By: Jose Luis Chapa

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)

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)

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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)

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)

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.

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.

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.

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.

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.

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.

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).

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.

N McReynolds 2009

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

• 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

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.

Audy, J.R. and J.L. Harrison. 1954. Collections made in Malaya by the Colonial Office Scrub Typhus Research Unit. Studies from the Institute for Medical Research, Malaya, 26:1-22.

Blair, W. F. 1950. The biotic provinces of Texas. Texas Journal of Science 2:93-117.

Burt, W.H. 1943. Territoriality and home range concepts as applied to mammals. Journal of Mammalogy 24:346-352

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 49:726-734.

Hayne, D.W. 1949. Calculations of size of home range. J. Mammal. 46:398-408.

McReynolds, C. N. 2004. Temporal patterns in microhabitat use for the scorpion Centruroides vittatus (Scorpiones:Buthidae). Occasional Publications in Scorpiology 17:35-45.

McReynolds, C. N. 2008. Microhabitat preferences for the errant scorpion, Centruroides vittatus (Scorpiones, Buthidae). The Journal of Arachnology 36:557-564.

Mohr, C.O. 1947. Table of equivalent populations of North American small mammals. Am. Midl. Nat. 37:223-249.

Polis, G. A., C. N. McReynolds, and R. Glenn Ford. 1985. Home range geometry of the desert scorpion Paruroctonus mesaensis. 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.