Snakes are either oviparous (egg laying) or viviparous (live bearing). Those species that produce live young are usually found in cooler climates or at higher altitudes. Unlike tortoises, turtles, alligators and crocodiles, whose gender is determined in large part by the incubation temperature, the gender of a snake is determined by its genes, as it is in the case of birds and mammals. Snakes that lay eggs do not typically build or dig nests, in the manner of many other reptiles. The King Cobra is an exception.
Snakes in their natural environments select a nest site, which has an appropriate temperature and humidity range, as well as the correct substrate. If specific environmental needs are not met, the eggs will not hatch. Some species select a crevice in which to lay. Grass snakes choose to lay their eggs in decaying vegetation, which produces heat as it decomposes.
Of the species commonly kept as pets, only a few species of pythons actively brood their eggs. Female Burmese pythons coil about the eggs and use rhythmic contractions of their muscles to produce heat to warm the eggs. They loosen the coils to decrease the temperature at which the eggs are kept when ambient temperature rises or toward the end of incubation. Some pythons will leave the clutch for a short time, bask and then return to transmit the absorbed heat to the clutch.
Unlike some pythons, most snakes do not care for their eggs after they are laid. Once the eggs have hatched, maternal care is negligible or non-existent. There are a few exceptions, however. Some viper species will stay with their young until after they shed for the first time.
In spite of the intricacies and unknowns of the natural process, attention to detail and sound research will allow healthy snakes to be hatched in captivity. Familiarize yourself with the natural habitat, breeding and nesting behaviors and needs of your species.
The egg producing species kept commonly in captivity are members of the Pythonidae and the Colubridae groupds. All pythons lay eggs, ranging from 15 and 30 in a clutch.
Most of the colubrid species lay 15 to 20 eggs in a clutch. This includes kingsnakes, milksnakes, rat snakes and corn snakes. Rough green snakes lay just four eggs. Western hog nosed snakes and the grass snake lay up to 30 eggs.
Boas and garter snakes (a Colubrid type snake) are live-bearer snakes that are commonly kept and bred in captivity.
The incubator must insulate the eggs against heat and humidity losses and significant ambient temperature fluctuations. They may be homemade, such as a plastic container, which holds the eggs. This container is then placed inside an insulated box, such as a styrofoam cooler. Or, the incubator can be purchased commercially.
An incubator should be running for at least 48 hours before it holds eggs to allow you to be sure that temperature and humidity variations are within acceptable limits. The principles of a good reptile egg incubator apply equally between homemade and commercial incubators and include:
Given that the safety margin narrows when the eggs spend more time at the upper end of the range, a more moderate temperature and slightly slower growth rate are preferable. Temperatures above and below the range will increase the incidence of abnormalities and fetal deaths.
Temperature should be controlled by a thermostat, and at least two thermometers (not just the one sold with the incubator) should be clearly visible. Digital thermometers with remote sensing probes work well. A maximum-minimum thermometer is highly recommended.
The temperature must be checked at the level of the eggs and heat should be spread uniformly throughout the incubator. The eggs must not sit on "hot spots" or next to a ventilation port. Commercial incubators are usually equipped with heating coils and thermostats. In the case of a homemade incubator, the heat source can be a heating coil or a submersible aquarium heater. It is not recommended that the incubator simply be placed on a heating pad, as this is a potential fire hazard and does not allow particularly fine temperature control.
The moisture level must be checked regularly during incubation and water added as necessary. Some authors suggest misting the eggs with tepid water or covering the eggs with sphagnum moss to increase humidity or to slow evaporation. Either technique may help if humidity is too low, but moistening the substrate interferes less with the egg itself, and so is preferable. Use a hygrometer to measure humidity. Ninety percent humidity is recommended for many species, but be sure to check the specific recommendations for your particular reptile because humidity and temperature specifics are determined by the species being incubated.
Snake egg incubation times vary and are influenced by several factors. A few weeks after the hibernation or cooling period necessary for the successful reproduction of many oviparous species, a shed will occur, which in females is known as the "pre-ovulatory" shed. At this time the male is often paired with the female, and she should ovulate in the weeks after this shed.
Copulation or mating occurs before ovulation, and in most species occurs several times over several weeks. Fertilization is the union of egg and sperm, not the act of mating. This means that the precise date of fertilization is not certain. In addition, snakes are able to store sperm, so fertilization may occur sometime after mating, and in the absence of a male. Just as the time from mating to ovulation varies, so does the time from ovulation until oviposition, or laying.
Pregnancy can be difficult to determine. The snake usually swells in the mid- to hind-section of her body, but in the case of overweight animals, the swelling can be obscured by fat deposits. The snake may bask more and her appetite may decrease. Her body position may change; she may lie on her side or may coil more loosely than normal. Close to the time she will lay, she may be more restless.
Gravid (pregnant) snakes typically shed about two weeks before they lay. This is an important date to note. The swellings of eggs may be visible in lean animals and may be palpated, that is felt, by an experienced keeper or a reptile veterinarian. They may also be visible on a radiograph (X-ray). Ultrasound is the best and safest method of determining if a snake is gravid as well as the number of eggs.
Take care when handling heavily gravid snakes. The follicles prior to ovulation, as well as the eggs in the oviduct, are fragile structures, and have been known to rupture. Once a snake starts, she should finish laying all of the eggs within her oviduct within 24 hours. If this does not occur, call a reptile veterinarian.
The developing snake embryo (early developmental stage) receives nutrition from the large yolk, to which it is attached by an umbilical cord. As the fetus (later developmental stage) develops, the yolk shrinks and sinks, so that the young snake will hatch on top of the egg. The shell contains calcium deposits, but in a lower concentration than in bird or tortoise eggs, hence the more pliable, leathery feel of the snake egg. The shell, under the appropriate conditions of temperature, humidity and gas (that is oxygen and carbon dioxide) concentrations, permits the exchange of moisture and gas, while protecting the embryo.
The three membranes inside the egg, which sustain the growing animal are:
Generally, development is faster when temperatures are at the higher end of the range. Incubation at high temperatures is not necessarily desirable, however, as the safety margin will be narrowed, increasing the chances of abnormalities and making lethal temperatures more likely. Most snake eggs should hatch in 45 to 70 days. However incubation times in some species can require months.
Typically colubrid snakes lay 8 to 14 days after the pre-lay shed, and pythons lay 18 to 26 days after the shed. Offer a nesting site at the time of the pre-lay shed, to allow the snake to become accustomed to something new in her environment. The health of the female and the environmental and husbandry conditions play a determinative role. Unlike the female bird, if conditions do not suit her, the female reptile will not lay her eggs.
It is not unusual to see egg binding or other complications in otherwise healthy animals, which simply have not been provided an adequate site to lay. For most snakes, an opaque container with an entrance hole on the top, half filled with one of the moistened substrates discussed above, will suffice. The ovipositorium (nest) should be placed within the temperature gradient of the cage, such that a thermometer at the level of the eggs reads 82 to 86 degrees Fahrenheit. To discourage the snake from laying in her water dish, replace a large dish with one in which she cannot fit to coil.
Once she begins to lay, all eggs should be produced within 24 hours. If the eggs stick together, do not try to separate them. Remove the eggs to the incubator, taking care not to rotate them. Reptile eggs lack the rope-like structures called chalazae, which anchor the yolk of a bird egg and turning the egg may cause the embryo to be crushed by the yolk.
The membranes within the egg and surrounding the embryo and the blood vessels may also be more susceptible to the shearing forces that result from egg turning once incubation has begun. Most breeders will make a light pencil mark on top of the egg to assist in its orientation. This is also a way to identify each egg, for purposes of record keeping.
Bury the egg halfway into the moistened substrate. If you are incubating multiple clutches, identify the plastic container holding the eggs. Place a thermometer at the level of the eggs. If more than one species is to be incubated, they should be in individual incubators if possible to minimize the risk of disease transmission and allow for refinement of incubator parameters.
The eggs may take on a mottled or "chalky" appearance, but there should be no darkening or collapse of the shell or fuzzy mold growth. Viable eggs are firm, slightly pliable, dry and white. The presence of mold usually indicates fetal death, while a collapsing shell indicates dehydration. If you observe dehydration, assess the moisture content of the substrate, and add more water if necessary. Consider also whether or not the ventilation might be excessive, which often leads to dehydration.
After 2 to 3 weeks (earlier with experience) candling can be used to assess whether or not the egg is fertile and alive. Candling involves holding the egg, with its orientation unchanged, over a bright light source in a darkened room. It is helpful to focus light on the egg by holding the light source under a sheet of cardboard, for example, with a hole cut in it, which is slightly smaller than the egg. You may be able to see a dark area, representing the fetus, and an organized web of blood vessels.
Experience is required to become proficient at candling. Eggs develop, or in the case of infertile eggs, decompose, in different ways, so it will not necessarily be obvious which are viable and which are not. In addition, reptile egg development rates are notoriously unpredictable, and handling the egg may well jeopardize its health. Unless performed by an experienced breeder or veterinarian, candling should not be undertaken more than once every three to four weeks.
Candling is a fascinating learning process, but the risks must be weighed against the potential for harm. And unless you are certain that the egg is non-viable (hard, dry and the yolk rattles) it should go back into the incubator, just in case. If you are sure of egg death or non-viability, remove the egg in question, as it may become a source of bacterial contamination, infecting other eggs.
Sometimes snake eggs will stick together after they have been laid. Do not separate such eggs, but monitor them especially closely at hatching, as the young snake may break through (pip) into the attached egg. If a viable egg is attached to a non-viable egg, do not separate them. Check the eggs daily, several times daily when close to hatching. Most of the eggs in a given clutch will hatch within 24 to 48 hours of one another. The snake pips with his egg tooth (caruncle), which is located at the level of his nostrils and will be lost after hatching. Usually the snake will pip at the top of the egg, and he may stay in the egg for 48 to 72 hours after pipping, in order to absorb the remainder of his yolk sac.
There are no clear rules as to when to assist, but a snake that has not pipped within 48 hours of his clutch mates should likely have his shell slit for him. This carries some risk and must be done with care. A snake that is too weak to pip will die without assistance, but slitting the shell may damage the hatchling or the membranes and yolk which sustain him. One cannot be certain that the snake is simply not yet ready to emerge; as a guide, the last egg should pip within 48 hours of the first. Seek the help of an experienced breeder or veterinarian if necessary. Leave the snakes in the incubator until they have vacated their shells entirely. Newly hatched kingsnakes should housed separately as soon as possible, as they often show cannibalistic behavior.
The serious reptile breeder keeps extensive records, but even the casual hobbyist will learn a great deal and have more success and a greater understanding of his reptiles if he keeps records. The short term value of records is not always clear, but in time will lead to a greater number of healthier pet snakes.
Mark the eggs and the container, such that you are able to identify which pair produced which eggs. In addition, note the following points specific to the breeding of oviparous snakes:
Records can often point to trends or unusual occurrences that may explain the death of the egg or of the hatchling.
Although less is known about the reptilian egg, as compared to the avian egg, a reptile veterinarian may be able to rule in or out several possibilities by performing an egg post mortem. This must be done quickly, as the egg will undergo rapid autolysis, that is, it will decompose quickly once the embryo has died.
Your veterinarian can also do a histology exam, which examines tissues microscopically. Tissue from the egg can be cultured to identify possible bacterial disease. Your reptile veterinarian can also provide an objective eye, which may be able to see a pattern in your records to explain losses.
Start with healthy, well-kept parents. Be as sure as possible that they are of similar geographic origin. Learn the species' natural history and nesting conditions by talking to experienced breeders and keepers. Record all data related to parental activity, eggs and incubation parameters. Realize that assisted pipping may save the animal, but may also kill it. There are no hard and fast rules. Make use of your reptile veterinarian and of successful breeders of your reptile's species.