Colophon

The animal on the cover of Python Data Science Handbook is a Mexican beaded lizard (Heloderma horridum), a reptile found in Mexico and parts of Guatemala. It and the Gila monster (a close relative) are the only venomous lizards in the world. This animal primarily feeds on eggs, however, so the venom is used as a defense mechanism. When it feels threatened, the lizard will bite—and because it cannot release a large quantity of venom at once, it firmly clamps its jaws and uses a chewing motion to move the toxin deeper into the wound. This bite and the aftereffects of the venom are extremely painful, though rarely fatal to humans.

The Greek word heloderma translates to “studded skin,” referring to the distinctive beaded texture of the reptile’s skin. These bumps are osteoderms, which each contain a small piece of bone and serve as protective armor. The Mexican beaded lizard is black with yellow patches and bands. It has a broad head and a thick tail that stores fat to help the animal survive during the hot summer months when it is inactive. On average, these lizards are 22–36 inches long, and weigh around 1.8 pounds.

As with most snakes and lizards, the tongue of the Mexican beaded lizard is its primary sensory organ. It will flick it out repeatedly to gather scent particles from the environment and detect prey (or, during mating season, a potential partner). When the forked tongue is retracted into the mouth, it touches the Jacobson’s organ, a patch of sensory cells that identify various chemicals and pheromones.

The beaded lizard’s venom contains enzymes that have been synthesized to help treat diabetes, and further pharmacological research is in progress. It is endangered by loss of habitat, poaching for the pet trade, and being killed by locals who are simply afraid of it. This animal is protected by legislation in both countries where it lives.

Many of the animals on O’Reilly covers are endangered; all of them are important to the world. To learn more about how you can help, go to animals.oreilly.com.

The cover image is from Wood’s Animate Creation. The cover fonts are URW Typewriter and Guardian Sans. The text font is Adobe Minion Pro; the heading font is Adobe Myriad Condensed; and the code font is Dalton Maag’s Ubuntu Mono.