Short of obtaining veterinary assistance, the best way to know if your python is holding fertile eggs is by watching for a suite of traits that gravid pythons commonly exhibit. While most of these clues are not infallible, the observation of ovulation guarantees that your python will deposit eggs in the near future. Other clues that are consistent with, but not necessarily indicative of, gravidity include changes in your animal's body proportions and distinctive postures.
The easiest way to collect empirical evidence that your snake is gravid, or pregnant, is to visit your veterinarian, who can take X-rays of your pet or use an ultrasound to visualize her reproductive organs. Gravid females have clearly visible ova located in the oviducts; those without such are not gravid. However, carting your snake to the vet – potentially several times – is stressful and costly. Many experienced breeders watch for other signs that either confirm or suggest that python eggs are eminent.
Body Proportion Changes
As the ova begin swelling inside the female's ovaries, they end up taking up more space, thereby making the female look thicker than normal. Normally, this thickening is visible before breeding activity starts, but it can begin after the snakes begin mating. This is most pronounced between the snake's midpoint and vent. Females must mobilize fat stores to help nourish the eggs, which may cause their tails to lose a small amount of weight, also more noticeable near the snake's vent. The heads of some species – notably green tree pythons (Morelia viridis) – become flattened in appearance when the snakes become gravid.
Some pythons change colors as part of their reproductive cycle. Ball pythons (Python regius) may develop a stronger contrast between their light and dark pattern elements, while female green tree pythons often become pale blue during their reproductive cycle. Carpet pythons (Morelia spilota) may become darker as they approach parturition. However, none of these color changes conclusively indicate that a snake is gravid.
Unusual Postures and Behavioral Changes
Some gravid snakes alter their behaviors in obvious ways. Many gravid snakes appear uncomfortable and adjust their position frequently. Some gravid females may pace their cages repeatedly, especially when nearing the time for egg deposition. Females usually refuse food once they are gravid. Females may seek out cooler areas in the cage around the time of ovulation but seek out warmer areas in the cage at other times. To help accelerate the development of the eggs, some females lay in inverted postures while gravid, thereby placing the eggs closer to the heat source.
Your Best Bet: Observing Ovulation
When pythons ovulate, they release all of the eggs in a given ovary simultaneously. Sometimes they release the eggs from one ovary at a time, but in other cases they release all of their ova at the same time. The release of these ova and the process of moving them into the oviducts cause a distinct and dramatic mid-body swelling. This is much different from the gradual and somewhat subtle thickening that occurs due to the growth of the eggs.
Novices can become quite startled upon seeing ovulation the first time; it can appear as though your snake swallowed a football. The bulge lasts for up to about 24 hours, after which your snake will return to her normal proportions. If you witness ovulation, you can be certain that eggs are en route, as the female has no internal mechanism for reabsorbing ovulated eggs.