Africanized Honey Bees
In 1993, a strain of particularly vicious African honeybee---escapees from a lab in Mexico---crossed the Texas border. In the years since, the bees bred with the docile European honeybee and colonized Arizona. Each person's tolerance determines the amount of stings needed to cause illness or death. Africanized bees swarm easily and attack faster than European honeybees. Upon encountering a nest, leave immediately and, if possible, get into an enclosed area like a car.
Roughly the size of a medium-sized dog, bobcats---two varieties live in Arizona---jump 12 feet, eat small mammals and usually leaves humans alone. Vaguely resembling overgrown housecats, they have thick tan coats with black spots and short, black-tipped tails.
On the other hand, the cougar or puma (or a half a dozen other names) will attack humans and pose a threat to those hiking alone. The tawny furred cat grows to be as big as a German shepherd. Its belly is white and its tail black-tipped. Cougars commonly eat deer, elk, javalina and small mammals.
Coyotes are extremely versatile; they eat whatever comes their way, from plants to fawns. Coyotes look like a small wolf or a mixed dog, growing to about two feet tall on all four paws with rust-colored markings and a cream belly. Coyotes are secretive and are rarely seen, but often heard. Howls, yips and yelps alert you to their presence. Unless diseased, coyotes present no threat to humans.
The javelina looks like a small wild pig, but evolution made them a naturally wild, hoofed-rodent which just happens to resemble a pig. Javelina travel in herds of up to 20 members, relying on each other for survival. You may come across them during your travels in southern or central Arizona. While they may look harmless, javelina know how to use their tusks to defend themselves.