need to heat themselves by the sun, so various bulbs may be necessary to simulate this in a terrarium. Also, certain plants or diurnal animals need a source of UV to help synthesize Vitamin D and assimilate calcium. Such UV can be provided by specialized fluorescent tubes or daylight bulbs, which recreate the reptiles' natural environment and emit a more natural sunlight effect compared to the blue glow of a fluorescent tube. A day/night regulator might be needed to simulate with accuracy the alternation of light and dark periods. The duration of the simulated day and night depends on the conditions in the natural habitat of the species and the season desired. Temperature The temperature can be a very important parameter for species that cannot adapt to other conditions than those found in their natural habitat. Heating can be provided by several means, all of which are usually controlled by a thermostat: heating lamps or infrared lamps, hot plates and heat mats, providing heat at the base or sides of a terrarium, heating cords or heat mats placed beneath the substrate, heat rocks, or more complex equipment generating or producing hot air to the inside of the vivarium. Similar to lighting, a decrease in temperature might be needed for the simulated night periods, thus keeping living species healthy. Such variation need to be coherent to those found in the natural habitats of the species. Thermo-control systems are often used to regulate light cycles and heating, as well as humidity (coupled to built-in misting or rain systems). Light-dependent resistors or photo-diodes connected to the lighting are frequently used to simulate daytime, evening and nighttime light cycles, as well as timers to switch lighting and heating on and off when necessary. Humidity Many plants and animals have quite limited tolerance to the variation of moisture. The regulation of humidity can be done by several means: regular water pulverization, water evaporation inside (from a basin, or circulation of water), or automated pulverization systems and humidifiers. Ventilation and openings Access inside the vivarium is required for the purpose of maintenance, to take care of the plants and animals, or for the addition and withdrawal of food. In the case of some animals, a frontal opening is preferable because accessing a vivarium from the top is associated by some species with the presence of predators and can therefore cause unnecessary stress. Ventilation is not just