Photographic guide to reproductive behaviour in Elaphe dione with notes on courtship rituals. Including a glossary of common terms used when describing breeding behaviour in snakes.
James C. Gillingham (1979) divided the reproductive behaviour of Ratsnakes into a triphasic scheme.
Phase 3. Intromission and coitus begins when intromission is achieved, and ends when hemipenis is retracted from female’s cloaca.
These three stages are generally the same for most colubrid species, but the movement patterns may differ. Species such as those of the Pantherophis obsoletus complex may exhibit courtship biting, whereas the Fox Snake, P. vulpinus exhibits coital biting.
Below is a sequence of photo's of a pair of Dione Ratsnakes from two minutes after the male was introduced to the female until copulation occurred several minutes later. The pair remained together for approx 20 hours.
Not all species will remain locked up for such extended periods. One theory for extended copulation is that the male is guarding the female this may increase the probability that he, if he is the first male to mate her, will sire most, if not all the females offspring. Species that mate for a shorter time and those that are capable of multiple clutches each year, could be accounted for by the fact that males have a higher probability of encountering a receptive female throughout the year, or that predation is more likely for that species in there natural habitat.
When the male entered the females enclosure she immediately raised her tail indicating her receptivity. Before any contact was made with the female, the male seems to contract his muscles around the base of his tail which I've never noticed before with any male ratsnake.
BEGIN TACTILE CHASE
Male approaches female and makes contact with her using his snout, his head and neck are then elevated and placed on the female’s dorsum.
Anteriorly directed movement of the mounted male with chin rubbing to dorsum of female. (tactile-chase)
Duration: Approx 2 minutes
END TACTILE CHASE - BEGIN TACTILE ALIGNMENT
Tail searching, caudocephalic waves, Forward jerking movement of both snakes while male is mounted.(notice the female with her raised tail indicating her willingness to mate.
Copulatory attempts as the male attempts cloacal juxtaposition and insertion of his hemipenis into the females cloaca (tactile-alignment)
Duration: Approx 4 minutes
END TACTILE ALIGNMENT - BEGIN INTROMISSION & COITUS
Copulation (intromission and coitus)
Duration: Approx 20 hours
Notice the swelling behind the females tail which is the engorged hemipenis of the male. Male snakes have two hemipenis which have a series of spine like projections on them (all species are different, which is one barrier to prevent hybridization), which anchors into the females cloaca and positions over the entrance to the oviduct, where the sperm can be directly released.
Glossary of terms used in describing breeding behaviour in snakes:
Caudocephalic waves - A horizontal rhythmic wave like undulation which begins near the vent and ripples forward towards the head, becoming more pronounced as the male moves on top of the female.
Cloacal gaping - Sexual activity occurring in the female, consisting of raising the tail and everting the cloaca indicating her receptiveness to the male
Cloaca - The common chamber into which the genital, urinary and digestive canals release there contents, which opens to the exterior of the vent.
Cloacae - Plural of Cloaca
Copulation - Sexual union also called coition which leads to the fertilization of the egg by the male.
Dorsum - of or relating to the upper surface of an animal (back)
Hemipenis - The copulatory organ of the male snake, they are paired and located within the base of the tail behind the cloaca. They differ in species but generally are covered in a series of spines and/or hooks which help to hold the organ securely in place in the females cloaca during copulation.
Hemipenes - Plural of hemipenis
Intromission - The alignment of the cloacae and insertion of the males hemipenis into the cloaca of the female
Intraspecific - Within a single species.
Interspecific - Between two or more species
Juxtaposition - Aligning side by side
Ritual Combat - Intraspecific rivalry in males during the breeding season, involving two or more participants, in which each attempts to overthrow the other one. Several bouts may be fought, the length of which is species dependant. Not all species perform ritual combat in a bid to win the mating rites of the female, who is usually in close proximity. In the confines of captivity, this behaviour can be fatal, with the stronger of the two males, harassing the weaker to extreme stress and even death. In the wild the weaker will simply crawl off leaving the victor to pursue the female. The Aesculapian Snake, Zamenis longissimus has perhaps the most elaborate display of any of the Ratsnakes where Ritual combat between males is known.
Tactile Alignment (TA) - The behaviour in courting snakes in which the male attempts to position his tail with that of the females so as to bring their cloacae into line.
Tactile Chase (TC) - The behaviour in courting snakes in which the male follows the female and attempts to mate with her. The male closely follows the female often accompanied by frequent tongue flicking. As he becomes excited he repeatedly tries to locate her cloaca with his own (Tactile Alignment) and his movements become spasmodic. If the female is unreceptive or attempts to flee his advances, in some species he may try to restrain her by biting and holding on. If she is receptive then the chase will end with the Tail search copulatory attempt.
Tail search copulatory attempt (TSCA) - The behaviour in courting snakes in which the male attempts to locate the females tail with his own in order to unite their cloacae into line. If she is receptive she may lift her tail in response to his action (Cloacal gaping). If however she isn't receptive, the male may try to raise her tail with his, this action can repeated many times before a successful intromission is achieved. The tail search usually follows the tactile Chase and precedes tactile alignment.
Vent - The opening located on the underside of the body at the beginning of the tail, the external entrance / exit of the cloaca.
Further Analysis of Reproductive Behavior in the Western Fox Snake, Elaphe v. vulpina. James C. Gillingham 1977 Herpetologists' League
Courtship and Copulatory Behavior of the Mexican Milk Snake, Lampropeltis triangulum sinaloae (Colubridae). James C. Gillingham, Charles C. Carpenter, Bruce J. Brecke and James B. Murphy
Reproductive Behavior of the Rat Snakes of Eastern North America, Genus Elaphe. James C. Gillingham Copeia, Vol. 1979, No. 2 (May 18, 1979), pp. 319-331