Chapter 2 of 13 · Ball Python Breeding Guide

Choosing breeders

Disclaimer: I'm not a veterinarian and I don't hold a degree in animal science or animal care. This is a guide I compiled and use for my own ball pythons. For a sick or egg-bound snake, a reptile vet is the authority.

The short version

  • Don't breed a female under 1,500 g. We wait until she is 1,800 g or more and firm.
  • Males can be smaller. About 700 g and eating well is enough.
  • Keep every new snake apart (quarantine) and test it before it meets your other snakes. We do at least 60 days; some vets advise longer.
  • A "possible het" is only a chance. Use a DNA test before you plan around it.
  • Ask which Axanthic line a snake is and get it in writing. Two different lines make normal-colored babies.

Size and age

Females. A vet-reviewed guide puts the minimum at 1,500 g and maturity at about 27 to 31 months [1]. A breeder site gives 1,400–1,600 g and at least 2.5 to 3 years [2]. In a study of 129 breeding females, the animals were about 2 years old and weighed 1,800 ± 200 g [3]. In the wild, females are grown up at about 95 cm long, measured from the nose to the vent (the opening under the tail). Bigger females lay more eggs [4].

Males. Around 700 g and 16 to 18 months [1]; breeders use males from about a year old and "north of 600–700 g" [2]. One large facility paired males over 500 g [5]. The sources differ, but every one of them asks more of the female than the male.

Our practice: females at 1,800 g or more and firm, never under 1,500 g; males at about 700 g and eating well. A borderline female waits a year.

Health before breeding

Breeding puts two snakes in direct contact, often repeatedly, and then puts their babies in other people's homes. A disease in one breeder can reach a whole collection. These are the ones that matter most for ball pythons:

  • Serpentovirus (nidovirus). A respiratory virus. A US study tested ball pythons in 12 collections. About 5% had the virus, and infected pythons often had breathing problems. A German study found about 22% of ball pythons had it, and many showed no signs at all [6][7]. There is no treatment; positive snakes are isolated [7]. Testing is by oral swab PCR [8].
  • Inclusion body disease (reptarenavirus). Spread by body fluids, mating, bites and snake mites. In pythons it causes severe nerve signs, and most die within days or weeks once signs start. It isn't curable, and infected snakes and their offspring shouldn't be sold [9].
  • Ferlavirus (paramyxovirus). Highly contagious, mainly respiratory, with no treatment [9]. Wildlife Health Australia recommends at least 90 days of quarantine for new snakes [10].
  • Cryptosporidium serpentis. A stomach parasite: regurgitation after meals, weight loss, a firm swelling at the stomach. No treatment cures it; vets advise keeping positive snakes strictly apart from the rest of the collection, and a positive snake should never be bred [11][12].

Quarantine. Vets give different lengths. Some say 60–90 days [13]. For nidovirus, some say 3 months or more [6]. For valuable breeding groups, one review says at least 6 months, with a test when the snake arrives and two more tests 4–6 weeks apart [8]. See Quarantine and health in the Care Guide for the setup.

Our practice: every new animal does at least 60 days in quarantine, with a nidovirus swab after day 30, fecal checks, and weekly mite checks. Nothing pairs until quarantine is finished.

For nidovirus, the sources cited in this chapter recommend 90 days or longer [6][8].

Proven or unproven

A proven female has laid a good clutch before; a proven male has sired one. Proven animals cost more and are older, but you know they can do it. A first-time female might lay slugs (infertile eggs), and slug numbers can rise in later years too [3]. Ask the seller for the date, size and fertility of the last clutch.

Know what you're buying

  • Hets. A "100% het" from a visual parent is certain. A "possible het" (66% or 50%) is a chance, not a gene. A DNA test on a shed can confirm many hets before you build plans around them (see Genetics).
  • Lines that don't mix. Some genes come in separate lines that look alike but aren't compatible. Axanthic is the best known: crossing two different Axanthic lines gives normal-colored babies [14]. Ask which line, and get it in writing.
  • Relatedness. Ask where each breeder came from. Brother × sister pairings concentrate any hidden problem.
A man holds the tail of a ball python and gently slides a thin metal probe beside the vent while others watch
A keeper checks whether a ball python is male or female with a thin, smooth sexing probe; only do this after an experienced keeper or vet has shown you how. Photo: Mile High Bug Club, CC BY 2.0 via Flickr.

Records from day one

Give every breeder an ID and a card: source, hatch date, genetics as sold, DNA results, weights, sheds, meals, health tests. During the season the same card holds introductions, locks, follicle sizes, ovulation, pre-lay shed and lay dates. Most of the timings in this guide are only useful if you've written yours down.

Step by step

Bringing in a new breeder:

  1. Check the size. Females at least 1,500 g (we want 1,800 g or more and firm). Males about 700 g and eating well.
  2. Ask the seller where the snake came from, so you know if it's related to your others.
  3. Ask which line its genes are from, and get it in writing.
  4. For a proven animal, ask the date, size and fertility of the last clutch.
  5. Give it an ID and start its record card the day it arrives.
  6. Put it in quarantine for at least 60 days (see Quarantine and health).
  7. During quarantine, do a nidovirus swab after day 30, fecal checks, and weekly mite checks (our practice).
  8. DNA test any possible het you plan to build on.
  9. Pair it only after quarantine is finished.

Sources for this chapter

  1. The Vet Desk (reviewed by Luqman Javed, DVM), When is the best age to breed ball pythons?
  2. Northwest Reptiles (breeder), So you wanna be a ball python breeder
  3. Bertocchi, M. et al. (2018), PLOS ONE 13(6): e0199377, doi:10.1371/journal.pone.0199377
  4. Aubret, F. et al. (2005), sex differences in body size in the ball python, Journal of Herpetology, doi:10.1670/111-02N
  5. Morrill, B. H. et al. (2011), Herpetological Review 42: 226–231, summary at Conservation Evidence
  6. Hoon-Hanks, L. L. et al. (2019), serpentovirus in US captive snakes, Frontiers in Veterinary Science, PDF
  7. Blahak, S. et al. (2020), nidovirus in ball pythons in Germany, Virology Journal 17: 6, PMC6969405
  8. Boon, A. et al. (2023), Ophidian serpentoviruses: a review, Journal of Herpetological Medicine and Surgery, manuscript PDF
  9. Merck Veterinary Manual, Viral diseases of reptiles
  10. Wildlife Health Australia, Ferlavirus in snakes fact sheet (PDF)
  11. Merck Veterinary Manual, Parasitic diseases of reptiles
  12. WikiVet (veterinary teaching wiki), Snake cryptosporidiosis
  13. Mike Corcoran, DVM, DABVP (Reptile and Amphibian), Ethos Veterinary Health, Quarantine recommendations for new reptiles
  14. García-Elfring, A. et al. (2025), VPI Axanthic and gch2, including crosses between Axanthic lines, Animal Genetics 56: e70011, doi:10.1111/age.70011; open preprint at bioRxiv

Last revised October 31, 2026.