Slow worm - Anguis fragilis

[Ceratodromeus]

Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Reptilia
Order: Squamata
Suborder: Lacertilia
Family: Anguidae
Genus: Anguis
Species: A.fragilis

Description
Contrary to the common name of this animal, it is not a worm, but a species of lizard. The common name arises from the animal's 'freezing' posture when confronted, or they move very slowly. At first glance many will assume this animal to be a snake, However, it can be distinguished from a snake via the possession of moveable eyelids as well as many anatomical differences, really all but helps the casual observer. These animals are a light brown to a grey in coloration. A single dorsal stripe running from about the nape of the neck to the tail is present in some, but not all, animals. Some animals possess a speckled white and brown coloration on the ventral side of the body and on the sides as well, and further others possess darkly pigmented, singular stripe running the animal's length. Very rarely, you will see a "blue spotted form" pop up in a population{3}.



The eyes and nostrils are small. Adult females tend to be slightly longer then the males, also being heavier; a population from the Netherlands, for example, had a sample of 66 adult females ranged from 131-385mm(5.1-7.2in)averaging 156(6.1in) in SVL. Total length ranged from (10.6-15.1in), with an average of 330mm(12.9in){2}. Out of a sample of 19 animals from the same study area, SVL ranged from 120-179mm(4.7-7.0in), averaging 142mm(5.5in). Total body lengths for males ranged from 258-301mm(10.1-11.8in), avering 282mm(11.1in){2}. Large animals have been documented at 431-457mm(17-18in) in total length{1}. Weights for adult females of this population with complete tails ranged from 13-26g(0.4-0.9oz), averaging 19.4g(0.6oz). In males with complete tails, weights ranged7.4-11.4g(0.2-0.4oz), averaging 8.5g(0.29oz){2}.


Geographic distribution & Habitat
This is a very widespread, very successful species of lizard. They can be found from Southwestern Europe(namely Spain), to Turkey, and even Iran. They are semi fossorial in nature, spending alot of time under ground in burrows crafted by small mammals, under logs, or under rocks. During the cooler months, they will spend most of their time in these retreats. However in the warmer months, they can be observed basking in direct sunlight on top of these retreats. Cloacal temperatures taken in a study on an alpine population ranged from 22-31 degrees Celsius(71-88 degrees fahrenheit)in gravid and non-gravid females{4}. In urban areas they can be commonly found in the soil of people's gardens.



Dietary habits
The slow worm preys on a wide range of invertebrates. Various Lepidoptera, Hymenoptera, Diptera, and Coleopteran larvae, Ants, bees, wasps, Springtails, scorpions, spiders and millipedes have all been recorded as food for this lizard. However, they seem to have a very strong preference for slugs, snails, and earthworms -- which singularly make up significant portions of the animal's diet{1,5}. The way in which they take slugs is slow and deliberate, and they will poise themselves over their chosen prey animal, grab it around the midsection, drag it a short distance, and then proceed to swallow it.



Behaviors
If they are feeling exposed, these animals will either freeze in their tracks, or begin to try and move away very slowly -- this is in part where their common name comes from. If they are grabbed or otherwise bothered, slow worms will readily discard(automotize) their tails, in a bid to distract whatever is harassing them. They are also known to bite people if they are handled{1}. Otherwise, if they are spotted and pursued, they will try and move away with surprising speed. One juvenile was documented diving into a puddle after being pursued by an observer{6}.

Reproduction
Slow worms are viviparous, meaning they give birth instead of laying eggs. When they are born, the young must break through a thin membrane casing that artificially resembles an egg. Females give birth in August or September, and their litter varies greatly and is likely tied to the size of the female. A litter can range from as little as four to as many as twelve; these young animals will measure around two inches in total length typically{1}. There is little to no level of parental care demonstrated by the female, though she may stay coiled in the birth site with the young for around a day{7}. After this, the young are independent and will disperse themselves.


References
{1} Leighton, Gerald Rowley. The Life History of British Lizards: And Their Local Distribution in the British Isles. George A. Morton, 1903.
{2} Stumpel, Anton HP. "Biometrical and ecological data from a Netherlands population of Anguis fragilis (Reptilia, Sauria, Anguidae)." Amphibia-Reptilia 6.2 (1985): 181-194.
{3} Capula, Massimo, Luca Luiselli, and Ernesto Capanna. "The blue‐spotted morph of the slow worm, Anguis fragilis: Colour polymorphism and predation risks." Italian Journal of Zoology 64.2 (1997): 147-153.
{4} Capula, Massimo, and Luca Luiselli. "Ecology of an alpine population of the slow worm, Anguis fragilis Linnaeus, 1758. Thermal biology of reproduction." Herpetozoa 6.1/2 (1993): 57-63.
{5} Pedersen, Iben Lindegaard, Jan Kjærgaard Jensen, and Søren Toft. "A method of obtaining dietary data for slow worms (Anguis fragilis) by means of non‐harmful cooling and results from a Danish population." Journal of Natural History 43.15-16 (2009): 1011-1025.
{6} Gollmann, Günter, and Birgit Gollmann. "Diving in the lizards Anguis fragilis and Lacerta agilis." North-Western Journal of Zoology 4.2 (2008): 324-326.
{7} Greene, Harry W., J. Jesús Sigala Rodríguez, and Brian J. Powell. "Parental behavior in anguid lizards." South American Journal of Herpetology 1.1 (2006): 9-19.

[Ceratodromeus]

In the OP i discussed blue coloration being sporadic in populations, well here's a neat article on the complete ventral side of Poland slow worms being completely blue -- one animal in particular that was photographed was a gravid female with an automotized tail.

"Animal coloration has long been a subject of study for many branches of biology. One of the colors that has received a lot of attention is blue. It occurs in many animals, can be perceived by many taxa, and has numerous potential functions (Bagnara et al. 2007; Umbers 2013). Presence of blue coloration has long been known in the slow worms (Schreiber 1875), legless lizards of the genus Anguis, mostly in the form of spots on the dorsal side of the body (e.g., Capula et al. 1997; Sos 2011; Wermuth 1950). Slow worms have sexually dimorphic coloration. Females generally have sharp dorsolateral contrast, a vertebral line, and a black colored abdomen, similar to immature individuals. Males are generally brighter than females, lack dorsolateral contrast and a vertebral line, and have bright colored abdomen (Arnold and Ovenden 2003; Beebee and Griffiths 2000; Dely 1981; Sos 2010). Blue coloration of the venter seems to be rare and is seldom described in the literature. Only Beebee and Griffiths (2000) stated that in both sexes of the slow worm (Anguis fragilis) bluish abdomens may be present. However, they do not provide details on the form or extent of that coloration. Other authors describe blue either as being present only in some males (e.g., Dely 1981; Sos 2011) or absent in both sexes (Arnold and Ovenden 2003). Some authors describe species as a whole—at least in respect to ventral coloration—rather than each sex separately, so potential color dimorphism of this trait cannot be assessed (Schreiber 1875; Wermuth 1950). Color pattern of the slow worm shows ontogenetic and seasonal variation (Capula et al. 1997; Sos 2011) which may be a reason for this ambiguity. Moreover, Anguis fragilis has recently been split into several species (Gvoždík et al. 2010, 2013), so many pre-2010 publications have to be taken as a description of a species complex rather than of A. fragilis itself. A completely blue venter is the most exceptional form of such coloration. Recently, the first record of an eastern slow worm (A. colchica) with the
same color form was described (Jablonski and Meduna 2010). Here, we describe other such specimens that indicate that this coloration may be more widespread than previously assumed.
Material and methods.—
Ślęża
Landscape Park is a protected area located in
Lower Silesia, south-western Poland (Fig. 1).
It includes Ślęża Massif (with Ślęża, 718 m
a.s.l., being the highest peak), an isolated
mountain massif in the Sudetes Foothills, that
spans an area of 81.9 km2. Despite being in
a small, isolated region, its herpetofauna
includes more montane than lowland taxa
(Majtyka et al. 2010). The slow worm is
a common animal in the Ślęża Landscape
Park and the blue-spotted form has a high
frequency (about 25%) within the population
(Majtyka et al. 2010). However, no specimens
with blue venters have been recorded from
that locality. The specimens described in this
article were caught by hand, photographed,
and measured. Snout-vent length (SVL) and
total body length were recorded and number
of scale rows along the midbody were
counted.
Results and discussion.—An adult
female slow worm was found on 31 May
2015—a warm (22ºC) and sunny day—on
a south-facing slope (50.8960°N, 16.7166°E,
250 m a.s.l.) approximately 1 km south of
Sobótka. The female was gravid and had an
autotomized tail (SVL = 18 cm, retained tail
length = 11 cm). Dorsal side of the body
brown, with dark sides and dark stripe along
the backbone (Fig. 2A), prefrontal scales in
broad contact (type A pileus), 25 scale rows
around the midbody, an indistinctive ear
opening—a combination of traits
characteristic for Anguis fragilis (Gvoždík et
al. 2010, 2013; Sos 2010). Blue ventral
coloration was extending the entire length of
the body and abruptly disappearing dorsally
(Fig. 2B). The female behaved aggressively
and tried to bite when handled. The second
individual was caught on 11 June 2015
(sunny, 24ºC) under a sheet of plastic in
a private backyard in Sulistrowiczki
(50.8333°N, 16.7166°E, 291 m a.s.l.), where
common lizard (Zootoca vivipara), grass
snake (Natrix natrix), and other adult slow
worms were also present. The slow worm was
a gravid female (SVL = 18.5 cm, total length
= 39.5 cm). Prefrontal scales contacting
medially only at a point (type B pileus), 26
scale rows around the midbody, an
indistinctive ear opening—also a common
trait combination in Anguis fragilis (Sos
2010). Dorsal coloration the same as in the
first specimen, blue ventral scales lighter than
in the first female and did not cover the
ventral part of the mandible but did extended
to the tail tip (Fig. 2C). After taking the
measurements and photographs, both animals
were released. During those two trips to the
Ślęża Landscape Park, over twenty slow
worms have been observed but only these two
individuals had the distinct blue ventral
coloration.
In many species of lizards blue occurs
mostly or only in males. This suggests that
blue coloration may have a role in sexual
selection, yet there are lizards where both
sexes are blue (Bagnara et al. 2007; Pérez i de
Lanuza and Font 2010). Blue coloration of
ventral abdomen in male phrynosomatid
lizards is produced by elevated levels of
testosterone. Supplementing females with
exogenous testosterone leads to production of
male-like coloration (Cox et al. 2005; Quinn
and Hews 2003). In some iguanians and
lacertids such male-like coloration in gravid
females allows them to avoid potentially
harmful copulations (Cooper and Greenberg
1992; Galán 2000). However, while blue
abdomens are more common in males than in
females (see above and Sos 2011), completely
blue venters are very rare even in males. They
were described only in an adult male of
A. colchica from eastern Czech Republic
(Jablonski and Meduna 2010) and recently
a male from Lutcza in south-eastern Poland
(G. Skórzewski, pers. obs.). In addition, in
a population of A. colchica from Romania
blue abdomens were present only in males
(Sos 2011). This suggests that completely
blue venter—if not just abnormal
coloration—may be a non-adaptive byproduct
of unusually high level of sex hormones.
However, discovery of more specimens with
such coloration could indicate that it plays
some role in intraspecific communication, as
in many lizard species.
The slow worms from Ślęża
Landscape Park are the first records of
a completely blue ventral coloration in
A. fragilis (sensu stricto). They were also the
first females in the whole species complex
with such coloration. Individuals were located
~135 km further west than the previous
westernmost locality of that color form. This
suggests that frequency of such coloration
may be underestimated and that it is not
restricted only to males or only to A. colchica.
However, explaining its causes and function
in slow worms requires further studies."

Cite:
KACZMAREK, PAWEŁ, TOMASZ SKAWIŃSKI, and GRZEGORZ SKÓRZEWSKI. "Blue venter in the slow worm (Anguis fragilis): review and new data." Herpetological Review (2016): 1.