Category: velvet mesquite

Living Jewels that Seek Fire and Eat Wood

Among the most important components that power the machinery of forest life are insects – beetles in particular play crucial ecological roles in forests.  One of the largest beetle families is the Buprestidae, represented by nearly 16,000 species. These creatures are known as “jewel beetles” due to their family’s spectacular array of iridescent colors and patterns. The insect pictured above is one dazzling example, native to the coniferous forests of the Rocky Mountains.

One of the world’s largest jewel beetles is Euchroma gigantea, native to Amazonia. These insects can measure over two inches in length. This is a mounted specimen from Brazil, part of the author’s collection.

In most living organisms, iridescence is enabled by pigmentation. Jewel beetles are different – their iridescence is structural in origin; microscopic texturing on the surfaces of their exoskeletons selectively reflects specific frequencies of light while absorbing others.

Most jewel beetles lay their eggs on dead or dying trees. Once the eggs hatch, the beetle larvae go to work, chewing their way through the wood. They leave a maze of tunnels in their wake. Some species of jewel beetles will lay their eggs only on freshly burned trees. These specialized insects are known as pyrophiles (literally, “fire loving”). Forest fires create a nearly instant Shagri-la for them.

The larvae (or grub) of a jewel beetle found inside a section of velvet mesquite wood. These larvae are often known as flathead borers due to the shape of their heads. The tunnels that such larvae create in dead wood are of great importance to forest ecology.

Pyrophilous jewel beetles have evolved specialized extra-large wing muscles to enable long distance flights to wildfire sites. These beetles have a way of finding burned trees that borders on the miraculous…

One of the buprestid beetles native to velvet mesquite bosques in southeastern Arizona. Note the heavyset, thickened body of this insect, a specialized morphology that allows room for large, powerful flight musculature.

When they fly, these beetles hold their bodies at an angle, in order to orient their underside to the direction of travel.  Minuscule texturing on the ventral side of the insect’s thorax functions mechanically in response to incredibly faint traces of infrared radiation (heat). Infrared radiation causes a pressure differential to occur in the thorax texturing. This fires neurons, sending a message to the beetle’s brain. The message says “fly in this direction and you will find a smorgasbord of freshly killed trees to provide food for your offspring.” What is even more amazing is that these insects can detect the heat given off by fires at distances up to fifty miles!  (research conducted by Dr. H.P. Bustami and associates at the University of Bonn [in Germany] brought this astounding facet of jewel beetle biology to light.)

A living jewel adorned with iridescent gold flecks and shimmering purple-sapphire elytra, this native buprestid inhabits local mesquite bosque habitats.

This relationship between forests, fire, and beetles has been going on for countless millennia. However, people often take a dim view of beetle larvae drilling tunnels in trees, claiming that this ruins otherwise “valuable” wood. Such anthropocentric views are myopic, for they exclude the needs of all other living things and turn a blind eye toward the ecology of forests. Jewel beetles benefit forests as agents of decomposition; the tunnels that their larvae bore in dead trees provide important open pathways for other insects and for the introduction of fungal spores. The tunnels facilitate the exchange of gasses in the wood and furnish the perfect moist, insulated, dark environ for fungi to take hold. Fungi are crucially important to living trees, to the health of the soil, and for their leading role in the recycling of nutrients via the decomposition of dead trees and other organic detritus. No forest on Earth can exist without fungi and decomposition.

This maze of tunnels was bored by jewel beetle grubs in a dead limb on a living velvet mesquite tree. Read the text above to discover why these tunnels are so beneficial to forest ecology.

This is a limb that was cut from the same tree as the one in the preceding image. However, this limb was cut when it was alive. Note the scarcity of holes and tunnels. Most jewel beetles lay their eggs only on dead wood, but there are a few exceptions to this rule.

Here in the desert southwest, jewel beetles are usually easy to find almost any place where trees are present. I have also found them rather often in upland desert habitats – areas that are essentially treeless. Buprestid beetles fly into these places seeking nectar and pollen meals from the wildflowers and flowering shrubs that grow there. Thus, they provide another important ecological function by acting as pollinators.

A Fascinating New Bird Appears

A few months ago, an unfamiliar bird call became part of the daily biophony here on our home acreage in the Middle San Pedro Valley. As an ever-curious naturalist, I had to know what bird was uttering those strange calls. My wife, Kathleen, had noticed it too. The bird called frequently in the early and late hours of every day, taunting us with its unique, three-note call.

Binoculars in hand, I went looking. I slowly approached in the direction of the sounds, looking patiently and carefully. The local habitat consists of a mature forest of velvet mesquite trees. The sound seemed to be originating up in those trees, but no matter how much I searched, the bird remained unseen. Most often, as I approached too closely, the mystery bird would exit stage left and start calling from a new, more distant location. I tried on another day, and another. Every time, the maker of the calls remained elusive and sequestered.

Velvet mesquite bosque, the woodland where the mystery bird appeared. This is an image from the summer months.

One morning, after hearing the unseen bird again, Kathleen and I decided it was time to explore the  xeno-canto website. I know of no better website when it comes to searching for bird sounds; readers can find it here:  https://www.xeno-canto.org  

I had a growing hunch that we were hearing a thrasher…when we listened to the recordings of crissal thrashers, both of knew that the enigma had been solved.

The crissal thrasher visiting our bird bath on a cold morning when the water had frozen solid. Crissal thrashers average 11 1/2 inches in length. This species is known to form pair bonds (in preparation for the spring breeding season) as early as January. Just two days ago, I noticed that our thrasher had found a companion…

Why hadn’t I seen the bird? I had been looking up in the trees when I should have been looking down, at or very near ground level. The bird seemed to have the ability to “throw” its voice, making the calls sound like they were coming from above. Once we had learned the identity of the bird, we realized that we should have been searching for it on the ground, not up in the trees. Now, we see the thrasher every day as it hides beneath graythorn bushes, foraging for food.

Graythorn is indeed very thorny. Meant to discourage consumption by mammals, the thorns protect the plant, but when it comes to birds, these thorns are an attraction. They spell security from predators, especially raptors.

Crissal thrashers spend much of their time beneath thick cover, using their long, decurved bills to dig and rake away soil and duff in search of insectivorous food. Locally, these birds appear to have a very strong connection with graythorn bushes. Graythorn (Ziziphus obtusifolia) is the most common understory shrub in local mesquite bosques. It grows dense, tangled, thorny foliage, furnishing the perfect place for shy birds to seek cover in. I cannot overstate the ecological importance of these plants with respect to bird life. Many species of birds hide in graythorns, feed from the plant’s abundant berries, or nest deep within its thorn jungle of tangled branches.

At the time of this writing, the graythorn bushes outside my windows are in full flower. The blossoms are minuscule.

After the flowers have been pollinated, berries grow on the graythorn bushes, providing an important food source for many local birds and mammals.

This winter, the Middle San Pedro Valley has been inundated with unprecedented numbers of white-crowned sparrows. There are hundreds on our land every day, and in many other places as well. I cannot walk by any graythorn bush without flushing a throng of white-crowns from within. Like the thrasher, they forage on the ground and use graythorns for cover. Security is imperative to all small birds here, for bird-hunting Cooper’s hawks are present almost every day. 

A HOPEFUL NEW YEAR, WINTER IN THE SAN PEDRO VALLEY, AND AN ARTIST’S VIVID EXPRESSION OF THE RIVER

The promise of coming  vaccinations, a new president, and the start of a new year have me full of hope… a state of mind that had faded considerably during 2020, a year marked by tragedy, social division, societal unrest, and a steadily worsening global pandemic. 

Here in the Middle San Pedro Valley, the season of winter is at hand, although the use of a term like “winter” in a place like this is a stretch of the word. The coldest temperature I have ever experienced here was only 8°F., and snow rarely falls in the valley floor. The image above was taken on a winter morning when a rare  blanket of fog had smothered the riverbottom forest with its cool, moist embrace. Fog is almost as rare as snow here. When fog does occur, it is a very transient affair, for desert fog most often dissipates into invisibility very quickly as the day warms.

A full moon casts its light on a stand of winter saguaros.

A few years ago, five inches of fresh snow fell overnight, gracing our bosque with a mantle of gleaming, sparkling white. I could not resist taking an early morning walk in order to read the very best of nature’s newspapers, for the goings on of every bird and mammal were written plainly in the snow. I encountered fresh tracks of various songbirds, quail, coyotes, a raccoon, mule deer, javelina, mice, cottontails, jackrabbits, and more. Following a set of roadrunner tracks (they are quite distinctive) I came across a sight I had never seen before: a roadrunner perched in a snow-covered mesquite tree.

I met with this well-chilled roadrunner perched in a velvet mesquite tree on a snow-graced morning.

Nature has forever been a source of inspiration for artists. There are scenes along the San Pedro River that could captivate any artist’s mind. Last month, an unforgettable gift arrived in our mail, an original painting crafted by none other than my brother, Rick. He and I had spent some time hiking in the riverbottom woodlands one fine spring day, when the river was alive with color and light. We stopped for a break at one of my favorite spots, a place that left its mark in my brother’s memory. Rick captured the essence of that place beautifully in this painting. What a gift!

“San Pedro Reverie,” by Rick Waldt.

Rain Graces a Thirsty Desert and Four-footed Winter Company

For the past three months, hardly a drop of rain has fallen here in the Middle San Pedro Valley. This is, after all, a desert region, or nearly so – deserts are defined as areas that receive less than ten inches of precipitation per year. Here, we get a tad more than that. 

A typical rural driveway in the Middle San Pedro Valley; no street lights, no signs, and most of all NO PAVEMENT.

When the skies turned darker and darker shades of gray a few days ago, I was overjoyed. The land – and its life – has been under duress in southeastern Arizona. The past summer “monsoon” season yielded very little rain. So, when it finally began to rain earnestly on, of all days, my birthday, it felt like an exceptionally wonderful gift. As I stepped outside at dawn that morning, the air bore the rich, humid smell of rain and earth and wet leaves. I drew in big lungfuls, savoring the feel, the coolness, the dampness. For most Americans, rain is no big deal, a common part of life. Here, it is always something to be reverently grateful for.

After the rain, the floor of the mesquite bosque (Spanish for the word “forest” or “woodland”) was covered with millions of tiny velvet mesquite leaves.

The ground had changed color in two ways; it had turned darker  from the thorough soaking, and had also turned green, carpeted with millions of minuscule velvet mesquite leaves that had been unleashed from the trees by the pelting raindrops. The cyclic path of nutrients from soil to trees and back to the soil lay exposed at my feet, exemplified and accelerated by the rain.

The leaves of velvet mesquite are very small, but they grow in multitudes on the trees, providing a crucially important component of this hot, dry desert ecosystem: shade.

A few hours after dawn, a group of mule deer appeared. They are part of a small herd that has taken up residence in the surrounding mesquite bosque for the past several years. We always welcome their company and never consider them as our “guests,” for they and their kind have been here long before us or our forebears. If anything, we are honored to be guests in their home.

A group of mule deer appeared not long after the rain, foraging on mesquite pods and pigweed (Amaranthus palmeri).