I have never incubated above this temperature (32 deg. C.) but on occasions, such as power supply strikes, the temperature has fallen below the desired minimum (as low as 24 deg. C.) for short periods of time without any damage to the eggs.
One point of interest in regards to incubation temperatures was an experience with a clutch of Sand Goanna Varanus gouldii eggs (Barnett 1979). The eggs were laid by a monitor in the care of a friend of mine. We decided to incubate half of the eggs each and the ones incubated by myself using the aforementioned method and temperatures hatched in 169 - 172 days. The other eggs were being incubated at a lower temperature, unfortunately not recorded, but estimated at 24 - 25 deg. C. Only one of the three eggs survived and were not necessarily lost through lack of heating. After 10 weeks of incubation at this lower temperature, the remaining egg was given to me to place in my incubator. This egg hatched in 208 days which was 39 days longer than the ones that I incubated for the full period at 29.5 - 32 deg. C.
REMOVAL OF EGGS FROM CAGE:
I remove the eggs from the cage where they are being laid as soon as possible. Normally the eggs adhere to each other and form a clutch. Fortunately I have been present whilst most of my eggs were being laid and this has made the task much easier. In the case where the eggs have already adhered to each other it is not essential to separate them unless you need to weigh and measure them, need to fit them in a specific container or it is just your choice for incubation.
Within the first 12 hours or so it is not too difficult to separate the eggs. Select the eggs that are easiest to separate, that is, those on the outside of the clutch and those with the least amount of surface area adhered to the other eggs. The key word is 'gently'. If it looks like any of the eggs may be broken, maybe split the clump into several smaller clumps and incubate in this manner.
The majority of eggs are quite soft as they are laid by the female and I prefer to leave them to dry out and 'harden' for approx. 30 minutes before placing them in the hatching containers. This is done in a reasonably warm area. In most cases, if you are going to weigh and measure the eggs, it would take you this amount of time anyway.
I then discard any obviously infertile eggs. Size is really no good indication of this as fertile eggs from the same clutch may vary greatly in size and/or weight. Any that are extremely soft, do not 'harden up' or have the 'non-white' appearance (normally yellow/brown) are discarded. These days I have a candler lamp which illuminates the interior of the egg but generally only confirms what I already know.
It is advisable to keep records (not memory records - they don't work) of clutch sizes, egg measurements, weights, incubation periods etc.
EGGS TO HATCHING CONTAINERS
With the hatching containers prepared with the substrate and moisture, the eggs are now ready to be placed in the containers. I make a shallow seat in the substrate by pressing down with a finger or removing a small amount of substrate from where the individual egg is to be placed. This is to ensure that the eggs remain stable and retain their position through incubation. Eggs, if handled or removed, should not be turned but kept in the same position throughout incubation. The embryo develops very close to the top of the egg in the early stages and movement of this position may result in the loss of the developing animal. The incubator containers are not overcrowded and the eggs are placed so that they are not touching each other although I do not have any specific reason for doing this, it is more out of habit.
The same amount of medium and water is placed in each hatching container whether it be for a clutch of Children's Pythons eggs weighing a total of 200gms or for 3 Black-headed Python eggs weighing a total of 500gms.
RUPTURED EGGS
I have rarely experienced this and all occasions were in the early days when experimentation was part of the chore. This always occurred from over watering or initially a bad incubation media ratio. No doubt some eggs would have been lost from this but some survived looking maybe 50 - 60% larger when they were laid. There comes a point when the pressure becomes too great and the egg simply dies or a weak point in the shell, possibly created when pulling eggs apart, allows some of the content to weep out. In this case I have removed problem eggs into a dry substrate until the massive expansion has subsided. With modern knowledge this should not deteriorate this far. I prefer to have my eggs looking as they were laid or possibly only very slightly larger. If you can see this problem occurring shake any excess moisture from the container lid. Weigh one of the eggs to give an accurate account of whether it is subsiding.
My most notable ruptured egg was that of a Childrens Python egg that split right open and deflated 31 days into incubation with an estimated 24 days to go. Looking at the little pink occupant one would not give it much of a chance of survival. I decided to try and save this egg and experimented with a 'humidicrib' (Barnett 1980). The egg was tied at each corner and suspended in an elevated position in a container in the hatching container. It was treated more or less as a normal egg from that time on and 'hatched' 24 days later. Its whole progress could be witnessed and photographed in the fully opened egg.
HATCHING
When the time for hatching arrives, the young reptiles make cuts in the egg shell with their egg tooth. They may not emerge from the egg immediately and in some cases remain with their head out, or emerging in and out, for several days. The snake will emerge when all or most of its egg food has been absorbed. Do not make a practice of removing reptiles from eggs simply because of impatience. On the odd occasion where it seemed that a problem was existent a reptile has been removed from an egg its umbilical cord tied and cut, antiseptic to the cut area and placed in a sterile container for several days. Some of these died as there was obviously other complications but also some survived.
Once the first of the clutch has broken through its egg, I sometimes make a slit in each of the other eggs in the clutch. This is generally done for some of the more uncommon or valuable species. Usually I attempt to leave most of them alone. If I slit an egg I rip it rather than cut it. By grabbing the top between the thumb and index finger of both hands I find it pretty simple to create a small rip that exposes the contents without doing any damage to the blood vessels etc.
GENERAL
Incubation periods vary from species to species and those I have incubated ranged from around 8 weeks up to 30 weeks. Periods within a certain species may vary and minor variance in incubation temperatures can produce some interesting ranges. When working with a certain species consult a known authority and discuss techniques with them, it makes sense to get it right this year and not have to wait another twelve months. You will no doubt meet or hear about some local experts on incubation. A second opinion never hurts as many of the so-called experts may have not much more knowledge than yourself. Everyone knows how to do it better and some how come up with these new techniques, devices and equipment that are going to change the herpetological world. They, and their equipment, are usually short lived.
After sharing my experiences with you, on incubation, I hasten to add that when my incubator is full, I put any additional eggs in the hatching containers in a snake cage, after the snake has been removed. They'll hatch there anyway.
ACKNOWLEDGMENTS
Raymond Hoser and Peter Comber discussed parts of earlier material published by myself and offered valuable suggestions on the updating of it. David Humfrey scanned the various slides published with this paper.
The three photos below show a Black-headed Python (Aspidites melanocephalus) hatchling. It was manually removed from it's egg after the rest of the clutch had hatched without incident and it was apparent that this one was having some difficulty. The photos show how the umbilical cord was tied off and a liberal amount of betadine (liquid) was applied before the cord was cut, releasing the snake from it's obstruction. The young snake weighed 52 gm while the average for the remainder of the clutch was 91 gm. The remaining egg that was not ingested weighed 23 gm.