It is one of the most ubiquitous snake species, both in Romania and Europe. [2, 3, 6]The species can be encountered all over the Romanian territory, from the sea level to altitudes of 1,100. [2, 3] Morphology. Slender, average to large snake, over 1 meter long (it can also reach 2 meters). The rostral is wide, the internasals are trapezoidal, the frontal’s length is larger than its width and it is separated from the preocular. The surlabials count as 7 (rarely 8), the 3rd and the 4th lounging the eye. A single preocular and 3 superposed postoculars (rarely 2 or 4) behind which a long narrow shield can be seen. The dorsal scales have an obvious longitudinal keel, lined in 19 rows. The ventral scales vary from 163 to 183, and the subcaudals count from 53 to 78 pairs. [2, 3, 6]
The dorsal colour varies from grey to brown or black. The dorsal pattern is missing or it can be formed of 4-6 longitudinal rows of small black spots. The posterior cephalic region is differentiated by two semicircular spots, with colours varying from white to yellow or orange. The ventral colour is black and white. Sometimes melanistic specimens can be encountered (completely black back) with greyish black abdomen. In Dobrogea and the southern Romania a variety with two dorsal-lateral whitish or yellowish stripes is frequently encountered. The stripes are two scales wide and the abdomen in this variety is completely black (Natrix natrix var. persa). [2, 3]
Ecology. It is a diurnal species, leading both a terrestrial and aquatic way of life. It can be encountered near the water (ponds, swamps, rivers), as well as considerably far away from it, in dry, stone rich areas, in the fields or in the forest. It prefers sunny spots, with cover vegetation. When spotted, its first reaction is flight, hiding in holes and cracks, or, if near water, diving in it. If it cannot hide, it will assume an aggressive attitude, intimidating for those who are not familiarised with the species, quenching in a circle, hissing loudly and hitting the aggressor with its head, but without biting. If manipulated, it will release the contents of its foul smelling anal glands and if the stress factor does not cease, it will fake death, coiled on its back with its tongue sticking out (see picture below). It feeds on newts, frogs, fish, mammals and small birds. It is an antropophilic species, living in the proximity of human settlements (hence the vernacular name of the species in Romanian, `house snake`) often hiding in cracks of the floor or walls, in the attics or basements. Its natural enemies count water birds, birds of prey, hedgehogs, etc. It hibernates in groups of several individuals from October to April. [2, 3, 6]
Reproduction takes place in the months of April and May. The eggs are buried in shallow nests, in soil, leaves, moss, decomposing straws etc. during July-August and is usually formed of 11 to 25 white eggs sticking together. Common nests being used by several females at the same time were reported. After approximately 10 weeks, the juveniles hatch, having a length of approximately 160-190 mm. [2, 3]
Legislation. In Romania, the species is protected by Law 13 of 1993, by which Romania ratified the Bern Convention (Annex III). 
According to the IUCN classification, worldwide the species’ status is least concern (LC), and in the Romanian Red Book of Vertebrates the species is recorded as non-evaluated (NE). [5, 8]
2. Fuhn I.E., Vancea Ș., (1961): Fauna R.P.R. Reptilia (Țestoase, Șopârle, Șerpi). Vol XIV, fasc. 2, Editura Academiei R.P.R., București. [in Ro]
3. Fuhn I.E., (1969): Broaște, șerpi, șopârle. Ed. Științifică, București. [in Ro]
4. Gasc J.P., Cabela A., Crnobrnja-Isailovic, Domen D., Groessenbacher K., Haffner P., Lescure J., Martens H., Marinez Rica J.P., Maurin H., Oliveira M.E., Sofianidou T.S., Veith M., Zuiderwijk A., (1997): Atlas of Amphibians and Reptiles in Europe. Societas Europaea Herpetologica & Museum National d’Histoire Naturelle Paris.
5. Iftimie A., (2005): Reptilia. In: Botnariuc & Tatole (eds): Cartea Roșie a Vertebratelor din România. Ed. Academiei Române, București. [in Ro]
6. Kindler C., Böhme W., Corti C., Gvoždík V., Jablonski D., Jandzik D., Metallinou M., Široký P., Fritz U., 2013: Mitochondrial phylogeography, contact zones and taxonomy of grass snakes (Natrix natrix, N. megalocephala). Zoologica Scripta 42: 458-472.
7. ***Legea 13 din 1993 prin care România ratifică Convenția de la Berna. [in Ro]
8. *** www.iucnredlist.org