The study examined the home range of the bark scorpion Centruroides vittatus in Laredo, Texas using mark-recapture methods from 2009-2010. A total of 31 scorpions were collected and marked. The minimum convex polygon and local convex hull methods were used to estimate home range sizes. Males were found to have significantly larger home ranges and travel greater distances than females. Recapture rates were around 50% overall. The study provided a basis for further examining factors that influence scorpion home range sizes and patterns of microhabitat use.

1. By: Jose Luis Chapa

2.  Centruroides vittatus is nocturnal and generally
finds refuge during the day under bark,
beneath vegetation, in holes in the ground
(Polis 1990).
 C.vittatus and other bark scorpions rarely dig
their own burrows (Polis 1990).
 C.vittatus do not emerge from their refuge
every night, but when they do they actively stalk
their prey (Hadley and Williams 1968)

3.  The study was conducted on the campus of
Texas A&M International, Laredo,TX.
 The habitat of the study site is described as
thorny brush (Blair 1950) or chaparral.
 An area of approximately 0.3 hectares was
flagged.
 Used previously for C.vittatus studies
(McReynolds 2004, 2008)

4. © 2010 Google maps – Map data © 2010 Europa Technologies , Geocentre Consulting, INEGI
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100 m

6.  Microhabitat use can be associated with
seasonal changes in prey availability and
predation risk.
 Microhabitats can serve multiple functions for
C.vittatus, but a particular habitat can be
preferred for a certain function such as refuge,
foraging, or feeding.
 Black brush (Acacia rigidula)

9.  Burt (1943) defined the home range as the area
used by the individual to carry out daily
activities like foraging, mating, and caring for
young.
 The size of the home range may vary with sex
or other factors and different individuals may
have overlapping home ranges (Burt 1943).
 The home range may change during the life of
the individual;essentially by abandoning one
home range for another (Burt 1943)

10.  Observed surface activities of North American
scorpions in relation to feeding.
 Differences in foraging behavior between
Vejovidae and Buthidae.
 Vejovidae would assume a stationary position
around their burrow.
 Buthidae would actively forage, moving
continously.

11.  Area seemed to be limited in scope and a
similar range was covered by the same
scorpion each night of activity.
 These observations suggested the likelihood of
home ranges in scorpions, even non-burrowing
forms.

12.  Conducted a study on the home range of the
desert scorpion Smeringus mesaensis (formerly
Paruroctonus).
 Home range was circular with older, and larger,
scorpions occupying more space than younger
ones.
 Possible factors affecting home range included
prey distribution, energy requirements, and risk
of predation.

13.  Study was conducted
from Feb. 2009 to Feb
2010.
 Observations began
at 20:30 and ended
at 00:30 that night.
 UV lamps were used
to locate scorpions.

14.  Observations began by selecting one flagged
area to search.
 Every area was searched until the entire study
site was covered.
 The search pattern was randomized each
observation night so that each area was
searched at different times of the night.

16.  Only scorpions found on the surface of the
ground or on vegetation were used for the
study.
 There was no removal of debris, bark, or rocks
to uncover scorpions in refuges.

17.  Scorpion size class was determined by length.
• Class I - < 5 mm
• Class II - 5 to 10 mm
• Class III - 10 to 15 mm
• Class IV - > 15 mm
 Only size class IV was collected.
 Females carrying young were not collected.
 Scorpions were collected with forceps and
placed in a Whirl-Pak® (Nasco).

18.  The scorpions were measured with calipers and
rounded to the nearest 1 mm.
 The sex was determined by size and sexual
dimorphism of metasomal segments.
 Scorpions were marked with Sharpie® markers
on the last segment of the mesosoma and two
segments of the metasoma.

19. N McReynolds 2009

21.  Marked scorpions were released the next
morning where collected.
 Data was obtained and recorded for every
“recaptured” scorpion
 Recorded data included date and time
observed, height of scorpions on vegetation,
position relative to flags, prey captured, prey
taxa, and behavior.

23.  The most common and easiest method for
estimating home range.
 Method consists of using points of data to
create a convex polygon that includes all data
points (Mohr 1947).
 The area of the polygon is the home range
estimate (used for 31 individuals).

25.  This method is used to identify hard
boundaries (e.g. a river) when estimating
home ranges (Getz and Wilmers 2004).
 Polygons (hulls) are created within the home
range using the k-1 nearest neighbors of each
data point.
 These hulls are then combined to estimate the
home range.

28.  Calculate the “center of activity” of an animal
(Hayne 1949).
 Create concentric circles around the center point.
 The space between circles are considered
probability contours (zones) within which the
animal spends varying proportions of its time.
 Calculating the area of the circle that contains up
to 99% of the data points is the home range.

30.  The overall recapture rate of Centruroides
vittatus was about 50%.
 Of those recaptured, 46% were male and 54%
were female.
 Smaller scorpions (15-17 mm) had the highest
rate of no recapture.

35.  MCP areas of males and females were
compared. (Female: µ = 25.41, n = 21, sd =
5.23; Males: µ= 91.65, n = 10, sd = 4.27).
 An unpaired t-test using natural log
transformation showed that the areas among
males and females were significantly different
(t = 2.095, df = 29, P < 0.05).
 Males had significantly larger areas than
females.

36.  Mean distances travelled between recaptures
of males and females were compared (Female:
µ = 819.31, n = 21, sd = 564.19; Males: µ=
1619.9, n = 10, sd = 1151.6)

 (Mann-Whitney Test, U = 55.0, U’ = 155.0, P <
0.05)
 Males moved significantly greater distances
between recaptures.

45.  Why was recapture rate so low?
• 15-17 mm scorpions were recaptured the least.
 Penultimate scorpions (molted the mark)
 Intra-guild predation
• Male and female recaptures were about the same.
 Male recapture should have been higher because they are
more active during mating season.
 Males may have wandered out of the study site.
• Low levels of surface activity are common for both
male and female scorpions.

46.  Why do males have larger home ranges?
• Males occupy more space in search of mates
• Female carrying young will hide to protect the offspring
 What is the difference in home range shape
between Centruroides vittatus and Smeringus
mesaensis?
• Desert scorpions have a circular home range while C.
vittatus have irregular home range shapes.
• Sandy desert habitats are homogenous while chaparral
habitats are heterogeneous.
• C.vittatus do not make their own burrows, so they must
find refuge wherever they can.

47.  How did the methods work in the area?
• MCP
 Outliers affect outcome
 Home range is overestimated
 Helps establish size for study area of C.vittatus. At least 1
hectare.
• LoCoH
 Requires at least 6 points to create two polygons (per
individual)
 Small polygons within home range show areas of higher use.
 Can be compared to distribution of vegetation or other
factors.

48. • CPZ
 Requires at least 10 data points
 Would work better with desert scorpions because of circular
home range
 Assumes a normal distribution from a central point of activity
(e.g. burrow)
 Irregular shapes with a more linear distribution can be
overestimated
 Method works when there are multiple centers of activity

49.  Larger study area.
 Observations on consecutive nights.
 Seasonal changes in home range.
 Compare home range to distribution of
vegetation.
 Use other methods for estimating home range.

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 Getz, W.M. and C.C. Wilmers. 2004. A local nearest-neighbor
convex-hull construction of home ranges and utilization
distributions. Ecography 27:489-505.
 Hadley, N. F. and S. C. Williams. 1968. Surface activities of some
North American scorpions in relation to feeding. Ecology
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 Hayne, D.W. 1949. Calculations of size of home range. J. Mammal.
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51.  McReynolds, C. N. 2004. Temporal patterns in microhabitat use for
the scorpion Centruroides vittatus (Scorpiones:Buthidae).
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Oecologia 67:273-277.
 Polis, G. A. 1990. Ecology. Pgs. 247-293 in G. A. Polis, ed. The
Biology of Scorpions. Stanford University Press, California.