap-pear tobe thatofpanic. Inunrecorded trialsduring theoptimization of the experimental set up, stressed scor-pions would dart swiftly in a dash. The design andacclimation interval were altered to ensure that scor-pions would not be in a state of stress. That kind ofbehavior was not observed in any of the trials re-corded.

The Þnding that males traveled on average fartherthan females is consistent with the idea that malescorpions maintain higher activity levels as theysearch for mates (Steinmetz et al. 2004). In light trials,males maintained a more elevated walking stance.

Movement patterns consisted of short, quick burstsfollowed by brief rest intervals of about 2 min. Maleswere also highly exploratory, pinching at the experi-mental set up, pushing on gaps, and attempting towedge themselves under the Plexiglas shields. Fe-males kept a lower walking stance with a shallow gapbetween the venter and substrate. Their movementpattern had fairly consistent stride, but they seemednot to move as quickly as the males. This was temperedby females tending to walk fairly continuously and nottaking many rest periods. When the females did rest,it was often for �20 min. They were also not as ex-ploratory as males, ignoring continuity differences inthe experimental apparatus and not attempting tomove the Plexiglas. Additionally, scorpions of differ-ent pregnancy status also differed. For females withinternal brood, these observations were consistent,but rest periods were observed more often than withnonpregnant females. By contrast, in the dark trialsthere was relatively little movement. All scorpionswere still active, despite not traveling around the ring.Frequent observations of grooming, hunting postures,and elevating the venter from the substrate indicated

Fig. 4. Line graph representing all scorpion movement recorded at a daily time interval for all tagged scorpions; 21-dtracking period. X-axis represents the tracking day. Y-axis represents distance traveled in meters. Legend indicates telemetrytag channel number; 1Ð10 are females, and 11Ð20 are males. (Online Þgure in color.)

Fig. 5. Line graph representing all scorpion movement recorded at a 12-h overnight interval for all tagged scorpions;interval from 1900 to 0700 hours the next morning. X-axis represent the tracking hour. Y-axis represents distance traveledin meters. Legend indicates telemetry tag channel number; 1Ð10 are females, and 11Ð20 are males. (Online Þgure in color.)

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wakefulness. Behavioral activities where not method-ically recorded during these tests, but future studiescould track the amounts of time males, gravid females,and nongravid females spend walking, resting, groom-ing, etc.

In the Þeld, we expected a correlation with humid-ity, temperature, or both, given that water seeking isso important in the biology of C. sculpturatus.Whilethis was not found, the GAM did indicate gender andpregnancy status as predictors of movement distance.This could be due to gender-based behavioral differ-ences, like mate seeking on the part of the male.However, inspection of the line graph shows that fe-malesweremoreconsistent in theirmovement,havingrelatively regular relocation in 3-d spurts. Males hadrelatively low but frequent movement, with occa-sional bursts, and in the case of one individual anextended high level of movement over several days. Itis reportedbySteinmetzet al. (2004) thatCentruroidesmales change their behavior depending on the pres-ence of females. Before being near females, males haderratic bursts of activity. After being exposed to evi-dence of females, the males would change to short,controlled, search-oriented movement. What Figs. 4and 5 may be showing is that the male group beingtracked is concentrating its presence in a small area,thus not showing much obvious movement. The out-lier scorpion may be an example of the erratic search-ing behavior. Steinmetz et al. (2004) also note thatmales do not demonstrate this change in behaviorthrough all seasons. It would be beneÞcial to follow upwith another tracking effort during an earlier part ofsummer, before the onset of seasonal rains in thedesert southwest (and triggering of mate-seeking be-havior).

Because the daily period yielded more variabilityand between the two 6-h intervals no consistent pat-tern could be seen, it must be stressed that the trackingresults did not address activity outside of the particularinstances recorded. Additionally, in lab assessments,scorpions were active without necessarily moving tonew locations. During the night time observations,scorpions were found grooming, poised for prey cap-ture, or otherwise patrolling tight areas that were notlarge enough to lead the scorpion a reasonable mea-suring distance away from its last position. During Þeldtracking intervals the following pattern of activity wasobserved: scorpionsbeganactivityat theonsetofdusk;at the tracking location and dates this was approxi-mately starting at 1900 hours. During the 12-h trackinginterval, active wakefulness was observed for approx-imately the Þrst 4 h. By midnight, scorpions no longerappeared to be grooming or in ready postures. A pe-riod of low activity lasted for approximately 3 h; after0300 hours, the scorpions became easily agitated byminimal disturbance and began retreating to nearbyharborage. During the two 6-h tracking intervals (both1900Ð0100 hours), the same activity trend was ob-served. These observations match up with the Þndingsof Crawford and Krehoff (1975) who explored activitypatterns of scorpions, including C. sculpturatus. Theirexperiments indicated that C. sculpturatus were ini-

tially active with the onset of darkness, followed byinactive periods later on.

Annotations were also recorded on unmarked scor-pion activity during night time observations. Duringboth of the 6-h intervals, a dust storm and a full moonoccurred; these may have been inßuential events af-fecting movement data. Despite the fact that bothwell-lit nights and weather phenomena are reportedas deterrents to scorpion activity (Hadley and Wil-liams 1968), 70 unmarked scorpions were observedin each 6-h interval moving outside of harborage. Scor-pions near to irrigation sources ignored the moonlightand weather to drink standing water. These otherwiseunfavorable conditions may not function as a strongdeterrent to activity in the urban landscape, particu-larly if a water source is available. It was also moreusual to observe scorpions (tagged or untagged)within several centimeters of at least one other scor-pion. Although C. sculpturatus can survive as and issometimes considered a solitary organism, toleranceto conspeciÞcs leads scorpions living in dense popu-lations even outside of winter time, when they areknown to gather together in hibernacula.

The contrast of how far scorpions were capable ofmoving in the lab compared with how far they actuallymoved in the Þeld supports the theory that C. sculp-turatus is not found within densely populated pocketsstrictly because they are movement limited. Thetracked scorpions did not have need to relocate out-side of the proximal resources, as the tracking sitecontained ample harborage, insect prey, and a regularwater source. If the Arizona bark scorpion was moti-vated to relocate due to water source or harborageneeds, it is suggested that they are more than capableof moving to habitation sites farther than we assumedbased on previous literature (Hadley and Williams1968). Animals with low metabolic rates are not ex-clusively poor dispersers. The Atlantic blue crab, Cal-linectes sapidus, succeeds at necessary incidents ofdispersal due to efÞciency in locomotor activitiesrather than having higher oxygen uptake or a specialmechanism of dispersal (Booth and McMahon 1992).An important consideration to make is how often C.sculpturatus may need to relocate in an urbanizedlandscape. Cityscapes are heavily disturbed andevents such as construction, landscaping, or ßooding(due to poor water retention on land with pavedsurface) may all result in temporarily migrant popu-lations ofC. sculpturatus.The argument of low vagilitymight lead one to consider that movement across alandscape is multigenerational, as a population mayshift with a new generation spreading out further froman epicenter (Yamashita and Polis 1995, Bryson et al.2013). However, a disturbed population of C. sculp-turatus is certainly capable of dispersing further intoan urban landscape to Þnd resources. This may resultin relatively mobile populations, rather than just in-dividuals. Given the multiyear life span of scorpions(Polis 1990), this is important to consider as we modifyhabitats around and within the built environment.

December 2014 BIBBS ET AL.: MOBILITY TRENDS IN THE ARIZONA BARK SCORPION 1619

Acknowledgments

Jude McNally is thanked for his representation of thisprojectÕs interests to the funding associates allied with RareDisease Therapeutics, Inc. in the southwestern region of theUnited States. Information leading to scorpion acquisitionwas provided by the Tucson Poison and Drug InformationCenter courtesy of afÞliates Keith Boesen, Jude McNally, andDan Massey. We thank Mike Ellsworth for Spanish transla-tion of the abstract. The funding for this project was providedby Rare Disease Therapeutics, Inc.

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Received 26 May 2014; accepted 24 September 2014.

1620 ENVIRONMENTAL ENTOMOLOGY Vol. 43, no. 6