Eggs and incubation

The short version

• A clutch is usually about 6 to 7 eggs. Small, yellowish eggs are slugs, which won't hatch.
• Don't turn or roll the eggs. Mark the top of each one with a soft pencil before you move them.
• Keep the temperature steady and check it on a second thermometer next to the eggs. We plan to run 88–89 °F. Running too hot causes more defects than running a little cool.
• Keep the air very humid, but keep the eggs from getting wet.
• Eggs take about 2 months to hatch.

The clutch

• Size: a facility that logged 5,344 eggs from 783 clutches averaged 7 eggs per clutch and hatched 81% of them [1]. The 129-female study counted 6.3 ± 2.3 fertile eggs plus 1 or 2 slugs per clutch on average [2].
• Eggs: about 85 g each; the whole clutch about 32% of the female's weight before laying [3].
• Slugs (infertile eggs) are smaller and yellowish [2].
• Stuck together: fertile eggs often stick in a cluster. Most breeders leave the cluster whole and move it as one piece; pulling eggs apart can tear the shells.

Don't turn the eggs

Soon after laying, a snake embryo attaches to the inside of the shell, usually near the top. In a study of water snakes, turned eggs and unturned eggs hatched at about the same rate. But afterward, 37.5% of the babies from turned eggs died, against only 4.5% from unturned eggs. The authors recommend incubating eggs in the position they were laid [5].

Mother or incubator?

Maternal incubation. A female coils around her clutch for about two months. When she coils around the eggs, it barely changes their temperature, but it does a lot to stop them drying out. Eggs she sat on gave bigger, more active babies [6]. In one study, all the eggs were at about 29 °C (84 °F). Eggs left with the female hatched at 58–59 days. Eggs taken away hatched at 71–76 days. Both groups lost the same share of eggs [3]. A female can't cover an oversized clutch, and the eggs she can't reach dry out [7]. If you go this way, keep the enclosure in the low to mid 80s °F with humidity around 80% [8], and expect her not to eat until the eggs hatch [3].

Artificial incubation lets the female start eating and recovering sooner, and is what most breeders do.

Choosing an incubator

What matters is a temperature that stays put. One breeder guide says to keep it within 0.5 to 1 °F of the set point [15].

• Cooled lab incubators (compressor-cooled) hold a set point within about ±0.2–0.5 °C and can cool as well as heat [9]. They handle a hot summer room, which is when eggs are incubating.
• Heat-only reptile incubators work well in a stable room, but can't cool; a summer heat spike pushes them over. Their built-in sensors may not read egg-level temperature, so manufacturers say to add a second thermometer at egg height [10].
• Styrofoam still-air incubators depend heavily on room temperature; a room that swings 10 °F or more changes the inside temperature [11]. In one keeper's side-by-side test of three incubators, one ran about 2 °F cooler at the egg box than its display showed [12].
• Converted wine coolers with a good thermostat are a common keeper build [13].

Whatever you use: a quality proportional thermostat, a second independent thermometer next to the eggs [10], and a test run with the empty incubator before eggs go in. One maker says at least half a day [11]; a longer run shows how it copes with the room warming and cooling.

Temperature

• The 783-clutch facility incubated at 30.9 to 31.7 °C (87.6 to 89.1 °F) [1].
• Breeders run 86–92 °F, most at about 88–90 °F; eggs at 88–89 °F hatch 3 to 5 days later than at 91–92 °F [14][15]. Hobby sources say running too hot causes more defects than running slightly cool, so they lean toward the cooler end [23].
• Cooler incubation takes longer: 63 days at 30.5 °C (87 °F) for one clutch in an older study, and 71 to 76 days at 29–30 °C (84–86 °F) in another [16][3].
• No study ties incubation temperature to kinks in ball pythons specifically. In pine snakes, abnormalities appeared only in cold incubation, and hatching success fell at 32 °C [17].

Humidity and substrate

The egg box needs very humid air without wet eggs.

• Vermiculite or perlite with water. A common mix is equal weights of vermiculite and water, about 3 in deep [8][15]. The 783-clutch facility used perlite and vermiculite 1:2 by volume, moistened with water [1].
• Pre-mixed substrates need no mixing; one maker says to just pour it in [18].
• Suspended incubation (eggs on a grid over water, not touching any substrate) is used by some keepers [19]. With no substrate to buffer it, humidity needs closer watching [25]. Make sure the grid is secure so a hatchling can't end up in the water.
• Don't let condensation drip on the eggs: tilt the lid as you open it, and set the box so drops run to the edges [4].
• Humidity targets differ: about 90% in one breeder guide, 80–100% in another [14][15].

Checking the eggs

• Candling. In a dark room, shine a cool light against the shell. A fertile egg shows blood vessels, visible from about a week after laying in some reports and around day 14 in others; an egg that is still clear at 2–3 weeks is unlikely to hatch [20][21]. Don't lift or roll the egg to do it, and use a light that doesn't get hot.
• Dents. Collapse in the first few weeks means the eggs are drying out: add a little water to the substrate, not to the eggs [8][4]. Dents in the last week or so are normal, as the baby uses up what is in the egg [24].
• Swollen, bloated eggs mean too wet [20][4].
• Mold. Sources disagree. One article says patches on the shell are mostly harmless and best left alone; a substrate maker says moldy eggs are best removed, unless they are stuck in a cluster [20][18]. A clearly dead, moldy slug can come out; a fertile egg stuck to a moldy one stays.

How long

59.4 ± 3.7 days from laying to hatching in one study [22]; breeders commonly see 55–60, and 65 isn't unusual [15].

Step by step

Incubating a clutch:

1. Before the season, do a test run with the empty incubator (we run it two weeks), with a second thermometer at egg height.
2. Set up the egg box with damp vermiculite or perlite. A common mix is equal weights of vermiculite and water, about 3 in deep.
3. Don't let condensation drip on the eggs: tilt the lid as you open it, and set the box so drops run to the edges.
4. When she lays, mark the top of each egg with a soft pencil before anything moves.
5. Move a stuck-together cluster as one piece. Don't pull eggs apart, and don't turn them.
6. Set the eggs in the egg box in the position they were laid, pencil mark up.
7. Check the temperature every day on the second thermometer.
8. Candle the eggs with a cool light, without lifting or rolling them.
9. Watch for dents in the first few weeks (add a little water to the substrate, not the eggs) and for swollen, bloated eggs (too wet).
10. Expect hatching about 2 months after laying.

Sources for this chapter

1. Morrill, B. H. et al. (2011), Herpetological Review 42: 226–231, summary at Conservation Evidence
2. Bertocchi, M. et al. (2018), PLOS ONE 13(6): e0199377, doi:10.1371/journal.pone.0199377
3. Ellis, T. M. and Chappell, M. A. (1987), Journal of Comparative Physiology B 157: 393–402, PDF
4. FurryCritter, Incubation moisture levels (hobby site)
5. Aubret, F., Blanvillain, G. and Kok, P. J. R. (2015), egg turning in snakes, Scientific Reports 5: 13385, PMC4543940
6. Aubret, F. et al. (2005), maternal brooding in ball pythons, Evolutionary Ecology Research 7: 743–758, abstract (archived)
7. Aubret, F. et al. (2003), clutch size and brooding in ball pythons, Biological Journal of the Linnean Society 78: 263, summary
8. Reptiles magazine (2006), Python egg incubation
9. PHCbi (Panasonic), MIR-154 cooled incubator specifications (manufacturer)
10. Zoo Med ReptiBator, product specifications via Josh's Frogs (retailer copy of manufacturer text)
11. GQF Hova-Bator, instructions (manufacturer, PDF)
12. GeckoTime (2015), A tale of three incubators (keeper blog)
13. MorphMarket Community, Good incubator recommendations (keeper forum)
14. Northwest Reptiles (breeder), So you wanna be a ball python breeder
15. MoreReptiles (vet-reviewed), Ball python egg incubation
16. van Mierop, L. H. S. and Bessette, S. M. (1981), summary at Conservation Evidence
17. Burger, J. et al. (1987), incubation temperature in pine snakes, PDF
18. HatchRite instructions via LLLReptile (retailer copy of manufacturer text)
19. MorphMarket Community, Incubation methods (keeper forum)
20. Reptiles magazine, Candling and egg problems
21. Incubator Warehouse, Reptile egg candling (retailer)
22. University of Pisa veterinary thesis (2024), 48 females (abstract), etd.adm.unipi.it
23. FurryCritter, Deformed hatchlings (hobby site)
24. MorphMarket Community, Incubation eggs denting (keeper forum)
25. FurryCritter, Incubation medium (hobby site)