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Introduction

A chart & photo's showing the differences between Elaphe bimaculata, Elaphe dione & Oocatochus rufodorsatus.

One question that is asked time and time again on internet forums " Is my snake a Dione Ratanske, Elaphe dione or Twin Spotted Ratsnake, Elaphe bimaculata". It is always a difficult one to answer by a photograph alone as the appearance of these two species is very similar. A third species although not as common in the hobby these days is the Red backed Ratsnake, Oocatochus rufodorsata which also bears a resemblence to the latter two species. The chart below gives a comparison of these three species which may prove useful in identifying the exact species, but as can be seen there are alot of characteristics that are the same or overlap.
 

 
Elaphe dione Elaphe bimaculata Oocatochus rufodorsata
Postoculars

2-3

2 2 Rarely 3
Temporals 2+3 or 2+4 2+2 or 2+3 2+2 or 2+3 or 3+3, rarely 1+3, 2+1, 2+4, 1+4
Preocular 1 1 1
Supralabials 8 Rarely 7 or 9 (4th & 5th or 5th & 6th touch the eye) 8-9 Rarely 10 (4th & 5th touch the eye) 7-8 Rarely 6 (3rd & 4th or 4th & 5th touch the eye)
Infralabials 10-12 8-10 Rarely 11 9-11
Anal Plate Divided Divided Divided
Ventrals 170-214
Lack keels
177-207
Weakly Keeled
154-187
poorly developed keels
Subcaudals 50-80 67-78 45-65
Dorsals midbody 23-27
Dorsal scales weakly keeled
23-25
Dorsal scales smooth or only weakly keeled
19-21
Dorsal scales smooth or only weakly keeled
Labials Chinese specimens may have lemon-yellowish flashing to the labials Generally lemon-yellowish  
Iris Yellowish Brown or Reddish Brown Golden Greyish Brown Golden Brown
Tongue Brownish Reddish Brown Dark Brown/Black with a rosy base
Ventral Colour Greyish, Yellowish or White sometimes with a rosy tinge with dark speckles or spots Greyish, Yellowish, in the striped phase speckled with dark spots. The blotched phase has disctinct black blotches on a yellowish ventral surface which intestify towards the tail Creamy white and speckled or scattered with dark spots.
Head Pattern U or W shaped head marking usually widening on the neck... Finishes at nape or only connects the first blotches and is always of an irregular shape V shaped with pointed ends usually very regular... Generally connects to several dorsal blotches V shaped ... Either connects to the dorsal blotches or ends in two blotches at the nape
Head Shape Broad and blunt Narrow and long  
Snout Rounded is approx twice as long as the eye diameter Rounded is approx twice as long as the eye diameter Rounded is approx one and a half times as long as the eye diameter
Dorsal Blotches Indistinct or faint black borders to the blotches Distinct black borders to the dorsal blotches  
Average Adult Size 60-70cm occasionally upto 120cm+ 60-80cm occasionally upto 120cm 50-70cm occasionally upto 90cm
Egg Incubation Time Average 25 days Average 40 days Live bearer


Credits:
Comparison Diagram: KDS

References:
1. A Monograph of the colubrid Snakes ofthe Genus Elaphe FITZINGER by Klaus-Dieter Schultz. 1996
2. Non Venomous Snakes by Trutnau
3. Asian Rat Snakes of the Elaphe Genus Pt.1 Elaphe rufodorsata 'Snake Keeper' Vol.2 No.2 February 1988 by Klaus-Dieter Schultz
4. Asian Rat Snakes of the Elaphe Genus Pt.5 Elaphe bimaculata 'Snake Keeper' Vol.2 No.6 1988 by Klaus-Dieter Schultz
5. Asian Rat Snakes of the Elaphe Genus Pt.4 Elaphe dione 'Snake Keeper' Vol.2 No.5 1988 by Klaus-Dieter Schultz
6. List of Chinese Turtles, Crocodilians, and snakes with keys by Clifford H.Pope
7. New Chinese amphibians and reptiles by Karl Patterson Schmidt 1925
8. The Evolution of Viviparity in Reptiles: An Ecolgical Analysis by Richard Shine
9. http://www.teraristika.cz/cz/terarista/3_1/02.html
 
This site has information on the following genera of Ratsnakes ... Spilotes, Spalerosophis, Ptyas, Zamenis, Elaphe, Rhinechis, Senticolis, Pseudelaphe, Pantherophis, Bogertophis, Orthriophis, Gonyosoma, Oreocryptophis, Oocatochus, Euprepiophis, Coelognathus, Archelaphe