Sometimes I am asked questions about the care of the tropical lizards called basilisks. There are in fact a number of basilisk species, although not all of them are common in the exotic pet trade. One typical species might be the common basilisk of Central America, Basiliscus basiliscus. This species grows up to 75 cm or 30 inches long, of which the tail is responsible for up to 3/4 of its total length. The males of B. basiliscus are the larger sex per length and mass, and they possess more prominent dorsal and cranial crests. The snout to vent (or head and body) length of the adult male basilisk is between 1/5 and a 1/4 longer than that of the aduly female. However the degree of sexual dimorphism observable is greater in the species B. plumifrons and B. vittatus, than in B. basiliscus. Basilisks stereotypically inhabit tropical forest beside ponds, streams, rivers, sinkholes and sometimes even the sea; however, at least two basilisk species, B. plumifrons and B. vittatus, may also be found in forest far from the water, so some species of basilisk are more generalist than are others. B. basiliscus is found in suitable habitats of Central America, from Mexico to Panama, and into the north of Colombia and Venezuela. All of the basilisks are in fact found in Central America and the northernmost part of South America; surprisingly, they are not present as far south as Amazonia.
The same is true of the extant lizards that are the closest relatives of the basolisks, and with which they form a clade of climbing lizards, called the corytophanids (the helmeted or casqued lizards). Curiously, several fossil corytophanids are known today from localities in Europe and North America, where they thrivved during a time when the climates of these continents were warmer. The present distribution of corytophanids is suggestive that they colonised South America late and during a faunal interchange of animals between North and South America. Although they went extinct in the northern faunal realms, their range into tropical South America appears rather marginal. Basilisks stand out among other lizards, because they are visually regognizable by their contours. The notable bony head crests of corytophanids are formed by the bones pf their cranial vaults, and they first evolved as attachment points for the inserion of muscles that are associated with biting. In basilisks, the male of the species grows a lighter expansion of the crest, that happens to play no role in increasing their bite force. Similarly striking to the observer, are the tall, dorsal structures that are supported by long, slender neural spines rising from atop their backbones, thus forming elegant and remarkable sails crowninp their torsos and tails. Similar sails are seen in some other lizards today, and also in some extinct animals.
The basilisks are renowned for their amazing ability to run bipedally at the water surface, a habit that has earned them (and especially B. basiliscus) the name of Jesus Christ lizard. Although this ability is not exactly unique to the basilisks in the animal kingdom, it is an exceptional talent that is reminiscent of a miracle. When it is running along the water surface, the basilisk is dealing with the surface tension of a yielding, liquid surface; this is something difficult because it is unstable, and without a special running technique, the lizard would naturally sink towards its feet. The feet of a basilisk are large and their long toes are flanged at their sides with rectangular flaps of skin. These outgrowths trap air bubbles when the basilisk slaps down its foot fast, generating briefly an air filled pocket that displaces the surface water long enough to bear its weight, as the lizard pushes its foot back against the air pocket for forwards thrust; the foot must be retracted from the water fast, before the air cavity collapses. The flaps of skin maximise the surface area that is available upon contact between the feet and the water surface, and it is important that the water surface be disrupted as minimally as possible.
In the water, juvenile basilisks swim by side to side oscillations, assisted by frog kicks. Though the dorsal crests or sails of basilisks may look like the fins of a fish, they are anatomically quite different and actually make these lizards less efficient in the water, because they make their bodies more rigid than are those of most other lizards. Thus basilisks perform a frog kick to compensate and to make good use of their intermembral disparity once they are in the water. Basilisks are slow runners, but they are agile, and their dependence upon their hindlimbs is good for extra thrust during climbing or when traversing uneven ground. Basilisks prefer to run on the water towards the safety of an item such as a floating water hyacinth, than to dive neneath the surface, although they are recorded to dive at least as deep as 3 and a 1/2 meters down. Typically basilisks are thought of as arboreal lizards that enter the water only to escape predators, but their gut contents demonstrate that some aquatic hunting occurs as an individual habit. Basilisks can be reluctant to take to the water for wariness of dangers from aquatic predators. Big, carnivorous fishes are known to attack them as they traverse the water surface. Amphibious foraging by the basilisks appears concentrated in the safety of shallow streams.
Basilisks can be skittish and injure themselves by darting off, at which point they hit themselves on the sides and especially the glass. Not all of them are, and in fact captive bred and long term captive animals may be quite tame; in which case they are regarded as a good pet lizard. Because spooked basilisks may be prone to dart off recklessly, skittish aquisitions should be housed in a large vivarium, and a room sized vivarium might well be optimal for this reason; it is also the best for accommodating a breeding colony. The minimal acceptable terrarium footprint for a calm basilisk, is said to be 2 and a 1/2 times its total length in both directions. But it matters that the juveniles will use the floor space more than will the adults, which is because they grow increasingly arboreal with age. Adult basilisks, especially, need height to climb more than they require floor space. Male adult basilisks will fight between themselves, but the females will share if the environment is sufficient for them spatially. Each lizard will need at least a fifth more floor space additiona to that for just one lizard. Whereas zoos regularly cohabit basilisks with other lizards, and with turtles, fish, stingrays, birds, and mammals. They will however eat what fits into their mouths, rarely including such prey as rodents and snakes, so care may ne taken as to the size of the other animals within their exhibit. Basilisks may be cannibalistic, so this same caveat must apply to keeping them with one another. Wild basilisks willingly share foraging sites and beaches with other species, and they will even climb onto large mammals to consume insects there.
The dietary habits of basilisks are well known but what they are willing to eat can be personal: some captive basilisks refuse to eat items that will not move, and some of them refuse to eat plant materials such as fruit. Purposeful plant consumption is limited to large individuals, and predation on fish, frogs, squamates, and mammals is only opportunistic: their primary food source throughout life is arthropods, both terrestrial and aquatic, but they do not dig for prey. As a result basilisks consume more winged insects than they do larvae. Adult basilisks possess a stronger bite force than do the juveniles, which are less likely than the adults to consume slow or stationery items, although they have been observed to scavenge after crabs that were feeding on barnacles, but they do not consume cracked eggs although they attract insects that the juvenile basilisk eats. The juvenile basilisks forage more on the ground than do the adults, and out in the open among grasses, or on the beach. Thus the juvenile basilisks are ecologically different in their habits than the adults. In principle basilisks should consume nonmoving items, though even when they are mature and more omnivorous, their diet should remain dominated by lean animal protein.
By their nature, the basilisks are heliothermic baskers and behavioral thermoregulators, so a heat lamp and UV source is ideal; however in reality heliotherms are really getting warm by conduction from substrates heated by the sun. Basilisks take care to avoid the sun when substrates are the hottest: they bask at tempertures of 26 to 33 degrees centigrade, function best at 35 degrees centigrade, and avoid tempertures of 38 degrees or above. The humidity ought to befit a rainforest biome, perhaps 75 to 90 percent, although it can fall lower without ill effect; and if in doubt the reptile owner should have more concertn that the terrarium is ventilated well. (This is because stagnant air is far more dangerous to reptiles, than is lowered air humidity.) They need an opportunity to climb, and in the wild they can be found in trees as high as twenty meters above the ground level, and they also climb onto river rocks. Even the toe fronges that the basilisk uses to run on the water, first evolved in the trees because they are shared by other corytophanids too. The relative stiffness of the basilisk torso surely aids it when climbing, and the tendency towards reduced lateral mobility is also seen in unrelated climbing animals.
