Egg-laying in lizards
Lizards (saurians) are mostly oviparous, meaning the females lay eggs. The clutches are usually staggering in number and fill the female’s coelomic cavity entirely; she is generally off her food as the pregnancy progresses. In the green iguana (Iguana iguana), the average clutch is 40 to 50 eggs. The gestation period varies with the surroundings; in the Chinese water dragon (Physignathus cocincinus) it averages 2 months.
The biggest medical problems linked to breeding are those caused by an unsuitable laying site. In the wild, lizards choose their laying spot with great care and find a depth and a ground to their liking, which is why “egg-laying trouble” is rare in wild lizards.
In captivity, on the other hand, the laying site is often underestimated. Nowhere to lay, no suitable substrate, not enough depth to bury the eggs, too much stress, other cage-mates, and so on — the mistakes are many. If the female is not satisfied, she will refuse to lay, which leads to egg retention (egg binding, or dystocia) that grows complicated and often calls for medical care, or even surgery.
One option is to provide a laying box in the terrarium. This is like an opaque container with a small entrance on the side (the same goes for snakes, with the opening on top). Fill it halfway with slightly damp — but not soaking — substrate (vermiculite, sand, sometimes sphagnum moss, for example). At least 80% humidity is needed. The ambient temperature should be set to around 28-30°C. The substrate must be deep enough: for the iguana, allow 30 to 60 cm of depth!
One snag is that the female sometimes prefers to shun this strange box and tries to lay beside it. An alternative is to turn the whole terrarium into a “laying box”. In that case, add a dry platform on top for resting, fitted with a heat lamp.
Once the eggs are laid, there are two possibilities: either the eggs are dried out and should be discarded, or they look fresh and stand a chance of developing. You can then try to incubate them.
Incubation:
28-30°C
90-100% humidity
Bury the eggs halfway in damp vermiculite and cover them with about 3 cm of slightly damp sphagnum moss.
For Physignathus cocincinus eggs, allow roughly 2 months of development.
If the eggs were not laid in a suitable place (up high, for instance, as with some geckos), they can be moved to an incubator. Take care not to turn them over!
If some eggs change colour and the shell starts to dry out, be sure to remove them or empty their contents with a syringe and needle, to reduce the risk of bacteria spreading to the healthy eggs.
Diagrams and further information can be found in the Atlas de terrariophilie, vol. 3, Les lézards, published by Animalia.