Housing a male and female leopard gecko together is necessary for breeding and it provides a window into the behavioral interactions between two members of the same species. Preventing problems during this process involves considering the appropriate age and size of the geckos as well as the size of the habitat and what to do when they breed.
When to Introduce Them
Do not introduce a male and a female leopard gecko until both are at safe breeding size. For both males and females, 1.59 ounces is a sufficient size for breeding. The female should also be at least 9 to 10 months old and in perfect health. The male should also be in good health, but may be as young as 5 months. Introducing the geckos when they are too young can lead one partner, usually the male, to rapidly outpace the other in growth by stealing food and bullying the other.
Never house two sexually mature male leopard geckos together. They are territorial animals and will fight, occasionally to the death, if kept together.
Housing two animals in a space meant for one is never a good idea. House a pair of leopard geckos in a 20-gallon aquarium. Do not use an aquarium of less than 10 gallons as a habitat. Because aquariums of the same volume come in different shapes, remember to look for a tank that will provide the most floor space and is at least 1 foot tall.
If you house a male and female together, be prepared for them to mate, regardless of other conditions. Temperature and light cycling can provide better conditions to encourage mating, but especially resilient geckos will breed in any conditions. Make sure the female is getting enough to eat. Dominant males may steal food and leave a malnourished female who will not produce viable eggs.
Dust all insects with calcium and vitamin D3 supplement powder before feeding. Immediately upon introducing male and female, provide the female with an egg-laying container consisting of well-moistened vermiculite in a 16-ounce deli container with a hole cut in the lid for her to climb in and out of. Egg-laying can occur as soon as 16 to 22 days after copulation, which you may not witness. Have an incubator and habitats for baby geckos prepared in advance -- you don't want babies running around with adults, as they will be taken for food.
Mating rituals in leopard geckos can be quite violent. The male will bite the female on the tail, back and neck before mounting her. Check closely for any injuries after copulation, but in general, males will not intentionally significantly harm females.