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Incubating Reptile Eggs – A Simple Method of Monitoring Moisture Content

The moisture content of the substrate upon which reptile eggs are incubated is a critical factor in hatching success. While certain hardy species fare well under the much-promoted technique of “squeezing water from the substrate until it barely sticks together”, many eggs require closer attention to detail.

Equipment Needed
I would like to pass along a method that I have used for hundreds of species, both in zoos and in my own collection. All that is required by way of measuring devices is a simple gram scale and a graduated cylinder (marked off in milliliters). Fortunately for me and other mathematically impaired herpers, calculations are simple – it turns out that 1 milliliter of water weighs 1 gram.

The Technique
First, determine the moisture level required by the eggs that you are incubating (please write in if you need help with this). Then, using the gram scale, weigh out enough substrate contain the eggs. You can now easily set up a ratio of, for example, 1 part substrate to 1 part water, by measuring, in the graduated cylinder, a corresponding volume of water. So, 10 milliliters of water added to 10 grams of vermiculite provides a 1:1 ratio (1:1 works well for many, but not all, reptiles).

Place the eggs (1/2 buried for most reptiles) and moistened substrate into a sealed container, weigh the container and record the weight (and date) on the cover. The cover should not be ventilated – for most reptile eggs, a once- daily check provides enough oxygen exchange (ventilation may need to be increased for large numbers of eggs once hatching time nears – please write in if unsure).

Keeping Track of Moisture Loss
Weigh the container weekly – any weight loss will be the result of evaporation, and should be made up by adding an appropriate volume of water to the substrate. For example, if the container weighs ½ gram less than the previous week, add ½ ml. of water.

Please look for future articles on egg incubation. Until then, please write in with your questions and comments. Thanks, Frank

The abstract of an interesting article on the conservation of moisture in reptile eggs is posted at:
http://www.springerlink.com/content/4032m356l66k66u3/

26 comments

  1. avatar

    Hello Frank,

    Well, you were quite correct! Yesterday I found a clump of 5 eggs in the laybox! I went ahead and moved them into a plastic container with perlite(moistened to the point where it was wet enough to mold like a snowball, but when squeezed hard no more than a drop or two of water would come out.

    I recall from the previous thread you reported some problems with mold and that this species may need it a bit dryer? The eggs all look nice and white right now.

    ~Joseph

  2. avatar

    Hi Joseph,

    Great news, thanks for letting me know…I guess you’d better start breeding zebra finches so you’ll have plenty of tiny eggs!

    You’re probably at a 1:1 ratio of water substrate by weight, given the consistency. That has worked…drier is trial by error based, I’d say stay as is now and watch closely;

    Open egg container once daily for air exchange. If moisture level seems to work, you can weigh entire container – any weight loss shown on subsequent weighings can be attributed to water, and so you can add back the amount lost; Conveniently for mathematically impaired people such as I, 1 ml of water weighs 1 gram…

    Good luck and please keep me posted.

    Best regards, Frank Indiviglio.

  3. avatar

    Hello Frank,

    Haha, will have to convince the roomates first! I have been to bugger a few off of petstores(hard as in stores that don’t provide nestboxes the finches often don’t lay). I did come across one breeder who has raised several clutches mostly on tubefeeding the babies about 1-2 ml every 2 weeks or so, increasing as they get older. Unless I start up a good sized flight cage this seems like it might be a more viable solution.

    I was doing research on incubation media and recently came across a talk on a new product called Superhatch (by Repashy). It is composed of arcillite clay, which I happen to know quite well as it is also used in Home Depot’s Aquatic Plant Soil. A big advantage that they touted was the ability to determine moisture by looking at the substrate(whereas perlite remains white irregardless of moisture content arcillite is tan when dry and turns various shades of red brown when wetted). It holds a lot of moisture and clumps well when wet(I used a mix of it and sodium bentonite clay to build backgrounds in my 46 gallon bowfront viv. So long as the back stayed moist it worked great.) Any thoughts on this product? I don’t have a gram scale here at home, so the idea of being able to visually keep track of moisture levels is appealing.

    Thanks much for all the help!

    ~Joseph

  4. avatar

    Hi Joseph,

    I’ve always been counseled to stay away from materials that pack and do not allow for air flow, and my own experience bears that out…had poor success with topsoil as well. I think clay might even clog air pores on lower surface of the egg.

    We originally used vermiculite at the Bronx Zoo, then went to the large grain type which allowed for more air circulation and noticed an improvement. Have used sphagnum for some geckos, Tribolonotus as well.

    In a closed incubation container (in almost all cases best to use such), water loss will be minimal, opening every day or 2 will allow enough oxygen exchange. As the eggs develop, can open more frequently and leave lid cracked as hatching time nears – but in most cases closed lid is fine even if young hatch unexpectedly.

    Good luck and please keep me posted.

  5. avatar

    Hello Frank,

    Arcillite is composed of fired granules that, despite holding lots of moisture and staying together, would provide great airflow also. Similar consistency to perlite, only it is reddish and harder(almost like gravel, but then it is even more porous than perlite). Apparently another use is for certain kinds of kitty litter.

    Have you had any trouble with eggs either rupturing or collapsing? i’m assuming if they proper humidity is attained you don’t have to worry about this but it’d be nice to be able to troubleshoot and detect any bad signs.

    Never dealt with any shelled eggs before so I find this all quite fascinating. I can’t imagine the anticipation of having lots of eggs incubating.

    All the Best
    ~Joseph

  6. avatar

    Hello Joseph,

    Thanks for the note…sounds interesting, might be worth a try – in past I collected red eared slider eggs from a favored site along Bronx River, and used them to test out new materials (of course, they sometimes hatch under the worst of conditions, so perhaps not best choice!).

    You’ll usually see the eggs start to “dimple” or sink in a little at a time if they are too dry, will collapse if too much time goes by. Rupturing I’ve only seen due to bacterial action – gasses on dead eggs – they can get “plump” from too much water, but that’s hard to determine and not really all that common.

    It is exciting – if you start breeding in any numbers, a Commercial Incubator is the way to go.

    Good luck and please keep me posted.

    Best regards, Frank Indiviglio.

  7. avatar

    Hello Frank,

    Let me know if you do. I may try that if I get any eggs in the future.

    One of the eggs was laid close to the entrance of the laybox so had a bit of a dent/lump in it from th beginning. This has lessened somewhat but the egg is also turning a bit of a tannish/yellowish hue. Is that a bad sign? That being said I’ve seen photos of some pretty nasty looking eggs hatching, however.

    Thanks!
    ~Joseph

  8. avatar

    Hello Joseph

    Yes, snake eggs that seem “hopeless” can hatch. I’d leave it – discoloration is not so much of a bad sign as with amphibian eggs, and fungus tends not to spread as rapidly as it does in aquatic eggs. Just watch that nothing appears to be growing on the shell.

    Good luck and please keep me posted.

    Best regards, Frank Indiviglio.

  9. avatar

    Hello Frank,

    Update on these eggs.

    Of the 5 eggs, 3 appear to be perfect with no signs of any discoloration(at least in areas visible to me). One had a small amt of yellow on it,hard to tell if it is mold or not, seems like it might be so I brush the area ever few days. The bottom egg(they are all stuck together sort of like a missile pod) has turned quite yellow at one end and dented in quite a bit. I moved the perlite around in hopes to rehydrate this egg(I’m guessing the perlite around it dried and sucked all the water out of it).

  10. avatar

    Hello Joseph,

    Thanks for the update. Sounds like you are doing well – lower egg might be infertile, but best to continue as you have been doing,

    Good luck and please keep me posted.

    Best regards, Frank Indiviglio.

  11. avatar

    Hello Frank,

    Appears you are correct on the bottom egg as it is now turned yellow, moldy, and also dark in a part. I suppose it will start to disentegrate. Should I worry about it?

    Also, any suggestions for the female? Based on the clutch size(someone else reported his nearly 10 yr old CB animal laid a clutch of ten and does this several times per year) she was likely a bit young for this(hard to tell with a WC animal) and I’d like to keep her from laying any more this year if possible. She has eaten several button quail eggs since then and also coturnix eggs(but for whatever reason is having more difficulty crushing them now…I found one egg with cracks down to the membrane but still intact, another egg she only partially drained). I’m thinking feeding her sparingly would be the best thing to do.

    All the Best
    ~Joseph

  12. avatar

    Hello Joseph,

    You can remove it if it’s possible to do so w/o damaging adjoining egg.

    Prolific snakes usually keep on laying no matter what, unless subjected to severe stress; unlike birds, removing nest sites usually does not work. I’ve never run across anyone who has done it by scaling back on food – no real guidelines.

    Recently, it’s been discovered that some snakes are able to keep growing despite long fasts! Better to feed heavily and allow her to re-build; I wouldn’t worry about draining effect as long as you keep up her food intake and she does not have difficulty passing eggs.

    Good luck and please keep me posted.

    Best regards, Frank Indiviglio.

  13. avatar

    Hello Frank,

    Moisture level has been dropping and some of the eggs have caved in quite a lot. I went ahead to add what water I thought was lost and put some newly moistened perlite over the eggs. I’ve heard of misting them but do not have a mister here currently. any idea how long it should be till the eggs fill in again?

    Thanks!
    ~Joseph

  14. avatar

    Hello Joseph,

    No real way to judge, best to re-hydrate gradually as you have been doing. Once eggs appear full, get hold of a gram scale and weigh the container…any weight lost after that will be water, which can then be added back (1 ml water weighs 1 gram).

    Good luck and please keep me posted.

    Best regards, Frank Indiviglio.

  15. avatar

    Hello Frank,

    Must have done something wrong as I am down to 2 normal looking eggs. The bottom one shriveled up and I opened it to reveal dried yolk inside. The bottom two 2 within the last few days appear to gotten the same bacterial infection as they are shriveling up and somewhat wet on the bottom(even though the media seemed bout right). The two on the top still look ok. Looks like I have much to learn…hopefully will have more eggs to hone my skills on soon.

    all the Best
    ~Joseph

  16. avatar

    Hello Frank,

    Just thought to update that we are still at two eggs(the two on the top of the pod, including the one that looked iffy to me in the beginning). It seems the ones in contact with the perlite had trouble. I think it also had to do with me constantly peeking in on them. Anyway I’ve been opening to check maybe once two weeks and also brushing the eggs off in case of mold. Despite sitting on top of moldy eggs they look plump and have grown a bit.

    Here’s hoping something comes out of this!
    ~Joseph

  17. avatar

    Hello Joseph,

    Thanks, I meant to ask about the eggs in my earlier comment….please let me know if (when!!!) they hatch,

    Good luck, enjoy and please keep me posted.

    Best regards, Frank Indiviglio.

  18. avatar

    I am pleased to report that I came back(from Joshua Tree NP this weekend) to a cute little hatchling eggeater. Hope one more follows!

    ~Joseph

  19. avatar

    Hello Joseph,

    Thanks for letting me know, congrats! I look forward to updates, hope you can line up finch eggs.

    Good luck and please keep me posted.

    Best regards, Frank Indiviglio.

  20. avatar

    Hello again Frank. I caught him or her. Just shy of a foot long. Black and grey splotches. View them on face book…search for

    mark s henry in Marshall. Will look for friend request…if you do the Facebook thing that is. This is great…cya

  21. avatar

    Hi. I bought some new vermiculite yesterday and a a larger container. I moved the eggs to the larger container making sure not to turn the eggs over. I have noticed that their are white chalk marks on the front and middle of the eggs so I figured that is the front pof the eggs. Many people from other forums have also stated that this makes them likely to be fertile. The only problem is that the vermiculite that I bought yesterday is organic vermiculite and seems to not to be as moist as the vermiculite that I had been previously using. This has lead me to periodically spray the vermiculite and eggs. I feel that this is helpful because I am misting the substrate and eggs and not dampening it. I also do this because the water quickly evaporates and the substrates seems to quickly become dry again. I am not really good at math and do not understand the water to vermiculite ratio that you have mentioned. Is it similar to adding a teasooon or spoon of water to the
    Vermiculite. I don’t have an incubator and currently using a tank filled water and placed a container filled with vermiculite and the eggs on top of two bricks. I am using a subsmersible water heater to raise the water temperature. The water temp is about 88 degrees. I drilled holes in the top of the container that the eggs are in for venalation. I covered the tank with a towel to hold the heat and humidity in. Do you think that this method is okay and will help the eggs to hatch. I would love some more advice and suggestions. Thanks

    I don’t,t have an incuba

  22. avatar

    Hi Shaun,

    The tank incubator should be fine; I’ve used them often in the past.

    The vermiculite shouldn’t dry out…rather, perhaps start a new batch; add water gradually until the substrate sticks together as described. You can take a bit into your hand several times weekly to squeeze and check moisture level. Add some water slowly into the substrate if needed. Best not to spray the eggs, as water directly on the air pores in not a natural situation…the eggs should absorb water gradually, through the substrate. Hope all goes well, frank

  23. avatar

    I have 3 box turtle eggs that I thought should of already hatched. Today makes day 84 and 2 of the eggs have dents in them and the other looks fine. I did try and candle them couple days ago and can’t seem to see anything, not sure if I’m doing something wrong or not. But I can almost be positive when just looking at the eggs I can see movement inside, almost like the babies are streching or something. And at times it looks to me like the eggs are slightly shaking….is this possible or are my eyes playing tricks on me. I was told there is noway to see baby moving inside the egg shell.

  24. avatar

    Hi Becky,

    They generally hatch in 70-80 days, but this can vary quite a bit, and longer incubation times are common. Movement can sometimes be seen just prior to hatching. best to leave them…nothing to be done if they are not viable anyway, so I would handling/disturbing. Hatchlings sometimes (rarely) need help exiting the egg, but you will notice cracks or other evidence. I hope all goes well, please keep me posted, frank

  25. avatar

    Thank you Frank, I am gonna remain hopeful and pray for the best. Maybe they just need a little more time. I will let you know the outcome.

  26. avatar

    Hope to hear some good news, Becky; best, Frank

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About Frank Indiviglio

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Being born with a deep interest in animals might seem unfortunate for a native Bronxite , but my family encouraged my interest and the menagerie that sprung from it. Jobs with pet stores and importers had me caring for a fantastic assortment of reptiles and amphibians. After a detour as a lawyer, I was hired as a Bronx Zoo animal keeper and was soon caring for gharials, goliath frogs, king cobras and everything in-between. Research has taken me in pursuit of anacondas, Orinoco crocodiles and other animals in locales ranging from Venezuela’s llanos to Tortuguero’s beaches. Now, after 20+ years with the Bronx Zoo, I am a consultant for several zoos and museums. I have spent time in Japan, and often exchange ideas with zoologists there. I have written books on salamanders, geckos and other “herps”, discussed reptile-keeping on television and presented papers at conferences. A Master’s Degree in biology has led to teaching opportunities. My work puts me in contact with thousands of hobbyists keeping an array of pets. Without fail, I have learned much from them and hope, dear readers, that you will be generous in sharing your thoughts on this blog and web site. For a complete biography of my experience click here.
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