The Cold Blooded News

The Newsletter of the Colorado Herpetological Society

Volume 28, Number 7; July, 2001

Iguanas in Heat

Reprinted from Ark'Type, the Newsmagazine of the WSPCR (the Westcoast Society for the Protection and Conservation of Reptiles), February/March 2001

Domestic iguanas go into their breeding season at any point of the year, but spring always seems to be the time when a majority of iguanas enter their cycle. Some iguanas will not go through a noticeable breeding season, while others will be very noticeable! Often poor health or an enclosure that is too small will prevent the cycle. This is for the best (though even unhealthy iguanas may try to lay eggs and this can be fatal) since a female needs to be in optimum health to survive egg production, which she will do with or without a male to copulate with (the eggs of course would not be fertile if there was no copulation). Often an increase in the health or environment of an iguana will spontaneously stimulate the onset of breeding season. This is common in a rescued iguana or an iguana who suddenly gets exposed to proper UV (or even just boosted UV such as when the old UV light is replaced).

Age-wise an iguana typically reaches sexual maturity by 2 years. Size, however, rather than age is the true measure of sexual maturity. A snout to vent length of six inches in a male and 10 inches in a female makes them big enough to start cycling.

In general the male will go through an "aggressive" time. This is not always so and is to different degrees in different iguanas. It can also be influenced by the owner. If an owner allows a male iguana to have run of the house and sit on perches above their eye level there is a good chance the iguana will perceive himself to be in the alpha position and thus feel it necessary to assert his dominance in breeding season. In the wild male iguanas are in season for about 30 days but in domestic iguanas there seem to be no rules -- some males barely seem to have time to breed while others seem to be in season forever!

Behaviours to typically expect from a male in this time are: aggression, dominance, biting, tail whipping, need to roam territory, development or deepening of orange colours, everting of the hemipenes, and ejaculation. An iguana owner has to learn how to be firm and not be dominated but at the same time know when to leave iggy alone with his hormones! Remember the two things you could be to a male in breeding season are a mate or a competitor. Try to be patient and understanding and just give him his space but always make sure you are the boss.

Females are a worry during their cycle. They will produce and usually lay eggs no matter if there is a male present. Sometimes the eggs are reabsorbed and the cycle is not even noticed by the owner. Female iguanas are receptive to copulation for about one week; after this the eggs begin to develop. The entire gestation period lasts 8 weeks. It is in the last four weeks that things get noticeable. The iguana will slowly decrease her appetite and cease eating altogether. She typically goes the last four weeks with no food. Her fat deposits (on the tail mostly) slowly disappear while her belly gets big and near the very end develops a visible lumpiness. She will spend all her time basking and searching out potential nest sites and near the end will begin digging everywhere. It is important to introduce a nest box early on in the whole process so that she has time to accept it. It needs to be big enough for her to be comfortable in and can have a variety of mixtures as a digging medium, the simplest being peat moss, with enough water so that tunnels dug keep their form.

Egg binding is a very dangerous possibility during a female's cycle. This occurs when an iguana will not or cannot lay her eggs. It happens in iguanas which are not in tip top health, when a suitable (in the iguanas eyes) nest site is not available or for many other reasons including egg deformity due to infertile eggs. This is a tricky time and if egg-binding occurs it can kill very quickly. Typically emergency surgery is required to remove the eggs and spay the iguana. Signs of egg-binding are depression and lethargy following a period of incessant digging.

A female iguana producing eggs should be given extra calcium and have vet check ups. If you keep her healthy, visit the vet, give her a suitable nest box and cross your fingers hopefully everything will go smoothly. As for the eggs. ...it is said they are quite tasty hard boiled.