Reptiles
Jackson's Chameleon
Trioceros jacksonii · also called Jackson's chameleon, three-horned chameleon, Kikuyu three-horned chameleon
The male Jackson’s chameleon looks like a Triceratops shrunk to the size of a hand — three forward-pointing horns on a bright green, slow-motion lizard that swivels its eyes independently and shoots out a tongue longer than its body. It comes from the cool highlands of East Africa, and a botched pet shipment made it a Hawaiian resident.
Overview
Jackson’s chameleons live in cool, humid montane forest and shrubland in central Kenya and northern Tanzania, mostly 1,600–2,400 metres up. They are arboreal, slow-moving, and diurnal, hunting insects and snails with a projectile tongue. Males are the horned sex; females are usually hornless.
The horns
The three horns — one on the snout, one over each eye, bone cored and keratin covered — are for male combat. Rival males meet on a branch, inflate, brighten, and push horn-to-horn, each trying to lever the other off. It is a sexually selected weapon, like antlers.
Live birth
Unusually for a chameleon, the female gives birth to 8–30 live young after carrying them for five to six months — an adaptation to a highland climate where the ground would be too cold for eggs. Newborns emerge in a thin membrane and immediately climb.
Hawaii
In 1972, about three dozen Jackson’s chameleons imported for the pet trade arrived sick and were released into a Honolulu garden to recover. They spread and bred, and their descendants are now established across the Hawaiian islands, where they are a pest — eating native insects and endangered endemic tree snails.
Status
Jackson’s chameleon is Least Concern, common in parts of its native range but declining with forest loss — while thriving as an invasive species in Hawaii.
Jackson's Chameleon: common questions
What are the three horns for?
They are weapons for male-to-male combat, not defence against predators. When two male Jackson's chameleons meet on a branch, they turn side-on, inflate their bodies, brighten their colours, and then engage horn-to-horn, each trying to get its horns underneath the other's head or body and lever, push, or flip the rival off the branch. The loser is the one that is dislodged or that backs down and darkens in colour. Females, which do the choosing but do not fight, are usually hornless or have only tiny bumps, so the horns are a classic sexually selected trait like a deer's antlers, scaled down to a lizard.
Do Jackson's chameleons lay eggs?
No — they give live birth, which is unusual among chameleons (most lay eggs in a hole dug in the ground). A female carries the developing young inside her for five to six months and then delivers a litter of typically 8 to 30 (occasionally more) fully formed babies, each in a thin sticky membrane that it breaks out of and that helps it cling to a leaf. Live birth is thought to be an adaptation to the chameleon's native habitat — cool, wet highland forest above 1,600 metres, where soil temperatures would be too low and unreliable for eggs to incubate successfully. The mother provides no care after birth.
How did Jackson's chameleons end up wild in Hawaii?
In 1972, a Hawaiian pet dealer imported a shipment of about three dozen Jackson's chameleons from Kenya. The animals arrived dehydrated and in poor condition, and he released them into his garden in a Honolulu suburb to recover, intending to collect them later. They dispersed instead, found the climate and vegetation of the Hawaiian uplands very much to their liking, and bred. Their descendants are now established on Oahu, Maui, the Big Island, and elsewhere, sometimes at high densities, and they are considered a pest because they eat native Hawaiian insects, spiders, and — of particular concern — endemic tree snails, several of which are endangered or already extinct.
Can you keep one as a pet, and are they hard to care for?
Jackson's chameleons are one of the more commonly kept chameleon species, partly because captive-bred and Hawaii-sourced animals are available and they are relatively hardy. But like all chameleons they are demanding. They need a tall, well-ventilated, heavily planted enclosure; cooler temperatures than most tropical reptiles (they overheat easily and do best with a night-time drop); high humidity and a way to drink moving water (they usually will not drink from a bowl, only from droplets); strong UVB lighting; a varied diet of gut-loaded insects; and minimal handling, as they are easily stressed. Beginners often lose them to heat, dehydration, or poor husbandry.