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148 IGUANA  •  VOLUME 11, NUMBER 3  •  SEPTEMBER 2004 BURTON

Location of Grand Cayman in the north-west Caribbean, the
only island where Cyclura lewisi occurs. Illustration by John Binns.

Founder male Daniel, 13 years old at the time of this photograph, is breeding successfully in a large open-air pen at the Blue Iguana
Recovery Program’s captive breeding and head-starting facility on Grand Cayman. Photograph by John Binns.

Potential founder male, Hal, was until recently in illegal captiv-
ity and is now recovering from a decade of chronic malnutrition.
He mated in 2003 and 2004, but so far remains infertile.



In a recent paper in The Caribbean Journal of Science, I relied
on several different lines of evidence to formally conclude that

the Grand Cayman Blue Iguana is a full species, Cyclura lewisi.
The old classification, in which the Blue Iguana was considered
to be a subspecies of the Cuban Iguana (C. nubila), didn’t make
much sense after 2000, when Catherine Malone and her col-
leagues showed that Cuban Iguanas and the iguanas from Little
Cayman and Cayman Brac are, if anything, more closely related
to the Bahamian species (C. cychlura) than they are to Blues.

Apart from DNA, the most diagnostic feature distinguish-
ing the Blue Iguana is the color of adults. The remarkable bright

blue of adult C. lewisi was first described by Chapman Grant in
1940, but the color patterns of hatchlings and subadults have
never been reported in detail.

When they first emerge from the nest, Blue Iguana hatch-
lings are intricately patterned, very much like hatchlings of C.
nubila and C. cychlura. The head and dewlap are pale bluish gray
and unmarked, except in some individuals, which may show sub-
tle dark marks just behind the eyes. The interparietal scale (the
“pineal eye” in the middle of the back of the head) is particularly
pale, and the nostrils are narrowly rimmed with black. The iris of
the eye is golden and essentially fills the exposed area of the eye.
The surrounding sclera is reddish but rarely seen at this age.

Starting at the neck and proceeding down the length of the
body is a pattern of dark “chevrons” — looking down from
above, they appear as a series of V’s running diagonally back and
down both sides of the body. From the side, they look like diag-
onal dark stripes on a paler background, running from the neck
and back rearwards down the flanks to the belly. To some peo-
ple, they look like pale stripes on a dark background — I guess
it all depends on your point of view.

This pattern starts with an inconspicuous, very short, dark
gray chevron starting near the front of the incipient nuchal (neck)
crest. Viewed from above, this and a conspicuous second dark
chevron are U-shaped, curving over the neck crest. The ends of
the second chevron turn downward to stop above the front legs.
The third and subsequent chevrons are V-shaped from above and
somewhat wavy on the flanks, sometimes breaking up lower on
the sides. Eight chevrons usually are present between the begin-
ning of the nuchal crest and the pelvis, each becoming progres-
sively less distinct after the fourth.

The skin between the first and second chevrons is unmarked
silvery gray, becoming pale cream away from the nuchal crest.
After the second chevron, from the rear edge of each dark band
the flanks are pale bluish gray, heavily mottled with dark gray.
The mottling gives way to a series of discrete small pale cream
spots, close to (but not usually in contact with) the front edge of
the next chevron.

Along the back, the chevrons connect to an alternating pat-
tern of near-black and pale cream spots down the middorsal line,
marking where the dorsal crest will emerge. The cream spots
begin as a single pale nuchal crest scale between the first and sec-
ond chevrons, followed by three progressively larger spots to the
third chevron, two large spots to the fourth, and a single spot
between subsequent chevrons. Black scales between these spots

Color and Pattern in 
Grand Cayman Blue Iguanas

Fred Burton

Blue Iguana Recovery Programme, Grand Cayman Island

Photographs by author, except where indicated.

IGUANA  •  VOLUME 11, NUMBER 3  •  SEPTEMBER 2004 149GRAND CAYMAN BLUE IGUANAS

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Newly hatched Cyclura lewisi: at this age the hatchling is still con-
suming its yolk sac and has not started feeding.



are continuous with chevrons, where those occur, and otherwise
form isolated dark spots. This complex arrangement creates a
bold alternating pattern down the middorsal line.

The series of cream spots continues onto the tail, merging
into an alternating series of narrow pale cream bands and broad
dark gray bands around the upper two-thirds of the tail. The end
of the tail is almost black.

The legs have extensive cream mottling and pale bluish gray
flecks on a dark gray base, with distinct cream spots particularly

evident on the rear legs and feet. Pale cream spots extend onto
the toes, where they coincide with the joints, making the toes on
both front and rear feet appear banded. The underside of the
abdomen is silvery gray with the pale, fragmented ends of the
strongest chevrons from each side almost meeting beneath.

By one year of age, the bluish gray and gray base colors have
become clear blue and the chevrons have begun to erode, nar-
rowing and breaking up into spots on the lower flanks, where
they may become circles exposing a center of blue. The back is

150 IGUANA  •  VOLUME 11, NUMBER 3  •  SEPTEMBER 2004 BURTON

Spots on the legs, still evident at one year, usually disappear completely as the animal ages.

Adult female C. lewisi: juvenile markings have been lost.



IGUANA  •  VOLUME 11, NUMBER 3  •  SEPTEMBER 2004 151IGUANA  •  VOLUME 11, NUMBER 3  •  SEPTEMBER 2004 151GRAND CAYMAN BLUE IGUANAS

speckled with isolated pale cream scales and the flanks between
chevrons are still marked with diffuse pale cream spots. The blue
base color is progressively obscured by dark gray on the tail, where
the banding becomes less distinct with age. The alternating cream
and black pattern on the dorsal crest is reduced but still evident.

The juvenile pattern changes to the adult form gradually, by
further replacement of cream spots and speckling with the blue
base color and the variable loss of the dark chevrons (some adults
lose them entirely). Limbs also become blue, apart from the toes,
which lose all banding and darken to black. The nuchal and dor-
sal crest scales all become bright blue, with no trace of the juve-
nile pattern. The lower half of the tail becomes darker, with band-
ing either totally obscured or very indistinct. The sclera of the eye
becomes redder and more exposed as the animal grows.

Having said all of that, a Blue Iguana is only blue when it
wants to be blue. All that blue is masked in dark gray when an
iguana is cold, sleeping, or just trying to remain inconspicuous.
The gray color closely matches the surrounding carbonate karst
rock, on which iguanas seem to vanish into the landscape.

Watching these iguanas in the wild, they appear to use their color
selectively and carefully, as signals to each other. In the greens and
earth tones of Grand Cayman’s dry shrublands, the bright blue
of C. lewisi shines out like a beacon.

References
Burton, F.J. 2000. Grand Cayman Iguana, pp. 45–47. In A. Alberts (comp. &

ed.), West Indian Iguanas: Status Survey and Action Plan. IUCN, Gland,
Switzerland.

Burton, F.J. 2004. Taxonomic status of the Grand Cayman Blue Iguana.
Caribbean Journal of Science 40:198–203.

Grant, C. 1940. The herpetology of the Cayman Islands. Bulletin of the Institute
of Jamaica, Science Series (2):1–55.

Malone, C.L., T. Wheeler, J.F. Taylor, and S.K. Davis. 2000. Phylogeography
of the Caribbean Rock Iguana (Cyclura): Implications for conservation and
insights on the biogeographic history of the West Indies. Molecular
Phylogenetics and Evolution 17:269–279.

Schwartz, A. and M. Carey 1977. Systematics and evolution in the West Indian
iguanid genus Cyclura. Studies on the Fauna of Curaçao and other Caribbean
Islands 173:15–97.

S P E C I E S  P R O F I L E

Compared to their relatives in the families Boiidae and
Pythonidae, the Ground Boas of the genus Tropidophis

(Family Tropidophiidae) are relatively small and are sometimes
referred to as “dwarf boas.” The largest species reaches a total
length of barely over a meter and the smallest less than a third of
that length. Unlike most boas and pythons, Ground Boas lack
infrared sensors in interlabial pits, but, like their larger relatives,
they possess vestiges of hind limbs, which are visible externally as
a pair of cloacal spurs. All are live-bearers. They are ground-
dwelling or semiarboreal and feed primarily on small vertebrates,
mainly frogs and lizards. When disturbed, these snakes may
exhibit autohemorrhaging from the eyes and mouth as well as
cloacal discharge. On loose substrates, at least one species is
known to employ sidewinding locomotion. Many (maybe all)
species also are capable of physiological color changes, a phe-
nomenon that is rare in snakes. Ground Boas apparently are
unique among those snakes that can change colors in that they do
so on a 24-hour cycle: they are lighter in color at night and darker
during the day. All members of the genus are listed in CITES
Appendix II and are rarely seen in the pet trade.

Species of Tropidophis are relatively broadly distributed in the
West Indies and South America, but they are secretive.
Consequently, many are not well-represented in museum collec-
tions and their taxonomy has been poorly understood. Previous

Ground Boas (Tropidophis) of the Cayman Islands
A.C. Echternacht

Department of Ecology & Evolutionary Biology
University of Tennessee, Knoxville

Photographs by the author.

Adult Grand Cayman Ground Boa, Tropidophis caymanensis.


