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Sexual dimorphism?

There is no sexual dimorphisme in these snakes, except in the case of Malpolon. In this genus, females are directly at hatching much more clearly marked, on the supra- and infralabials, on top of the head and on the underside of the head. For further details see De Haan 1999.

Click on the pictures for details. 1-2: female; 3-4: male.

See for the subject of sexual dimorphism for instance Broadley 2002.

Sexing

Sex determination is not an easy job in these snakes. Characteristics as 'larger males' are not always useful, as young and small males exist, of course.
'Popping' of hatchlings is not recommended. However, it is possible for hatchlings, as was proven by Cesare Colli, who popped young Psammophis orientalis. Pictures:

Another method is the detailed observation of the cloacal region of the sheddings. In males, hemipenes often shed along with the rest, and can be observed. I made photographs of the sheddings of male Rhamphiophis rubropunctatus:

And of a male Psammophis sibilans:

Patrick Prévost send me two pictures of a shedding of his Acrochordus arafurae. This snake is known for everting the hemipenes while shedding to allow them to slough along.

And here is a photograph (left) of the shedding of my smallest Psammophylax rhombeatus. Compare it with the ones of the adult (right). There are two protrudings, but there is a large difference between the two. My guess is, that in the left picture a female cloaca is present with the entrance of the egg ducts or of glands, while in the right picture a male is visible, with very clear hemipenes. Look at the pictures above of the male Psammophis sibilans: these are very similar to the ones of the male Psammophylax.

For larger pictures:

Here are all the pictures of the adult Psammophylax rhombeatus. I took the pictures while the shed skin was still wet, apparently the best moment to do it.

 

And some photographs of the shedding of the smallest of my Rhagerhis moilensis, apparently a male:

 

 


Scale counts, ventral and subcaudal, for three snake species

Only for animals of which the gender was proven. This means museum specimens, described in litterature, or trusted reports of snake keepers.

If you have more data, please send them to us.

Rhamphiophis oxyrhynchus

Chirio&Ineich, 1991: "Chez cette espèce, le nombre cumulé de ventrales et de sous-caudales est plus élevé chez les femelles (262-288, moyenne 274,6) que chez les mâles (243-278, moyenne 259,4)."

Rhamphiophis rostratus

Scale counts in general

Rhamphiophis oxyrhynchus rostratus: Ventrals: 162-190, subcaudals 91-125 (2)


Scale counts for proven sexes

Source

Ventrals

Subcaudals

 

male

female

male

female

1

182

183

117

111

 

 

 

 

 

Rhamphiophis rubropunctatus

Scale counts in general

Ventrals: 222-241, subcaudals: 148-160 (2)

Scale counts for proven sexes

Source

Ventrals

Subcaudals

 

male

female

male

female

1

239

215

153

142

1

 

217

 

149

3     141 119

Psammophis sibilans

Scale counts in general

P. sibilans sibilans: ventrals: 151-198, subcaudals 78-121 (2)
P. sibilans sibilans. Ventrals: 178-185, subcaudals 90-97 (4)
 

Scale counts for proven sexes

Source

Ventrals

Subcaudals

 

male

female

male

female

1

 

157

 

110

0

 

167 (cb2010)

 

95 (cb2010)

0 165   98  
0   161 (cb 2013)   95 (cb 2013)

 

Psammophis crucifer

Sexual dimorphism seems to exist in Psammophis crucifer, according to Cottone and Bauer 2010:
"Sexual size dimorphism.—Female P. crucifer grew to significantly larger sizes than males in all traits with the exception of tail length and subcaudal counts (Table 1). The SSD index for P. crucifer was 0.162, with females averaging 14% longer than males in SVL. Analyses of covariance demonstrated that males had longer tail lengths at the same SVL as females, whereas females had wider heads at the same head length as males...".

This was not the case with Psammophylax rhombeatus rhombeatus: "Male P. r. rhombeatus grew to significantly larger sizes in most mean body traits", but that was all. No difference was found in for instance ventral scale counts or number of subcaudals.

 

Sources

0.
Own counting by me, Ton Steehouder

1.
Bogart 1942
Bogart, C.M. 1942. Snakes Secured by the Snyder East African Expedition in Kenya Colony and Tanganyika Territory. American Museum Novitates, Number 1178, Published by The American Museum Of Natural History. New York City. July 27, 1942.

2.
Pitman
1974.
Pitman, C.R.S., 1974. A Guide to the Snakes of Uganda. 2nd ed., Wheldon & Wesley, Codicote.

3.
Loder 2013
Skip E. Loder. Remark in Facebook group Rear Fanged and Oddball Colubrids, on November 3, 2013. https://www.facebook.com/groups/1377000609191408/

4.
Loveridge 1955
On snakes Collected in the Anglo-Egyptian Sudan by J.S. Owen, Esq. Museum of Comparative Zoology, Cambridge, Massachusetts, 1955.