Green Tree Pythons have the ability to thermoregulate their eggs, and if your female will brood her eggs, then most of your incubating concerns are solved. Set up a brooding chamber for the female, which may be the same cage she lays the eggs in, or a special chamber you use just for the purpose. All the female needs to successfully incubate her eggs is an ambient temperature of 82-85 F outside the nest box, and moderate relative humidity. I say "moderate" because chondros don’t need excessive humidity when incubating eggs maternally. In fact, excess moisture will kill the eggs very quickly, and very high humidity will escalate the decaying process of any bad eggs, endangering the rest of the clutch. Water dripping down the cage glass or mold growing in the cage or on the wood nest box indicates too high a humidity level. Make sure you measure the temperature outside the nest box, as temps will be warmer inside due to the female generating heat for the eggs, which she does by muscular contractions.
Maternally incubated eggs take 49-51 to hatch. It is a good practice to carefully check inside her coils a few days after laying to make sure the eggs are fertile. Good eggs are milky white, and full looking, whereas slugs appear yellow or brown. As long as they stay dry and don’t begin to smell foul, a slug or two will not hurt the rest of the egg mass. If they start to rot and turn wet, with a distinct bad smell, they must be removed or the female pulled off and the rest of the clutch incubated artificially. For this reason, an incubator should always be set up and ready. Also, the eggs must be artificially incubated if the female will not form up a good "beehive coil" and incubate them herself. A proper coil completely envelops the eggs, with the female's head covering the center (see photo below.) Females properly brooding healthy clutches do not leave the eggs to drink or bask.
I set up hatching eggs in a clear shoe box with slightly damp paper towels on the bottom, in an incubator set to around 84 F. I manually pip unopened eggs on day 49, and any eggs that have not done so on their own within 24 hours of the first ones. If any babies have part of the umbilical cord attached to their belly, do not try to remove it, it will drop off in a few days, and the first shed will heal the spot.
At a point in time not all that long ago, hatching chondro eggs artificially was considered a very difficult proposition, with first-time success being a rarity.
For years the "jar" method, pioneered by Trooper Walsh and Gene Bessette, was the typical artificial setup. While this setup has been used successfully by both Walsh and Bessette and has worked for me, I have found it to be very intolerant of errors, and it is not easily duplicated by inexperienced breeders.
The Jar type incubation setup
Recently, several breeders have described the use of damp vermiculite for incubating chondro eggs, and I have used this method with success. Mix a medium grade of vermiculite with clean water, and squeeze out the excess until the stuff clumps in your hand like a snowball. The eggs are buried slightly in the vermiculite and set up in the incubator at the temperature discussed below.
Moisture may need to be added occasionally during the incubation process, and if the eggs dent in during the early or middle period of incubation, conditions are too dry. It is normal for the eggs to dent in slightly during the final two weeks of incubation. I find it best to make up a batch of new vermiculite when the eggs need more moisture, rather than trying to add water to the tub holding the eggs. Be sure to inspect the undersides of the eggs to make sure they aren't desiccating, and decrease moisture if clear spots develop. Chondro eggs should look full and white, but not tight or stretched.
The vermiculite setup, showing lid opened and thermometer probe.
It is important to switch the eggs over to damp paper towels at hatch time, to prevent the hatchlings from getting covered in damp sticky vermiculite. This can kill them, especially if they ingest it. I place pipped eggs in a clear plastic shoe box lined with damp paper towels, and set the temperature at about 85 degrees.
For details about my use of vermiculite to hatch the 2001 calico eggs,
Most recently, an even easier method adapted by Trooper Walsh has been used with success by first-time breeders and experienced persons alike. Referred to as the "no-substrate" method because the eggs are not in contact with anything, this setup uses standing water to provide humidity. The eggs are placed embryo up in small plastic deli cups, about 6 eggs per cup. The egg cups are then placed on a plastic grid that is suspended above clean water in the bottom of a clear plastic box. Small pieces of PVC pipe are used to suspend the grid. The lid is placed on the clear box, and no ventilation holes are used, other than a small hole in the lid to allow insertion of the thermostat and thermometer probes.
Water substrate setup, showing egg cups, plastic grid, water, pvc pipe holding up the grid above water, and the thermostat and thermometer probes in contact with the eggs. The mercury lab grade thermometer in the foreground is used by the author to calibrate all his other devices.
During the final week, the eggs begin emitting moisture, and must not be allowed to set in the water that will collect in the bottom of the deli cups. Increase the ventilation to deal with this. Remove the eggs and set them up in a hatch tub as described in the vermiculite section. The eggs in the photo above were manually pipped on day 49 and the young emerged over the next few days. They averaged 12 grams in weight.
I like this method very much because it eliminates an important variable, namely how much moisture is present. There is no measuring or guesswork, as is needed when using vermiculite. Also, this method is very low maintenance in nature...there is no need to add water, and experimentation has shown there is no need to open the egg box for ventilation. This setup can therefore be left as is for days, except for making the recommended temperature changes outlined below.
Some breeders use one steady temperature throughout incubation, but I prefer to use the regimen developed years ago by Ophiological Services and based on the careful monitoring of multiple brooding females. I use Celcius to calculate temps, but I have given the Fahrenheit equivalents here too. The regimen is:
30.5 (86.9) for the first week
31.5 (88.7) for the middle five weeks
29.5 (85) for the final week
Make changes gradually. It is important to note that these are egg surface temps, not air temps. Also, properly calibrated and consistent equipment must be used to monitor eggs. I use an Atkins thermocouple probe thermometer that has been calibrated to within 0.01 of a degree C using an ice water slurry. I regularly experience 49 day hatches using this regimen and the Atkins thermometer.