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The information on this page, comes from my own breeding, done with my own animals, unless otherwise stated.

Temperature Sex Determination (TSD)

     Temperature Sex Determination experiments have taken place in reptiles, where a clutch of eggs are separated into two groups, and each group is incubated at different temperatures, and the resulting hatchlings sex is recorded. The people that argue that TSD does not take place in snakes, have not provided me with any legitimate info of these experiments being done on snakes specifically. Only studies on lizards and turtles, where later they mention, they do not "think" TSD takes place in snakes.

     If experiments with snakes, have taken place, as with lizards and turtles, and the results show temperature does not effect snake eggs, then TSD may not be taking place during the incubation period of the snake eggs. But, that does not prove that TSD is not taking place during conception, or during the formation of the eggs in the female.


     I found one paper by Wei Guo Du and Xiang Ji  titled "The Effects of Incubation Temperature On Hatching Success, Embryonic Use of Energy and Hatchling Morphology in the Stripe-tailed Ratsnake Elaphe taeniura", found in the publication, "Asiatic Herpetological Research, Vol. 11 2008, pp.2430". Below chart below is copied from that paper.  (I added the degrees F).

Here is a link to that paper. http://www.asiatic-herpetological.org/Archive/Volume%2011/11_05.pdf 

Temp (C - F) Duration of Incubation Hatching Success Sex Ratio  (♂♂/♀♀)
22     71.6 101.71.3 50.0 (6/12) 4.2
24     75.2 86.00.6 78.1 (25/32) 13.12
27     80.6 66.30.7 79.2 (19/24) 6.13

          30     86

53.90.4 79.3 (23/29) 12.11
32     89.6 50.50.5 41.2 (7/17) 5.2

     As you can see in the chart above, concerning TSD in an Elaphe specie, the chart shows that the sex ratio of the clutches were male heavy at the extreme high and low temperatures. The ratio was basically even at the next highest and lowest temps, and more females were produced at the mid-range temp.

     Our own breeding trials show that, during the keeping, breeding, formation of eggs in the females, and incubation of the eggs, at lower temps, can result in clutches with a higher ratio of females, though we never incubated eggs at temps lower than 26.6 C (80 F).



Our Results

Equatorial Spitting Cobras  (Naja sumatrana)

     Some people say Temps have no influence on the sex of snake eggs, others say they have experienced TSD themselves with their own snakes.  One person told me, that you "must" split the clutch into 2 even groups and then incubate them at different temps, and do this over several breeding seasons, with different pairs of snakes, or you can not prove anything. I don't think splitting a clutch into 2 groups makes any sense. What if the sex was determined at conception, or later, during the formation of the eggs in the female? It could be that the temps in which she is being kept, has influenced the sex. That would still be considered "Temperature Sex Determination".  Would it not?

     Initially, we were keeping our Snake Room at 85 - 86 degrees (29.4 - 30 Celsius) at all times. We were just collectors of exotic venomous snakes, mostly Cobras, but also some Oz/PNG Elapids, and a Nile Crocodile. The first specie of snake we ever bred were Eastern (Common) Brown Snakes. We bred them in Jan. 2003 and Jan. 2005, but never could get them to eat, and they didn't survive. They were extremely small.  Smaller than any Corn Snake hatchling we've ever seen. Also, in Jan. 2005, we bred Sri Lankan Spectacled Cobras, without cooling them. The snakes were kept at 85 - 86 degrees (29.4 - 30 Celsius). They bred at those temps. The eggs formed in the female, were laid, and were incubated at those temps.  There was a 12 . 5 sex ratio.  That is 12 males and 5 females for those of you that didn't know.

     We moved to Florida in Sept. 2005, and then we got more into breeding. We were still keeping the Hot Room at 85 - 86 degrees, but we started cooling the snakes before breeding. After cooling, we slowly warmed the room back up to 85 - 86 degrees, and after a meal, we put the snakes together. The following information is on our original pair of Yellow Phase Equatorial Spitting Cobras (Naja sumatrana), as we have bred the same pair together since 2006, and kept exceptional records.

     The first year they were kept at 85 - 86 degrees (29.4 - 30 Celsius), all year, then cooled, and then warmed back up to the same temps. They were introduced, and they bred at those temps. The eggs formed in the female at those temps. The eggs were incubated at those temps. We incubated the eggs in a 9.75" clear plastic deli cup with the holes in sides of the cup covered with tape, and just 7- 8 pinholes in the deli cup lid, so that no bugs could get in, but the eggs can breath.  A little condensation forms on the inside of the deli cups. We used a 50/50 mix of vermiculite/water by weight, and left them sitting on a shelf in our Hot Room, at 85 - 86 degrees. After 64 days, 6 of the 7 eggs hatched and there was a 5.1 sex ratio.  The 7th egg did not hatch.

     After we saw the 5.1 ratio that first year, we talked to some friends about it. They suggested we lower the temps. We immediately lowered the temps that we kept the snakes at throughout the year. Then we did everything exactly the same, with the same pair of snakes at the new, lower temps. The third year, we lowered the temps more, but only slightly, and did everything else the same.

     The chart below shows that temps can/do have an effect on the sex of the offspring, other than the eggs taking longer to hatch at lower temps. If you split the eggs of one clutch, into 2 groups, and the sex has already been determined by temps or other factors during their formation in the female, then your test is showing you nothing. But, when you breed the exact same pair of snakes, over several years, and everything else is the same, except temperature, and you continuously get less males and more females at the lower temperature range, then TSD (Temperature Sex Determination) is taking place.

     **  In July 2008, we finished building my new Snake Room. It was built inside a steel building, with 2x4 walls, 2x6 ceiling joists, and it is insulated just like a house would be. We put Luan on the inside walls. It was then painted white. We have a good sized A/C unit for cooling, and two oil-filled electric heaters, each controlled by separate Johnson Controls, on separate breakers, and 4 ceiling fans circulating the air. Shortly after it was finished, and the smell of paint was gone, we moved the adult snakes into the room. Shortly after that, mold started to grow on the walls and ceiling. We washed it off, but it grew back. We purchased a dehumidifier and it solved the problem. But, maybe too late, as we lost a few, otherwise healthy, adult Corn Snakes and King Snakes, and then a few months later during Brumation, we lost our male breeder N. siamensis, our male breeder N. melanoleuca, and a CB'06 female N. sumatrana. The temps never went below 55 F (13 C). and everything was healthy. The N. siamensis and N. melanoleuca may have been old animals, but the N. sumatrana was produced here, was young and healthy.

     Before moving the adult snakes to the new Snake Room, they were in bedrooms in our house, and we were using the same type heaters, but using Helix Controls instead of Johnson Controls. The humidity was naturally much lower, so we didn't need a dehumidifier in the house. Maybe the temps in the new Snake Room were not as low as we thought, since we were was using new heat controls and different A/C unit. Maybe the very high humidity or mold had some effect, maybe not, but as you can see, we did everything else the same, but that year we got more males than females. That was also the first year that the eggs were laid in the new Snake Room, and incubated in the same room in my house as the 3 prior years.

     In 2010, we did everything the same as in 2009, but the Temperature and Humidity remained more constant, ie: no radical rise in humidity. The dehumidifier has worked very well. The same two adults were bred again, and they produced 10 eggs. The largest clutch thus far. One egg went bad quickly, and the other 9 started hatching out after 74 days, and finished hatching after 75 days. The sex ratio is 4.5, once again, showing a higher number of females, at the lower temps.

     In 2011, the same pair bred, and they produced only 4 eggs. After 76 days at 80 - 82 F (26.6 - 27.7 C), 3 of the 4 eggs hatched, and the ratio was 1.2. Not much can be determined from such a small clutch.

     In 2012, the same pair bred again, and this year they produced 9 eggs. After 72 days at 81 - 83 F (27.2 - 28.3 C), all 9 eggs hatched, and the ratio was 4.5.

     **  See in the chart below were the problems with humidity and mold may have caused abnormal results.

Naja sumatrana  SumY-001-AD-F

.....Year..... ..........Temperature.......... ...Lay.Date... ..#.Eggs.. #.Infertile.Eggs ..Hatch.Date.. Incubation.Period #/Sex.Hatchlings
2006 85 - 86 F   (29.4 - 30.0 C) April 21 7 1 June 24-28 64 Days 5 . 1
2007 81 - 83 F   (27.2 . 28.3 C) April 18 5 1 July 1-2 74 Days 2 . 2
2008 80 - 82 F   (26.6 - 27.7 C) April 18 6 0 July 5-7 78 Days 2 . 4
**  2009     80 - 83 F   (26.6 - 28.3 C) April 20 8 0 July 4-6 75 Days 6 . 2
2010 80 - 83 F   (26.6 - 28.3 C) April 26 10 1 July 9-10 74 Days 4 . 5
2011 80 - 82 F   (26.6 - 27.7 C) March 29 4 1 June 13 76 Days 2 . 1

*** 2012

81 - 83 F   (27.2 - 28.3 C) March 31 9 0 June 11 72 Days 4 . 5

     ***  All 9 eggs hatched, but one female died within an hour of hatching. She was counted in the sex ratio of 4.5, but only 4.4 are alive. I showed this to account for all know sexes.

     Important Note: In the above and below charts, where it shows temperature, the temps you see are the temps the snakes were kept at during the year before breeding, and the temps at which they bred. The eggs formed in the females at that same temp, and the eggs were incubated at that same temp.



Our Results

Indochinese Spitting Cobras  (Naja siamensis)

    The Chart below, shows that in 2006 and 2007, the results from breeding the exact same pair of Indochinese (Black & White) Spitting Cobras (Naja siamensis).  As you can see, at the lower temperature in 2007, they produced a lower ratio of males and a higher ratio of females, and again took slightly longer to hatch.

   *  In 2009, I bred a different, younger male, to the same female from the 2006 and 2007 breeding season, because as stated previously, my main breeder male died during Brumation. I've added the info below, but since it was a different male, the data may not completely apply.

     In 2011, the same female was bred to yet another different male. 

Naja siamensis  Sia-001-99-F

.....Year..... ..........Temperature.......... ...Lay.Date... ..#.Eggs.. #.Infertile.Eggs ..Hatch.Date.. Incubation.Period #/Sex.Hatchlings
2006 85 - 86 F   (29.4 - 30.0 C) March 31 20 5 May 26-28 56

        12 . 3


81 - 83 F   (27.2 . 28.3 C) April 9 21 1 June 10-12 62

 7 . 13

*  2009     80 - 83 F   (26.6 - 28.3 C) April 8 29 0 June 12-15 65

        18 . 11

2011 80 - 82 F   (26.6 - 27.7 C) April 17 27 1 June 22-24


14 . 12



Our Results

Central Asian Cobra  (Naja oxiana)

      In 2008, we bred Central Asian (Russian) Cobras for the first time. This species used to be bred with some regularity by at least one man in Europe, but you rarely see them now.  As adults, they are not one of the more beautiful species of Cobra, but they are in the top 5 when it comes to personality. We first introduced the female to the male on 02/18/08. We saw them breeding on 3/15/08 and 3/21/08, and she laid 8 eggs on 5/2/08. They probably bred before we saw them, because the eggs were laid in only 48 days.  Four of the eggs were infertile. We incubated the 4 good eggs, and the results are below.

     In 2011, the same pair of Naja oxiana finally bred again. She produced 11 eggs, but only 3 made it to hatching.

     In 2012, the same pair bred again, and she produced 8 eggs and again only 3 hatched out. We recently found out that the female, whom we were guessing was a CB'02, was actually brought into the USA in 1999 or 2000, making her possibly 14 years old or older.

     Also in 2012, the two daughters produced here in 2008 both bred. Details below.

  ** In the 2014 season, we cooled our snakes longer, and colder than usual. We started cooling on Oct. 1. We took a week to get down to 65 degrees. The snakes stayed at 65 degrees until Nov. 24. Then we took a week to raise the temp back up to . All 3 females bred and produced more eggs than ever before.

Naja oxiana Oxi-002-99-F

.....Year..... ..........Temperature.......... ...Lay.Date... ..#.Eggs.. #.Infertile.Eggs ..Hatch.Date.. Incubation.Period #/Sex.Hatchlings


80 - 82 F   (26.6 - 27.7 C) May 2 8 4 July 3 63 2 . 2
2011 80 - 81 F   (26.6 - 27.2 C) April 8 11 8 June 11 64 2 . 1
2012 81 - 83 F   (27.2 - 28.3 C) April 25 8 5 June 22 58 1 . 2

82 - 83 F   (27.7 - 28.3 C)

March 30 12 1 May 29 59 8 . 3

Results of two CB'08 females bred to the same male

.....Year..... ..........Temperature.......... ...Lay.Date... ..#.Eggs.. #.Infertile.Eggs ..Hatch.Date.. Incubation.Period #/Sex.Hatchlings
2012 81 - 83 F   (27.2 - 28.3 C) May 2 9 0 June 28 57 4 . 3
2012 81 - 83 F   (27.2 - 28.3 C) May 4 10 1 July 1 58 4 . 5


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