Sunday, May 15, 2016

Giant Saguaros: From Tiny Seeds to Towering Titans

When we think of saguaros, we usually marvel at the big ones, the 20 and 40-foot tall gains that have lived for over a century, enormous cacti that make the Sonoran Desert such a unique landscape. But  a saguaro begins, as do all living things, very small. A single saguaro seed is not much bigger than the size of the period at the end of this sentence, glossy and black. Each tiny seed contains all of the information necessary to grow into a forty-foot tall towering titan, if it is fortunate to land in the right place and not get eaten.  

I often search for the smallest saguaro I can find while hiking the desert preserves in and around Phoenix, especially the pea-sized seedlings that have a pair of succulent leaves topped by a soft tuft of spines and two threadlike rootlets that cling to the soil. Birds, mice and squirrels harvest most of these tender morsels before they reach a month old, so the chances are slim to find one at this early stage. The statistics are astonishing but grim:

*An average healthy, mature saguaro can produce more than 150 fruits in one season.

*Each fruit may contain more than 200 seeds.
*Thus, one saguaro can produce over 300,000 seeds each year.
*Over a century of reproductive life, a single large saguaro may bear more than 30 million seeds.
*Out of all those seeds, only one out of a thousand will end up in conditions where there is enough moisture to enable it to sprout.
*Ultimately, only one out of several million seeds will become a full-grown cactus in the wild due to predation of fruit, seeds and you cacti by many different creatures, including humans. Freezing, drought, and flash floods also take their toll on young cacti.
         In the shelter of a "nurse tree" or shrub, usually a Palo Verde or Mesquite, a young saguaros chances are much higher. Shade an moisture will prevent it from getting dehydrated during those tender years. Dispersal by birds that eat saguaro fruit is the most effective for seeds to land in suitable germination and establishment sites, as they deposit them in droppings while perched on tree limbs. Saguaros generally out-live their nurse plants, but they do not parasitize them in any way.
         There is no simple formula by which to estimate the age of a saguaro because they do not have growth rings like woody trees. Aging a saguaro by height depends on location, especially the amount of rainfall they receive. Data from measurements taken of saguaros at three locations in the wild show that at 100 years, height can vary from between 15 and 30 feet. A 1 to 3 inch tall wild saguaro is about 10 years old. At about 25 years, a wild saguaro will be 2 to 3 feet tall. Two hundred years is a long life for these giant cacti.

Late April to early June is the season for saguaro blossoms. the official state flower of Arizona. Each flower blooms for only one night, opening after dusk and remaining open until early afternoon the next day. A new set of flowers blooms for up to six weeks every night, attracting numerous pollen and nectar feeders, including long-nosed bats by night, doves and many species of insects during the day. Most of these creatures also serve as pollinators for the saguaro.

Wild saguaros begin producing flowers and fruit at about 50 years, but this ranges from 30-75 years, depending on available moisture. Flowering age corresponds to between 6 and 8 feet tall. Saguaros begin producing "arms" after 50-70 years, which also increases flower production, since flower buds emerge at the top of each arm.

         A mature saguaro with many arms can weigh up to 9 tons: a hydrated stem weighs about 80 pounds per foot, so a 30-foot tall single-stemmed saguaro may weigh about 2400 pounds. The tallest recorded specimen once lived near Cave Creek, AZ, reported at 78 feet tall before it died in 1986. The current record for the tallest living saguaro is a dwarf in comparison at only 45.3 feet tall and a circumference of ten feet.
         No matter what their size, any saguaro you encounter is a miracle of desert survival.

Friday, February 26, 2016

Coming to Terms with Termites

If we could make a window into the subterranean environment, we would see a world as intricate and alive as what we know above ground. This is the domain of one of our most common household pests, the Desert Subterranean Termite. In the wild, all termites play an important role helping to break down dead plant material and dung, insuring that nutrients are recycled back into the soil. Their tunnels help to circulate air and water in the soils, which is necessary for healthy plant growth. They are also an abundant source of food for lizards, birds and larger insects. In some African and Indonesian cultures, termites are a common snack for people too, usually served roasted and lightly salted. Yum!

More than 2600 species of termites are known around the world; less than 10% of those cause damage to buildings. In the U.S. we have forty-five species; eighteen are found in Arizona, but only four of those species commonly become pests when they feed on man-made structures. Of these, the Desert Subterranean Termite (Heterotermes aureus) is the most pervasive native termite of the Mojave and Sonoran Deserts in California, Arizona and Mexico.

Like ants and honeybees, termites are colonial, with several functional roles or "castes." Each colony begins with a queen and king, who are responsible for mating and producing eggs. Although a newly mated pair needs to care for their first set of offspring on their own, eventually they produce thousands of workers whose duties include feeding and grooming the royal couple, as well as eggs, larvae and each other. The tiny quarter-inch long workers cooperate to build extensive tunnel and gallery systems that reach as far as three meters below the surface and may house up to 300,000 termites. About 10% of a colony develops into sterile soldiers equipped with fierce jaws that can crush other insects, especially ants, that may invade a colony.

During evenings in late summer months, you may notice winged termites, also known as "alates," swarming outside, or if you are unlucky, inside your home. These termites, unlike workers and soldiers, are able to mate and reproduce. If a male and female find each other and a suitable place to burrow into the soil, they will start a new colony. Thousands of alates will swarm from a mature colony each year, but only a few escape the fate of death by predation or other natural causes.

Termites are dependent on specialized bacteria, fungi and protozoans in their gut that are able to digest wood. By sharing food with the rest of the colony, workers also transfer gut organisms to new larvae and each other. This behavior is one way that toxins used for termite control get distributed. Any termite that encounters the toxin will return to the colony, where mutual feeding and grooming will cause the poison to spread throughout the population. It normally takes just a few days for an entire colony to be infected with the toxin and die.

Either you've had them in your home, or you will, but if you can suspend your horror and disgust at the idea of tiny bugs munching away inside your walls, the world of termites is actually quite fascinating. Despite their potentially destructive impact to our homes, termites are critical to the health of our desert ecosystem. You can do your part to reduce the introduction of toxins
necessary to destroy them by creating termite resistant physical and chemical barriers to your house. This way, termites will carry on in their important ecological role in the desert around, but not inside, your home. Some ways you can minimize the likelihood of termites entering your house include:

*Make sure there is no yummy termite food next to your house, which includes any kind of wood, whether it is firewood, crates, building materials or furniture.
*Keep areas next to the house dry and free of irrigation. Termites prefer to forage in moist soils.
*Be sure that floor joints and cracks are sealed and treated with termite repellant before you install wood flooring.
*Do regular inspections around your foundation and interior walls to catch any termite activity before it creates serious damage. Call a certified professional to chemically treat any problems.

For more detailed information on local termite ecology and control, check out the Arizona Cooperative Extension document: Arizona Termites of Economic Importance (2005).

If you are buying or selling a house in Arizona, it is customary for the seller to be responsible for any termite protection that is deemed necessary before closing on a real estate contract. Usually this involves an inspection and a treatment that includes a minimum one-year warranty if any active termites are found.

Saturday, January 2, 2016

Heron Heaven

Great Egret

On any day of the year, if you visit one of the many suburban ponds or waterways scattered throughout the Phoenix suburbs, you will almost surely see one of our most elegant resident birds, a heron called the Great Egret. They are easy to recognize, standing at three feet tall with long dark legs, a slender yellow beak and pure white feathers. If you look more closely, you are also likely to spot several other species of herons: Great Blue Herons, Green Herons and Black-crowned Night Herons are better camouflaged, but share the same habitat. Another white heron, the petite Snowy Egret, about two feet tall with a dark beak and yellow feet, is also fairly common.
Great Blue Heron

If it weren't for Boston tea parties, however, we might not be able to witness the majesty of herons in our suburbs today. A little more than a century after the raucous dockside tax rebellion that ignited the American Revolution in 1773, two Boston socialites, Harriet Hemenway and Minna Hall, started another revolution in 1896 by hosting a series of more civilized gatherings to advocate bird conservation. Brought together over tea and biscuits, more than 900 women organized to ban the massacre of birds for their feathers.

During the late 1800's, the breeding plumage of adult Great Egrets was especially coveted by hat fashionistas. (Egret is derived from the French word aigrette, which means "silver heron." An aigrette is also the term for a decorative head ornament made with feathers.) These birds, and many other species, were nearly driven to extinction by hunters who provided feathers for the millinery industry. Efforts pioneered by the ladies of Boston eventually led to national and international laws that made plume hunting illegal. Egret populations have since made a dramatic recovery. This is one reason why the Great Egret was chosen as the symbol for the National Audubon Society, one of the oldest wildlife conservation groups in the country.

Long before we began building ponds and canals, herons have hunted along the Salt, Gila and Agua Fria rivers that once flowed freely through the Central Valley. Some of the birds are year-round residents; others winter here and return to breeding areas further north during the summer. Along wilder sections of the Gila River south of Goodyear (SW Phoenix), you can see large colonies of herons nesting and roosting in cottonwood and mesquite forests.

Anywhere there are fish, even if it's a small goldfish pond in your backyard, herons are able to detect their favorite food and may soar in for a snack. The Arizona Game and Fish Department, municipal Parks and Recreation Departments and local homeowner's associations assist with enhancing heron habitat by stocking ponds and reservoirs with fish. Although their primary intent is to provide angling opportunities for urban residents, herons and other wildlife benefit from fish stocking. Other ponds are stocked and managed specifically for wildlife, including a peaceful retreat in Glendale's Thunderbird Park at 59th Avenue and Melinda Lane, where special viewing blinds have been constructed for anyone who likes to sit and watch wildlife. If you are as patient and still as a heron, you may witness one catching its dinner.
Herons gather at a pond in north Glendale

Friday, October 16, 2015

Beyond Bermuda

A neatly trimmed lawn is perhaps the most iconic emblem of the American suburban lifestyle. Many people regard a cool patch of green as an essential ingredient of a civilized landscape, a symbol of serenity and order. Whether your favorite turf is in the form of a ball field, playground or a merely decorative feature of your own front yard, lawns are living communities of plants and animals, as well as recreational havens and design elements.

Bermuda Grass

The most common species join local lawns and playing fields is Bermuda Grass (Cynodon dactylon), a tough turf that was imported from southern Africa centuries ago to enhance grazing pastures. In the U.S., the grass is named after islands in the mid-Atlantic ocean that are presumed to have been a stepping stone to their introduction to North America. It is also abundant in southern India where it is called arugampul or doob and has been used for thousands of years as a medicinal herb to aid in healing everything from rashes to diabetes.

Also known as couch grass, devil grass, wire grass and dogtooth grass, this heat-loving plant is both celebrated and loathed for being hearty enough to survive the scorching hot and arid climate of Phoenix. In the same aisles of garden supply centers that sell 50# bags of Bermuda grass seed, there are also multiple chemical treatments available to attempt killing it. Fortunately, or unfortunately, depending on which side you are on, Bermuda grass is extremely persistent, partly due to the facts that roots can drill down more than two meters into the earth and that small fragments of grass can propagate into full plants within weeks. However, Bermuda grass is not tolerant of cold, hence an annual ritual of thatching and over-seeding with ryegrass is practiced every fall by those who wish to toil away at watering, weeding and mowing all year round for the pleasures that green grass provides. While the leave so Bermuda will wither and turn brown through colder months, the roots remain very much alive but dormant, ready to spring forth when soil temperatures rise again.
Kidney Weed

Even in perfectly manicured lawns, there is always more growing between the blades than the favored type of grass. Dozens of plant species thrive on the moisture and fertilizer that lawn cultivation provides. Among them are dandelions, spurge, chickweed, pigweed, lawn parsley and mallow. Most people call the interlopers "weeds." On a professional playing field, such varied textures may cause interference in the game, but if your main aim is aesthetics, you may want to consider nurturing a plush carpet of kidney weed (Dichondra repens) or cheerful heart-shaped leaves and bright yellow flowers of wood sorrel (Oxalis corniculata). And everyone loves searching for good luck in a patch of clover!
Wood Sorrel

Lawns also attract wildlife, both predators and prey. Cottontails feast on the grass; owls, coyotes and bobcats feast on cottontails. The larvae or caterpillars of furry orange butterflies called "fiery skippers" chew on the leaves, attracting all kinds of birds that forage for juicy grubs. Even more birds relish the times of year when people scatter fresh grass seed to primp up a sparse lawn. Numerous other species of uninvited grasses also make their homes in Bermuda turf. If left un-mown, a lawn can rapidly become a thigh high meadow full of wildflowers and insects. In Africa, Bermuda grass is part of the vast savannah that supports herds of rhinos an impala. Of course, this is not what we strive for in suburbia, which is why I've chosen to trade in my patch of Bermuda for artificial turf!

Monday, June 29, 2015

Flame Skimmer 

Bugs bigger than birds might sound scary, but most folks agree that dragonflies are more mesmerizing than fearsome. One of our local dragonflies, the Giant Darner, is the largest dragonfly in North America, with a five inch wingspan, and an equally long body. That's just a tad larger than the wingspan of some of our common hummingbirds! Although they are carnivorous, there's no need to worry: dragonflies don't sting or bite humans, but feast on bugs that do annoy us, like mosquitoes and gnats.

Since these fascinating insects are in the taxonomic order Odonata, the sport of dragonfly watching is called "oding." If you are beginner in the sport, you may just want to learn the difference between two major groups, or suborders, the damselflies (Zygoptera) and the dragonflies (Anisoptera), which can be distinguished at a glance. Dragonflies hold their wings horizontally at rest; the more slender damselflies fold their wings over their back when perched.
Powdered Dancer

Dragonflies and damselflies were not granted official common names until 1996. Before that, they were known mostly by their Latin family or species name; at least two dozen families and more than 5,500 species are currently recognized world-wide. A dozen or so species are commonly seen around suburban Phoenix, and more than a hundred are known throughout Arizona.

None of them can walk, but all are exceptional fliers, able to cruise at about 10 mph on average, and put o 30 mph, beating their wings at thirty times per second. They can move in any direction as well as hover, inspiring aeronautical engineers to study them in detail for clues to better mechanical design.

However, it is the monstrous looking aquatic larval stage that earned the group the common name "dragon" and the Latin name, Odonata, which means "toothed," for an over sized spiny jaw that extends like an arm to grab prey. Dragonfly larvae, also known as nymphs, live in freshwater ponds and streams where they hunt other insects, tadpoles and small fish. You can easily spot a damselfly nymph by the three feathery looking gills at the tip of their abdomen or "tail" and by the way they wiggle their body as they swim through water. The gills of dragonfly nymphs, in contrast, are inside their body. They move in quick bursts by squirting water out the end of their abdomen like miniature underwater jet boats.
Exuvia or husk of larva 

When a larva is ready to transform into an adult, it crawls out of the water, cracks open its skin right down the middle of its back, and slowly crawls out to begin a few weeks or months of life on the wing. In most species, males and females look very different, and like birds, the males are usually more brightly colored than the females. Male dragonflies are also territorial, and will chase off other males that intrude on their favorite stretch of stream or shoreline, but welcome females. Once he does find a mate, he latches onto her neck with special claws at the tip of his abdomen. The pair mate in flight, making a "heart" or "wheel" shape with their long abdomens. He will continue to guard her so that she can't mate with other males.

To complete the life cycle, a female will lay between 500-2000 eggs. If you see a dragonfly dipping the tip of its abdomen on the water while in flight, it is a female laying her eggs, one by one. Damselflies lay their eggs in the stems of plants where the hatched larvae can easily crawl into the water. Nymphs live under water between one and five years before emerging in their full glory as winged dragons and damsels. Hot summer days are the best time to spot dragonflies cruising desert washes and urban ponds where they patrol for meals and mates, so now is the time to get out your binoculars and do some doing!

Learn more about local dragonflies at a website created by ASU professor Pierre Deviche and dedicated to Arizona dragonflies.

Sunday, May 3, 2015


Sotol (Dasylirion wheeleri) has become a staple of suburban landscapes in southwest desert communities because of its beautiful form, drought tolerance and easy maintenance. Archaeological records show that the plant has been popular with people for more than 10,000 years. To Ancient Puebloans, though, the plants were not merely ornamental. They collected and used the leaves for fiber to make mats and baskets. Young tender stalks and roots were roasted for food. Dried sotol stalks were used as fire ploughs, a method of fire making in which a dry stalk is rubbed in a wooden trough until the friction makes a hot cinder. Sweet pulp from the sotol "heart" was used to make a fermented drink much like mescal or tequila is made from agave. This drink is still popular in some parts of Mexico.

Perhaps the most stunning feature of sotol is the huge flowering stalk that emerges each May from the center of a mature plant. After a couple weeks of daily measurable growth, the sotol in our neighbor's yard finally bloomed last year. The sixteen-foot tall stalk rose from the giant rosette of sawtooth-edged leaves, luring swarms of honeybees and tiny colletid bees that came to gather pollen. I've been amazed by the rapid growth of flowering stalks for over a decade, but did not realize until recently that sotols are dioecious, meaning that there are botanical equivalents of male and female plants.

Male plants bear long curly bunches of pollen-producing flowers, which sort of look like Cheetos, but without the orange dye. The sheer magnitude of the stalk and all of that pollen is truly astonishing. Likewise, females bear thousands of seed-producing flowers. Although the bees harvest prodigious amounts of pollen, they do not visit the female flowers because there is no nectar to attract them. The females must depend on wind to deliver pollen for fertilization. From a distance, you can tell the two types of stalks from one another simply by noticing the presence or absence of insect activity: male stalks are swarming with bees; female stalks may have a bird perched on top, but no bees.

Despite the fact that there are thousands of sotols growing in the Phoenix suburbs, you are unlikely to find one in nearby desert preserves. The natural habitat for sotol is much higher than our fair city, in scrublands and grasslands over 4,000 feet in elevation. They are most common in the Chihuahuan Desert, which extends from southeastern Arizona through New Mexico to Texas and Northern Mexico.

If you grow sotol in your yard, you can save yourself or your landscaper from hassling with the spiny leaves by letting it grow naturally rather than "pineapple-izing" the base. Although this practice may have been a way for ancient people to harvest leaves for fiber, there is no need to remove them otherwise. Better to sit back and enjoy a shot of sotol, or just admire these hearty and majestic plants in you desert landscape.

Saturday, February 7, 2015

What a Lizard Wants

A pair of Side-blotched Lizards  photo by Rick Halliburton 

When a lizard goes searching for real estate, their dream home has many of the same features we may have on our list: Beautiful landscaping, a sunny spot to relax in when it's cool, a shady spot to hang out when it gets hot, a neighborhood that is safe from predators and easy access to good food. They're not going to list granite countertops, but a large granite boulder to bask on would make a lot of lizards very happy.

Recent surveys in the Phoenix urban area by reptile biologists at Arizona State University have shown that, indeed, all fourteen native species of lizards in the area seem to prefer the same areas occupied by prime real estate. In an article called "Rich Lizards," PhD student Jeff Ackley and colleagues report that the diversity of lizards in the urban area is highest in more affluent neighborhoods. They call it the "luxury effect." Characteristics that tend to increase value for real estate also make for better quality lizard habitat. This includes: closeness to desert preserves, greater diversity of plants, more natural open space and less asphalt. Affluent neighborhoods also tend to have larger yards with more native plants and fewer lawns. A side benefit of all these features is that air temperatures are slightly cooler, especially during summer nights. This is because there is more shade during the day and a reduced "urban heat island" effect at night.
Regal Horned Lizard   photo by Kathy Darrow

However, each species of lizard has particular wants and needs that may limit where they can thrive, just as we humans all have various things that keep us most comfortable. What a Regal Horned Lizard needs most, for instance, is ants, and around here, a certain species of seed harvester ant: Pogonomyrmex rugosus. These ants prefer open flat areas where there are plenty of native seeds to harvest, so very few populations of Regal Horned Lizards have survived in the urban area. Flat ground is the first to go when development is planned.

Only two of the ten Phoenix desert preserves that have been surveyed have more of what Horned Lizards want: Deem Hills and Cave Buttes have enough flat ground to support healthy harvester ant populations. You will most easily find these reddish ants by looking for their nest holes, which are usually near the center of a 3-6 foot wide gravelly circle. After summer rains is the best time to watch harvester ants at work gathering seeds from afar, which they tore in special chambers below ground. Horned Lizards will seek out an active colony and snatch them up with their short, fat, sticky tongues. One of the ways biologist can tell if there are horned lizards around is by finding their fecal pellets (aka poop) nearby, which are masses of ant parts a couple of inches long.
Desert Iguana  photo by Brian Sullivan

What do other kind of lizards want?
*Desert Iguanas want creosote bushes to feed on and lots of space to run.
*Chuckwallas gotta have crevices to climb into, just the right size, so they can take a deep breath and wedge themselves in. Plus, they are picky eaters: palo verde, globe mallow and showy goldeneye are some of their favorite foods.
*Tiger Whiptails like rodent burrows to dodge into for shade and protection from predators.
*Ornate Tree Lizards want trees to climb, but vertical walls will do, and thus, they are the most abundant type of lizard in the urban area.
Ornate Tree Lizard photo by Kathy Darrow

What all lizards really want, though, is to be left in the wild with room to roam, places to hide and where it's easy to find their favorite foods. you can add a little luxury to an urban lizard's life, and maybe even boost your own real estate value, by planting native trees and shrubs in your yard, plus a large boulder or two for basking.

To learn more about local lizards, check out the website for "A Field Guide to Reptiles & Amphibians of Arizona" by Thomas Brennan and Andrew Holycross: