Sonoran Desert

Poisonous and venomous organisms both use toxins, but in very different ways. Poisonous creatures and plants use their toxins to defend themselves from predators.¹ They are often more passive than venomous creatures, releasing their toxins only when they are touched, attacked or eaten.² These unappetizing organisms are often incapable of producing toxins themselves.³ Pipevine Swallowtail Butterflies, for example, ingest the toxic chemical of its host plant, the California Dutchman’s-pipe as caterpillars. This toxin remains in the adults, who in turn pass this toxin on to their eggs.⁴ Many poisonous creatures use color and patterns as a warning to predators. The brightly colored Convergent Lady Beetles use aposematic coloration⁵,⁶ as a warning of the toxic chemical in their blood.⁷ The Queen Butterfly is not the only butterfly to use bold orange and black patterning as a defense; the Queen, Viceroy and Monarch butterflies - all poisonous and distasteful - exhibit Müllerian mimicry,⁸ a type of mimicry where multiple species share warning colors to help protect themselves from predators.⁹ While humans are unlikely to be tempted by lady beetles or butterflies, the appealing hallucinogenic properties of the Sacred Datura do occasionally lead to life-threatening poisonings.¹⁰ Symptoms of ingesting Sacred Datura can include blurred vision, difficulty breathing and auditory and visual hallucinations.¹¹ These effects made Sacred Datura an important part of the rituals of many indigenous peoples of the American Southwest.¹²,¹³

Venomous creatures usually make their own toxins, and must deliver these toxins through a wound:¹⁴ a Stripe-tailed Scorpion’s “essentially painless” sting,¹⁵ the pinch of a Common Desert Centipede’s pincer-like appendages,¹⁶ or a bite. The Sonoran Desert is home to numerous reptiles that deliver their venom through bites. Although its fangs are unusually short,¹⁷ the dangerous neurotoxin in the venom of the Tiger Rattlesnake makes its venom the most toxic of any rattlesnake species.¹⁸ The venom of the Arizona Coral Snake is also a neurotoxin, although not as potent as that of North America’s other two species of coral snake.¹⁹ The Gila Monster, one of the world’s few venomous lizards,²⁰ does not inject its venom through fangs. Its venom is produced by a row of glands in its lower jaw, and then chewed into its prey²¹ (or an attacking predator)²² with the lizard's grooved teeth.²³ Bites of these three shy, elusive reptiles are unlikely for humans, unless the reptiles are intentionally handled.^24,25,26 Although arachnophobes may also expect a nasty bite from the Desert Blonde Tarantula, these docile spiders pose little threat to humans,²⁷ with a level of venom comparable only to a bee sting.²⁸ (Surprisingly, the hairs of the tarantula are what human handlers should worry about! The specially designed barbed hairs on the abdomen of the tarantula can be very irritating²⁹ and, if inhaled, can require hospitalization.)³⁰

The many defensive strategies of the poisonous and venomous organisms of the Sonoran Desert demonstrate the beautiful ingenuity of the natural world, and serve as an important reminder that plants and animals are often best observed, and not touched!

The Saguaro Cactus, an iconic symbol of the American west, is only found in the Sonoran Desert. Although mature cactuses can stand over 40 feet (12m) tall, Saguaros are very slow growing.¹ Sheltered under protective nurse trees, it takes eight years for the Saguaros to grow their first 1 to 1.5 inches (about 2.5 - 4cm). Saguaros do not begin to flower until 35, and do not grow their characteristic branches for 50 to 100 years, depending on precipitation levels. Specially adapted to their sometimes harsh desert environment, Saguaros have 5 foot (1.5m) long tap roots, a waxy coating to slow water loss,² and pleats that can expand or contract like an accordion to accommodate sudden influxes of water. Saguaros are vital members of the desert ecosystem, playing an important role in the lives of many desert mammals and birds.³ These desert sentries flower and fruit during the driest and hottest months of the year, providing moisture and nutrients at a time when sustenance is in short supply.⁴ Saguaros have, in turn, come to depend on some of these species for pollination and seed dispersal.

Saguaro flowers bloom at night and remain open until the following afternoon.⁵ Their creamy petals and alluring scent attract their primary nocturnal pollinators: the Lesser Long-nosed Bat.⁶ These endangered, migratory bats⁷ have brush-tipped tongues as long as their bodies that they use to lap up nectar. As they drink, their fine-haired heads are covered in yellow Saguaro pollen, which they carry from flower to flower.⁸ During the daylight hours, the Saguaro is pollinated by White-winged Doves. The western population of White-winged Doves synchronizes their migration and breeding cycle with the flowering and fruiting of the Saguaro.⁹ After pollinated flowers transform into seed-rich fruits, White-winged Doves continue to feed, occasionally dispersing Saguaro seeds. Saguaro seeds cannot survive the Dove’s digestive system,¹⁰ but may be dropped below suitable nurse trees as Doves feed seeds to their young.¹¹

With its Seuss-like, 10 to 20 foot (3 - 6m) tall profile and brilliant red flowers, the Ocotillo is another striking member of the Sonoran Desert plant community. Ocotillos serve as an important source of nectar for migrating hummingbirds, blooming even in the driest of years when other nectar sources are scarce.¹² The Hummingbirds’ long and slender beaks fit perfectly into the Ocotillo’s tubular flowers, making them excellent Ocotillo pollinators.^13,14 Carpenter Bees use a different nectar-gathering strategy: they are thieves! Carpenter Bees slit the flowers at their base, and lap out the nectar. However, it has been observed (outside of the Sonoran Desert) that in the process of their thievery Carpenter Bees manage to be quite effective pollinators.¹⁵

Both the Saguaro Cactus and Ocotillo are threatened by the climate crisis.^16,17 If these two plants disappear from the Sonoran Desert landscape, the brilliant web of life that they each support will unravel. The loss of these desert denizens would also represent an enormous cultural blow to the indigenous Tohono O’Odham people, who used ocotillo to construct their traditional dwellings,¹⁸ still uphold the sacred tradition of harvesting Saguaro fruits,¹⁹ and view the Saguaro as “respected members of the Tohono O’Odham tribe.”²⁰

Herds of javelinas, highly social, vocal and quite smelly, are a common sight in the Sonoran Desert.^1,2 Although they may resemble the wild hogs and pigs introduced to the Americas by European colonizers, Javelinas are native to South America and the American Southwest, and are in fact members of an entirely different family of mammals: the peccaries.^3,4 Javelinas can breed all year long and have two litters of usually two young per year. Newborn javelinas weigh about one pound,⁵ and are often called “reds” due to their distinct coloring.⁶ Young javelinas are able to follow their mothers shortly after being born, are weaned around six weeks, and gain their adult coloring in three months.⁷ Javelinas are omnivores, eating a varied diet high in desert plant life; they will tear apart the pads of prickly pear cacti and use their hooves to smash hedgehog cacti.⁸

Cactus Wrens are common throughout the Sonoran Desert,¹ and the Cornell Lab describes their raspy song as the “quintessential sound of the desert.”² These bold wrens can often be spotted perched on prickly-pear cacti. Their diet consists primarily of spiders and insects. Grasshoppers are a favorite for hungry nestlings, who can eat more than 14 grasshoppers each day. Cactus Wrens can also eat cactus fruits. They nest year round, constructing football-sized nests three to ten feet off the ground in desert vegetation. Cactus Wren numbers have declined over the past half century, and precipitous declines are possible in the next twenty years. To protect this charismatic desert dweller, their habitats must be protected against urban and agricultural expansion.^3,4