The small desert hairy scorpion is the only scorpion in the monument that is dangerous to humans.
Along with the insects, other arthropods (jointed-leg creatures with exoskeletons) find their home in the desert. The arachnids (eight-legged arthropods) include spiders and scorpions. Of the former, the NORTH AMERICAN TARANTULAS are famous for their large size and formidable appearance, which have given them the wholly undeserved reputation of being dangerous to humans. The really dangerous creatures are the SCORPIONS, whose long, flexible tails bear a poisonous stinger at the tip. Several species are found in the monument; but only the small, straw-colored scorpion has venom known to have been fatal to humans. The other scorpions found in the area can inflict painful stings, but with only localized and rarely serious effects.
The Colorado River toad is exceeded in size among U.S. toads only by the giant toad of south Texas (and Mexico).
Amphibians
As might be expected, amphibians are scarce in the monument because of lack of permanent water. The few springs and seeps, however, furnish excellent breeding places for several species of amphibians. Best known among these are the RED-SPOTTED TOAD, LEOPARD FROG, and CANYON TREEFROG, the latter common near Manning Camp. A spectacular desert amphibian and the second largest toad in the United States, is the huge COLORADO RIVER TOAD, sometimes found near residences in the evening when outdoor lights attract swarms of insects.
Reptiles
Except for small lizards, reptiles are not much in evidence in the monument. Nevertheless, they are present and are important in the various plant-and-animal communities in which they live. Almost all lizards are insectivorous, and along with birds and other insect-eaters help to keep the number of insects within bounds. A notable exception is the GILA (HEE-lah) MONSTER, (See [appendix] for scientific names of reptiles) largest of the lizards found in the United States. (It is one of the world’s two poisonous lizards, and the only one found in this country.) The gila monster is especially fond of bird eggs, and also eats nestlings and small rodents, obtaining necessary moisture from their body juices. These food habits are quite similar to those of the several species of snakes found in the monument, the majority of which are perfectly harmless to humans.
The short-horned lizard, more cold-tolerant than the desert horned lizard, ranges from the foothills into the mountain forests of Saguaro.