Keywords: eggs - cannibalism
Date of publication: June 22, 2011, based on an original article from 1994.
Since 1983 I have bred irregularly snakes of the genus Psammophis: fast, day-active hunters, mostly originating from Africa. Of my experiences with these snakes and the breeding of them I have reported regularly in some Dutch magazines. In this article, originating in 1995, I discuss some interesting new experiences.
In 1983, I bred Psammophis subtaeniatus for the first time. I
reported about this extensively in an article that was published in Lacerta
and in Litteratura Serpentium. In this article I devoted a paragraph to
the incubation method. In my early days as snake breeder I incubated the eggs on a layer of moist
aquarium filter wadding, not covered. The eggs developed after some time a sort
of ‘belly’, probably because they absorbed water from the substrate. The next
clutch was incubated in moist sand, with lumps of moist sand on top, in a
plastic box with small holes for ventilation, and placed in a incubator.
This last incubating method worked so well (the temperature in the sand remained pretty even, the eggs didn’t get dirty and the hatchlings were directly visible) that I remained using this methode in the years to follow, especially with eggs of Malpolon and Psammophis.
The only change was that I started to use moist wood shavings instead of sand, which worked equally well and had the advantage of being light and cheap.
During the first years, I was also very careful in keeping a constant temperature around the eggs: between 27º and 30ºC, and I started to be worrisome if by circumstance the eggs would cool off somewhat. Over the years I became less careful though, without a noticeable difference.
Remarkably, the volume of the eggs of Psammophis increased heavily by the absorption of moist in the first weeks, just like the eggs of most Elaphe- and Lampropeltis species. The Psammophis I breeded originate from more arid habitats. The eggs of the related species of Malpolon did not or hardly absorb moist.
The data in table 1 have been published earlier (Steehouder, 1988). As you can see, some eggs gained approx. 50% of their weight!
In short: the good snake holder ensures that the eggs can develop in a suitable substrate, can sufficiently absorb moist, and remain within a suitable range of temperature for its type.
In 1994, the female that breeded successfully in 1992 mated with several
males among Psammophis sibilans which the same male Psammophis
subtaeniatus sudanensis (?) with whom she had been mating in 1992.
In the beginning of June all Psammophis and Malpolon were temporarily moved to the home of a friend as I was moving to another home and the vivaria had to be taken apart. The sand snakes were moved in their own hiding boxes, filled with word shavings, wherein they were used to retreat each evening – very practically in this case: I only had to put the lid on the box, tape it and move all.
These boxes were being used during their stay, and again during and after transport (at the end of July) at the new address. Summer was hot, the temperature in my new snake room was as high as 33̊ C during the hottest period, and lowered to about 28ºC during the night. There were some nights and days that were cooler, but only some.
I was busy rebuilding and decorating, and didn’t have more than the necessary attention for my snakes.
On August 8 I was astonished to notice a dead hatchling, hanging over a branch. I took it away and removed the hiding box – which was the predictable cause of a fierce hunting event for excaped sandsnakes and a bleading wrist – and discovered that the hatchling was about 30 cm long, and looked stout and healthy, apart from being dead.
On about a quarter of its length, near the heart area, the hatchling showed lengthwise damage markings, clearly caused by its being bitten by one of the older animals. At the underside it showed signs of a hemorrhage.
Probably the aggressor had been disturbed in the execution of his evil plans by my entyering the room and had left his prey hanging over the branch.
In the hiding box, among the wood shavings, we found seven eggs of approximately the same size as the ones of the same female in the past directly after they were laid. The scales were brittle and heavily sunken (a cross section would be a sort of quadrangle). There had clearly not been any absorption of moist (which hadn’t been present) but pecularly they were not all dried up too. The eggs must have been lid in the first week of June. All seven had hatched, but six hatchling were lost and – as I presume – been swallowed by the adult snakes. Escape from the vivarium was very unlikely: there was not enough space between the glass panels.
The remarkable aspect of this case is in the first place that the eggs of
these snakes apparently absorb moisture during the incubation, but that this is
clearly not a necessary condition for a healthy development of the hatchlings.
In this case there had been no absorption. Relative moisture of surrounding air
had not been high enough to even theoretically compensate: at any rate not above
In plain statement it could be said that eggs of these species can apparently hatch successfully even if you simply leave them somewhere in the terrarium, and that my earlier concern as a starting snake keeper about the welfare of the eggs, seems to be a little comical.
A second remarkable fact is that the hatchlings (at least one of them, but presumably all) were killed by the parents. Cannibalism in snakes is not abnormal. In 2010 a juvenile P. sibilans in my possession swallowed two of his brothers/sisters. The reaction of snakes of this species when I show them small other snakes, indicates that smaller snakes are probably considered as prey animals.
The problem is that we don’t know how many cases of conspecific cannibalism there are in the wild. Factors of captivity can play a role in the phenomenon of snakes hunting each other, but we cannot know exactly to which extend.
Petzold (1984) discriminates between two forms of cannibalism: real and pseudo-cannibalism. The last form is evoked by unusual circumstances. He distinguishes two subforms: overpopulation cannibalism, caused by the forced presence of (too many) conspecifics that cannot be avoided, and prey envy cannibalism. In the first case, the permanent unavoidable presence of an inmate can be the cause of a sudden case of cannibalism.
In the terrarium the chance would be that sudden movements of other snakes evoke hunting behavior of their inmates. This would be an explanation of cases of cannibalism in which larger conspecific animals are involved, such as in the case Tom Vos described: one adult P. sibilans was killed in absence of prey.
In the wild, the encounter of adult and juvenile snakes of the same species will be a lot less probable than in captivity.
Cornelius (Kees) de Haan, whom I always consult in curious questions or mysterious cases with Psammophines, wrote me that he has had a similar experience with six eggs of P. schokari: all eggs were found empty and dried up in the terrarium, all of the hatchlings had disappeared, and as an escape can be excluded as a possibility here too, the adult animals must have consumed them.
Petzold, Hans-Günter, 1984. Aufgaben und Probleme bei der Erforschung
der Lebensausserungen der Niederen Amnioten (Reptilien). Berliner Tierpark Buch
Steehouder, A.M., 1984. 'Herhaalde succesvolle kweek met de 'zandrenslang' Psammophis subtaeniatus sudanensis en opmerkingen over het poetsgedrag.' Litteratura Serpentium Vol.4 (3/4):94-108 (ook in Lacerta 42 (10/11):194-200).
Ton Steehouder, 1988. 'Een nieuwe generatie zandslangen.' Het Terrarium 5(10), mei 1988.
Ton Steehouder, 1992. 'Een geslaagde kruising van Psammophis sibilans en Psammophis subtaeniatus in het terrarium.' Litteratura Serpentium 12(5):134-146 (okt. 1992).
Ton Steehouder, 1993. 'Over het verschijnsel kannibalisme bij slangen.' Het Terrarium 11(3):50-59.