History and origin
The Moor frog was first described by Nilsson in 1842, the scientific name of this species is Rana arvalis. Rana is Latin and means frog. Arvalis is also Latin and means 'of the fields'.
Characteristics
This species is characterised by the males blue coloration during the breeding season.
Description =Size=
- Eggs: The eggs measure about 1.5 to 2 mm in diameter, they are laid in separate balls that measure about 6 to 8 mm in diameter.
- Tadpoles: The tadpoles measure 3 to 5 mm long when they exit the egg. Maximum sized tadpoles measure about 45 mm long.
- Juveniles: The juveniles measure 12 to 16 mm long when they exit the water.
- Adults: Adults measure up to 70 mm long. However they average about 55 to 60 mm long. =Morphology=
- Eggs: The eggs are laid in individual balls in 2 or 3 clusters of up to 2000 eggs, a total of about 4000 eggs are laid per female.
- Tadpoles: They have a quite tall tail that doesn't come onto the back. The tail ends in a sharp point.
- Adults: This is a small, bulky frog with a short and pointed snout. Their skin is smooth and they have prominent dorsolateral folds. They have short limbs. They do not have paratoid glands. Their hind feet webbing is average. Their pupils are horizontal. Their vocal sacs are internal in males and makes for a loose throat. =Patterns & colours=
- Eggs: They are greyish, brownish or dark olive on the upper side, with a large white, yellowish marking on the underside.
- Tadpoles: The upper body is brownish, the belly is light in colour.
- Adults: Males are usually more uniform and dull in colouring where as females tend to be more vivid. They are usually yellowish, brownish with very dark irregular small markings on the flanks, on the back there is usually a lighter line running down the middle of the back, this colour is usually a lighter shade of the back colour. They have a 'bandit-like' black marking running through the eyes from the nose and back towards the ears. The more dull specimens are usually brownish, reddish in colour with the 'bandit-like' marking across the eyes. They belly is white but sometimes has irregular small dark markings on it. Their eyes are golden.
Geographical range Found over most of central and eastern Europe. Absent from the Balkans and from the Alps, this species in Norway is only found in the south of the country, it's western limits are Alsace in France, Belgium, the Netherlands, southern Germany, the most southern point in the range is in northern Croatia and Romania.
Subspecies - arvalis - They are found in the northern half of the range.
- wolterstorff - They are found from southern Poland southwards into Austria, Romania, southern Russia...
Sexual differences
Males have during the breeding season nuptial pads (greyish in colouring) on their thumbs. Males front legs are more robust then females front legs. Males have a small pair of internal vocal sacs.
Seasonal variations
Males become bluish during the breeding season as well as developing nuptial pads. Outside of the breeding season, identifying the males from the females is more difficult. In early spring the specimens are usually dark in colour, becoming lighter with time.
Diet
They feed on a large proportion of insects, spiders and even snails.
Defensive habits
During the breeding season they are very discrete and hide at the slightest alert. If touched they often flatten themselves onto the ground and raise their limbs, covering their eyes with their front legs. They may also emit a distress call.
Reproduction
Around the beginning to mid March the migration to the breeding sites begins and it is interesting to note that even young specimens who have not reached sexual maturity also take part in this. Males are first on site and they stay for longer then the females who leave after laying their eggs. Breeding sites are usually streams, flooded fields, ponds, temporary water holes, the depth of these sites is rarely more then 50 cm deep. When the male finds the female he holds onto her under her front legs and has his hands on her chest, the male is now "glued" to the females back. The female then feels the time has come to push her eggs out so she moves over to a vegetated area in the water, ejects all of her eggs at one time which will glue to each other and sometimes be as large as a persons head. As the eggs come out of the female the male fertilizes them. The couple separate just after the expulsion of the eggs.
Sexual maturity, life span
The average life span for Rana arvalis is about 11 years, they reach their sexual maturity in their third year.
Habits
Males are very active by day in the breeding season, Around the beginning to mid March the migration towards the breeding sites begins, they migrate to their summer habitat around about mid April to mid May. During mid summer they may be found next to rivers and other water holes where Pelophylax frogs are common.
Call
A fast calling 'wuog...wuog...wuog...' sounding like someone is making bubbles in a glass of water, there maybe up to 7 impulsions per second. Males often sing in shallow parts of the water or on top of floating vegetation, sound (p)www.oreilleverte.com:
Habitat
Found under 800 m in altitude. They live in preference in areas with underground water, they are usually found at the edges of fields that often flood. Also found in humid fields. They usually breed in streams, flooded fields, and any other water hole nearby. Sometimes they lay their eggs in temporary water holes, their preferred water holes are well exposed.
Predators
Birds are a great danger. Otherwise water insects often eat the eggs/tadpoles and we must suppose that Natrix natrix prey on adults.
Found over most of central and eastern Europe. Absent from the Balkans and from the Alps, this species in Norway is only found in the south of the country, it's western limits are Alsace in France, Belgium, the Netherlands, southern Germany, the most southern point in the range is in northern Croatia and Romania. 
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