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24 IGUANA  •  VOLUME 15, NUMBER 1  •  MARCH 2008 RIVAS

Black Iguanas (Ctenosaura similis) are among the most visible of Costa Rican reptiles, occurring in various habitats throughout the country.



Reptiles can be exposed to various ectoparasites, some of
which carry diseases or otherwise negatively affect their

populations (Hanley and Stamps 2002, Wikelski 1999).
Conventional wisdom suggests that animals with high parasite
loads must be in worse physical condition than animals with
lower infestations, but this assumption has not been docu-
mented in many reptiles. In the United States, a number of
exotic ectoparasites have been introduced with their reptilian
hosts (Burridge and Simmons 2003). Predicting the fates of
these reptile-associated introductions is difficult without greater
knowledge of the parasite-host systems. Data presented here on
tick infestations of free-ranging Black Iguanas (Ctenosaura sim-
ilis) from Palo Verde National Park, Costa Rica will add to the
general body of knowledge for these kinds of systems.

In July 1996, I caught 20 C. similis (mean = 873 g,
240–2,080 g) near the Organization of Tropical Studies (OTS)
Palo Verde Biological Field Station (10°21'N, 85°21'W; eleva-
tion ~10 m) by noosing them on branches or capturing them by
hand in holes. Each animal was measured (SVL, to nearest cm),
weighed (to nearest g), and the ticks on each were counted and
classified visually into three size classes: small (< 2 mm), medium
(2–4 mm), and large (> 4 mm). I also classified the shedding sta-
tus of the iguana as recently shed, old shed, or shedding,
depending on whether they had bright new skin without rem-
nants of an old shed, some remnants of shed at the joints, or
widespread larger patches of shedding epidermis, respectively. I
used a non-parametric Kruskall-Wallis test to compare the
effects of the shedding status on the number of ticks. The Fulton

Ticks (Amblyomma spp.) on Black Iguanas
(Ctenosaura similis) in Costa Rica

Jesus A. Rivas

Department of Mathematics and Natural Sciences, Somerset Community College, Somerset, Kentucky

IGUANA  •  VOLUME 15, NUMBER 1  •  MARCH 2008 25TICKS ON BLACK IGUANAS

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Even heavy tick infestations on free-ranging Black Iguanas (Ctenosaura similis) in Costa Rica seem to have little effect on the lizards’ body conditions.

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Index (Bolger and Connoly 1989) is a condition index that is
calculated by dividing the mass of an individual by the cubic
power of its length. I used Spearman correlation tests to assess
the effects of tick infestations on the condition of the ctenosaurs
and the effects of body size on the number of ticks present per
individual.

I recorded two tick species on C. similis: Amblyomma scu-
tatum and A. dissimile. Amblyomma scutatum was more abun-
dant than A. dissimile. The mean number of ticks per animal
was 56 (0–217). Only one animal did not carry ticks. I found
no significant relationship between the total number of ticks

26 IGUANA  •  VOLUME 15, NUMBER 1  •  MARCH 2008 RIVAS

Number of ticks in each size class found on the different sizes of
Ctenosaura similis in Palo Verde National Park, Costa Rica.

Ticks (Amblyomma scutatum, top; A. dissimile, bottom) embedded in the skin of Black Iguanas.

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Percentage of each tick size class found on the different sizes of
Ctenosaura similis in Palo Verde National Park, Costa Rica.



and the size of individual ctenosaurs (r = 0.18, P = 0.46; N =
20), but smaller C. similis seemed to have more small ticks, and
medium-sized ticks seemed to be more abundant on larger
ctenosaurs. Large ticks occurred in relatively low numbers
across all sizes of ctenosaurs. Four animals had shed recently,
seven were in the process of shedding, and eight had old skins.
I found no significant differences in the number of ticks among
the three shedding categories (Kruskall-Wallis test; �2 = 0.69, 
P = 0.71).

Most of the study animals had a heavy tick load, but heav-
ily infested animals did not appear to be in poorer physical con-
dition. No correlation existed between the number of ticks and
the condition of the animal as estimated with Fulton’s Index (r =
-0.38, P = 0.10; N = 20), suggesting that ticks may not be a bur-
den to healthy ctenosaurs. Both this lack of relationship and the
lack of relationship between shedding status and the number of
ticks were unexpected. Both findings could be explained by a fast
turnover of ticks on individual ctenosaurs, where each tick may
spend but a short time on a given animal before attaching itself
to another animal that has just shed. In view of the large num-
ber of exotic animals moving across national boundaries due to
the pet trade, we must consider the potential effect of seemingly
healthy animals introducing their parasites as well.

Acknowledgments
Data were collected during the OTS Course 96-3. James Keirans
identified the tick, Eric Olson and members of the OTS course
helped in the field, and Sarah Corey provided helpful editorial
comments.

References
Bolger, T. and P.L. Connoly. 1989. The selection of suitable indices for meas-

urement and analysis of condition. Journal of Fish Biology 34: 171–182.

Burridge, M.J. and L.A. Simmons. 2003. Exotic ticks introduced into the
United States on imported reptiles from 1962 to 2001 and their poten-
tial roles in international dissemination of diseases. Veterinary Parasitology
113: 289–320.

Hanley, K.A. and J.A. Stamps. 2002. Does corticosterone mediate bidirectional
interactions between social behaviour and blood parasites in juvenile
Black Iguanas, Ctenosaura similis? Animal Behaviour 63: 311–322.

Wikelski. M. 1999. Influences of parasites and thermoregulation on grouping
tendencies in Marine Iguanas. Behavioral Ecology 10: 22–29.

Sonoran Mountain 
Kingsnake Survey

The Nevada Department of Wildlife and Great Basin
National Park are pleased to announce the 3nd Annual
Great Basin Sonoran Mountain Kingsnake Survey on
12–16 May 2008. For more information contact:
Bryan Hamilton (bryan_hamilton@nps.gov).

IGUANA  •  VOLUME 15, NUMBER 1  •  MARCH 2008 27TICKS ON BLACK IGUANAS

Ticks frequently found on Black Iguanas (Ctenosaura similis) in Costa
Rica: Amblyomma scutatum (left) and A. dissimile (right). 

Unlike ctenosaurs in Palo Verde National Park, those in the dry forest
in Puntarenas often are free of parasites. This individual had sought
shelter in the hollow core of a fallen tree.

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The Sonoran Mountain Kingsnake (Lampropeltis pyrome-
lana) inhabits rocky mountain habitats from 850–2,800
m in the western United States and adjacent regions in
Mexico.

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