Reptiles: Reproduction "From Egg to Adult"

Synopsis: Some reptiles lay eggs and others deliver live young. Females do not need the presence of a male in order to lay eggs. There are subtle differences between males and females in most species of reptile, but in others, the differences are obvious. Reptiles can also be sexed by probing, visual exam, ultrasound, surgery or radiographs. Most reptile eggs are artificially incubated.

Reptiles are increasing in popularity as pets, and with this interest comes a demand for healthy, domestically bred reptiles and amphibians. Many hobbyists are becoming curious about the possibility of breeding their pets. Other reptile owners are doing such a good job of caring for their pets that the herps are growing, reaching a point that they are becoming sexually mature. For example, we are seeing an unprecedented number of adult female green iguanas presented to veterinary clinics for problems related to egg laying.

Most reptiles lay eggs. The act of laying eggs is called oviposition. Reptiles that lay eggs are called oviparous. Some reptiles bear live young, and the term for this is viviparous. Technically, a female that lays eggs is said to be gravid when she is holding eggs inside of her. A female that gives birth to live young may correctly be called pregnant.

Below is a list of some of the more common species of reptiles and the method of reproduction they employ.

Egg Layers
All turtles
All tortoises
All crocodilians
Some lizards
Water dragons
Veiled chameleons
Panther chameleons
All pythons
Rat snakes
Corn snakes
Some lizards
Solomon Island skink
Blue-tongue skink
    Shingle-backed skink
Some chameleons
Jackson's chameleon
Some snakes
All boas
All vipers
Garter snakes

Male and female reptiles do not have external genitalia to help owners determine the sex of a herp. Males and females do possess different reproductive organs, however. The male possesses two testicles, housed inside the body. The male also has a copulatory organ, either a single penis (turtles and tortoises, crocodilians) or a pair of hemipenes (lizards, snakes) that can often be seen as two bulges behind the cloaca at the base of the tail. The penis or hemipenis is not connected to the urinary tract, and is strictly an organ of reproduction. Lizards and snakes can be sexed by the use of a probe that is inserted into the cloaca, directed towards the tail, off of the midline. The probe will travel farther in the male than in the female.

There are also secondary sexual characteristics that can help differentiate males from females. Often, in male chelonians (turtles and tortoises), the plastron (bottom shell) is somewhat concave, and the tail is proportionally longer. Often, the head and general body size are proportionally larger in males of reptile species. The male Jackson's chameleon has three prominent horns on the head that are lacking in the female. Many male iguanids and geckos possess femoral or preanal pores that secrete a waxy substance making them more prominent than those found in females. Many boas and pythons possess spurs located on either side of the vent, and in many males, these spurs are larger. In general, the tail of male reptiles is proportionally longer than the female's.

There are other ways to differentiate the sexes of reptiles, including ultrasound, surgical sexing and radiographs. For specific information, please consult your herp vet if you are unsure about the sex of your reptile.

While it would seem that reproduction is a natural event, without correct circumstances, such as a balanced diet and a suitable environment for egg-laying, eggs may not develop normally or be laid in a timely manner. Owners are often surprised to find that their single pet female lizard has developed eggs. A healthy adult female does NOT need the presence of a male to become gravid.

For fertilization, a male reptile inserts either one of his two hemipenes into the female's cloaca, or the single penis is inserted. Before actual copulation, the pair usually engages in some type of ritualized courtship. After copulation, sperm can be stored for up to six years, and this stored sperm can fertilize subsequent clutches without additional contact by a male.

Using the green iguana as an example, even without a male present to fertilize eggs, a healthy adult female may begin developing eggs. The process begins with the ovaries, where eggs are stored. The ovaries are located inside the body. Most green iguana females become mature when they are between two and four years of age. At that time, follicles begin developing in the ovaries. Each follicle is composed of a tiny egg and a sac filled with yolk. The follicles then detach and move into the oviducts where the egg white is added, and then a shell is placed around the yolk and white. The gravid female usually will not eat for three to six weeks prior to laying her eggs. It makes sense since her abdomen will be full of eggs in the oviducts, and the stomach is quite compressed, and there is little space for food in the stomach.

If a female iguana is gravid and does not have a suitable site for digging in order to oviposit, she may become egg-bound. A gravid female would naturally dig a large burrow in moist soil (often along a riverbank) in the wild. Without a suitable site, she may hold her eggs for a much longer period of time than is normal or healthy. Since a gravid female usually isn't eating, she may lose body condition, and she may also suffer from problems with low blood calcium. Providing a gravid female with a large trash can filled with 50% sand and 50% potting soil, kept in a location at about 85-90 degrees F, may be enough to allow her to dig and lay her eggs.

However, if she does not lay her eggs and she begins to lose too much weight, she may require emergency veterinary care. Medications can be tried, and if that fails, she may require surgery to remove the eggs. A herp veterinarian may suggest performing a "spay" (removal of the ovaries and oviducts) to prevent future problems, at the same time that the eggs are removed.

Female pythons are one of only a few groups of reptiles to care for her eggs after oviposition. A female will coil around her eggs until they hatch, protecting the eggs and providing temperature regulation, as well. Some turtles, lizards, king cobras, cobras and all crocodilians guard their nests. Crocodilians also assist the hatchlings as they emerge from their nests, and will guard them for a while after hatching.

In the species that give birth to live young, some species show a degree of maternal care. Some skinks will assist the neonates by helping them escape from their birth sacs. The Solomon Island skink gives birth to one very large offspring after a long gestation period and while pregnant, she will eat very little. Snakes, such as the boas and garter snakes, give birth to live young.

In the species that lay eggs, in most cases, the gravid female digs a hole, deposits the eggs and then completely covers the hole, hiding any evidence of her activities.

In captivity, eggs are usually removed and placed in an incubator. Vermiculite is moistened with bottled water and the eggs are buried halfway. Eggs should be handled carefully, and care should be taken to not change the position that they were in when deposited. There is some controversy as to whether or not rotating reptile eggs can be detrimental, so if at all possible, mark the top of each egg with a dull pencil, and place the egg in the vermiculite in the same position.

The eggs of some species are hard (turtles, tortoises, crocodilians and some lizards, especially geckos), and those of others are more leathery (snakes and most lizards). Incubation parameters vary from species to species, and in some species, the incubation temperature will influence the sex of the offspring. Incubation time can vary from about 45 days (in small lizards) to over a year (for some tortoises).

When it is time for the baby to hatch, the neonate uses its egg tooth (also called caruncle) to cut through the eggshell. The baby will usually remain in the egg for 12-48 hours after it pokes its head through the egg. During that time, any remaining yolk still attached to the hatchling will be absorbed.

Neonates hatched from eggs, as well as those that are born alive from the female, are able to fend for themselves as soon as they are up and walking around (or slithering).

Some species of reptile are very easy to breed in captivity. This can be a fun and educational experience for herp owners, and it can be rewarding financially, as well. With the small investment of an incubator, healthy breeding stock, good nutrition and proper environment and appropriate veterinary care, it is possible for even the novice herper to successfully breed and raise reptiles.

Copyright 2006 Margaret A. Wissman, D.V.M., D.A.B.V.P.
All Rights Reserved

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