There has been a sudden and tremendous eruption of small beetles in the local mesquite bosque. A dense, tall understory of pigweed, (Amaranthus palmeri) covers the floor of the woodland, an exuberant growth enabled by recent monsoon rainfall. When I walked into these plants this morning, curtains of tiny beetles took flight from the pigweed at my every step, thousands upon thousands rising upward like a reverse blizzard.
The leaves of the pigweed plants had become dotted with countless small holes during the last two days. This morning, the plants revealed that an orgy of feeding had taken place during the night. Literally all of their leaves had been reduced to a ghostly remnant of reticulated veins with no leaf tissue left in between. Every plant, everywhere I looked – consumed overnight.
Acres and acres of bosque understory were fed upon by an almost inconceivable number of small insects. The plants looked almost shredded.
A pigweed leaf after the night’s heavy feeding spree.
Naturally, I had to know what these beetles were. They were diminutive, measuring around 4-5mm in length. Up close, the beetles were beautiful, sporting brightly colored, broad white bands running lengthwise across their shiny black elytra. After some research, I learned that they were known as “pigweed flea beetles,” Disonycha glabrata. Their ecology entails a close relationship with specific host plants – they will feed only on plants in the genus Amaranth. I have witnessed dense growths of pigweed during most of my summers here; I had noticed these beetles in prior years, but never in such spectacular abundance. Why had their population so suddenly rocketed this year? I can only guess. Perhaps this year’s rains were perfectly timed at just the right intervals and in perfect amounts to encourage such an event? Maybe it has something to do with their predators…or some other mechanism?
A pigweed flea beetle, Disonycha glabrata.
When insects erupt in large numbers, people are often quick to react with alarm and negative attitudes. Yes, they shredded an entire forest understory – but was that a bad thing? Or simply natural change? It is not our place to pass judgement on what happens in the natural world. Both the beetles and their host plants are native constituents of this ecosystem. So, I do not necessarily think that what has happened is somehow wrong or alarming, but it is interesting.
I found another creature wandering in the pigweed last week – a young adult Sonoran Desert Tortoise! We see these reptiles rarely here in the bosque; they are more partial to nearby upland desert habitat types. This one’s carapace was between 9 – 10 inches long, and like most of its kind, it was cautious, slow-moving, and appeared unfazed by my presence.
The Sonoran Desert Tortoise that I discovered resting peacefully under the trees. This reptile and its close relatives have recently undergone taxonomic revision – to scientists, it is currently known as Gopherus morafkai.
The tortoise’s powerful front legs are clad in rows of thick, hard scales that assist in digging and may help the turtle resist serious injury from predators. When threatened, the tortoise tucks its head in and then covers its front with these remarkably well-armored legs.
A few days ago, I went out on a walk with a naturalist-friend. He shared a special area with me, a mature mesquite bosque with a remarkably rich, lush understory. I was deeply touched by the feel and presence of this almost subtropical woodland. The image below provides some insight into the kind of verdant growth that this “desert” valley is capable of hosting.
A jungle-like wall of vining plants drapes over young trees and shrubs in one of the most lush, beautiful velvet mesquite bosques I have ever seen. Just beyond the reach of this image was a barbed-wire fenceline. On the far side of the fence, cattle grazed – the ground under that part of the forest had been virtually wiped clean, transformed into a deeply impoverished world with respect to native plants and wildlife. Mesquite bosques as rich and fecund as this one have become very rare – cattle are commonplace. How is this right?
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A few evenings ago, an uncommon view from my desk window engendered delight and a deep feeling of gratitude. The scene encompassed a wild mesquite bosque, standing tall and green in summer’s refulgence…a gentle, drizzling rain was floating its way to the ground, suffusing the air among the stout trees with the magic of a fine mist, colored soft in fading light. The land was coming alive, replete with the promise of sprouting plants, emerging fungi, and the rising scent of moist duff. A water-borne resurgence of desert life was in the making.
During the past few weeks, more rain has fallen, resulting in a cavalcade of change, a water-borne eruption of desert life. Flowers are blooming and creatures are stirring, many of which cannot be seen at other times of year. Giant millipedes are crossing roadways and threading their way through the woodlands, tarantulas are out of their burrows roaming the landscape, harvester ants are forming great clouds of alates bent on their one-day-per-year mating spree. Sonorous calls of amphibian passion are ringing through the night after every substantial rain. “Monsoon” as locals know it, is the one season that defines these lands and the ecology of southeastern Arizona more than any other. Arizona without its monsoon would be akin to Alaska without a winter.
One of many creatures that are revealed during this season is a small, nocturnal lizard with semi-translucent skin like gauzy velvet, big eyes with vertical pupils and movable eyelids, and the very rare ability (among lizards) to vocalize. Once encountered, the western banded gecko is not soon forgotten. More than once, I have heard the word “cute” applied to this beguiling little creature that rarely grows to more than four or five inches in length and remains hidden during daylight hours.
I discovered this little gem sheltering under an old piece of plywood. This banded gecko had lost its tail sometime in the past – the new one grew back lavender in color. A plump tail like this one indicates a good state of health, for the tail stores fats and water for the animal to draw upon during lean times, much like the tails of Gila monsters.
When predators chase after lizards, the first part of the lizard’s body that they make contact with is often the tail. In evolutionary response to this, many lizards have developed special abscission layers in their tails. Once contacted, the tail breaks off, leaving predators detracted by a wiggling morsel while the main course absconds to safety. Banded geckos have tails that break off with a very, very light touch; hence, I recommend against handling them.
When threatened or disturbed, banded geckos often curl their tails over their backs. Such posturing mimics the scorpions that they share habitat with, potentially scaring off some would-be predators. Banded geckos can also utter an audible squeak when frightened, making them one of the few lizards in the world capable of vocalizing.
During late July, the mass of tadpoles in our bird pond (see the previous blog post) transformed into toadlets in a matter of only ten days. The tiny young amphibians are now hopping their way into the surrounding woodland, disbursing at night when temperatures are cool.
This minuscule toadlet was photographed during its first day out of its natal pond, where it had spent the initial ten days of its life as a wriggling tadpole. At this stage of their lives, Couch’s spadefoot toads (Scaphiopus couchii), are tiny and vulnerable, fitting easily atop a mere dime.
On a warm early morning in mid-July, I took a walk and discovered an abundance of white-lined sphinx moths (Hyles lineata) almost everywhere I went. Most sphinx moths do their flying at night, but these moths were out in direct sunlight. They were specifically targeting wolfberry (Lycium spp.) bushes. The wolfberry was in flower, and the moths were hungry for nectar. With unerring accuracy augmented by rapid, graceful flight, they were moving from flower to flower, hovering at each one to insert their long tongues for sips of nectar.
A white-lined sphinx moth hovers over a wolfberry bush, deftly inserting its long tongue into the tiny white flowers to feed on nectar.
Note the bend in the moth’s tongue, a common trait among many species of sphinx and hawk moths.
White-lined sphinx moths have a very wide distribution that includes most of the United States. In some areas, their tongues are considerably shorter. Here, as they coevolved with certain types of nectar-rich flowers bearing long corolla tubes, their tongues adapted over time.
Since the first of this year’s summer rains on June 18th, we have received 4.25 inches of precipitation. Here is an image of our bosque taken just before the first rains.The same area, photographed yesterday. The difference is clear – the greening understory is composed primarily of pigweed (Amaranthus palmeri), a native plant that is of great value to a wide variety of birds and mammals. If the rains continue, this vivd understory will be capable of reaching heights of six to seven feet.This is what is left of a pigweed plant that grew after last summer’s monsoon rains. Pigweed retains much value to wildlife even after it has died and desiccated to a state like this one. Note that the plant has been recently fed upon, and that the cuts at the tips of each stem are sharply defined, cut cleanly at a steep angle. This is a signature left by the incisor teeth of a black-tailed jackrabbit. Nearly all rodents and lagomorphs (members of the rabbit order) leave such distinctive cut marks when they browse on similar types of vegetation. If deer or javelina had done this, the cuts would be rough with frayed edges and not cut at such steep angles.
Our area, the Middle San Pedro Valley, is served by a single dirt road that frequently endures serious damage after monsoon rain storms. I photographed this large wash near our home shortly after dawn, several hours after the flood had crested. The wet marks along either edge reveal a surging flow of flood waters that had crested at over 150 feet in breadth and four feet in depth. Flows this strong are quite capable of quickly carrying away almost any vehicle, even very large trucks.
The 2021 monsoon season in southeastern Arizona has certainly been one of the most memorable. At our home acreage in the Middle San Pedro Valley, 9.81 inches of rain have graced the land since the rains began on the second day of July. Other locations within less than 40 miles of us have received over 16 inches! The result is a landscape – and an ecosystem – burgeoning with a refulgence of renewed life. Since regional records have been kept, only the 1955 and 1964 monsoon seasons can compare. The scene above, featuring a landscape bursting with fresh, vivid green growth crowned by a rainbow is emblematic of Arizona’s monsoon.
As the monsoon wanes, migrant birds visit our feeders and watering places; notable appearances this year have included large numbers of Nashville warblers and an exceedingly rare blue bunting, a species that has never been “officially” recorded anywhere in Arizona. As the season approaches autumn, many changes occur in the world of reptiles and insects as well. Rattlesnakes are moving toward their hibernacula sites. The year’s last generation of butterflies brings flashes of beautiful color to the ecosystem. Other insects are reaching maturity, such as several types of native grasshoppers and katydids.
During the past two weeks, great numbers of mature lubber grasshoppers could be seen in many places in the valley floor. Their presence and abundance are a reflection of the monsoon rains that have enabled an explosion of plant life – a smorgasbord for grasshoppers. At this time of year, these bulky creatures have reached their final instar and are actively seeking mates.
A mature lubber grasshopper, Brachystolla magna. It is normal to see large numbers of these heavy, slow-moving insects during the tail end of our monsoon season. Note the tiny vestigial wings – this grasshopper is incapable of flight.
In mid-August, just after an afternoon rainstorm, I watched a female ornate box turtle emerge from the bosque to drink from a rivulet of rainwater. As she was slaking her thirst, I caught a flicker of movement some forty feet beyond her at the edge of the trees. It was a male box turtle. He had spotted her, and this was mating season. If you think turtles are slow, you have never seen an amorous male box turtle chasing a female! There is nothing subtle about box turtle sex. The males literally run down and attempt to corner the females, who move nearly as fast in their attempts to elude the charging males. Once the pair is joined, mating can take upwards of an hour.
A male ornate box turtle in hot pursuit of a prospective mate. I have seen this happen a number of times; what is most amazing to me are the distances at which the males first spot the females when the chase begins. In relatively level areas with open ground, males can visually discern females located at least 30-40 feet distant. Once a female is spotted, the male immediately makes a beeline to her at top speed.
The chase ends with a successful mating, allowing the circle of life to continue as it has for countless millennia.
Last week, my wife Kathleen discovered a new species of beetle, (one we had never seen here before), floating in a rain collection bucket. She rescued the hapless insect – a gorgeous, iridescent creature known as the Carolina tiger beetle.
This glittering, multi-colored tiger beetle got a new lease on life when it was rescued from a full water bucket.
Tiger beetles are incredible insects. The have been a part of my life since boyhood, when I often attempted to catch them as they raced across the ground with what seemed like otherworldly speed. Very few insects are faster on land than tiger beetles. Tiger beetles are hyper-alert predators equipped with unusually long hind legs for rapid propulsion. Their big heads house a pair of huge compound eyes capable of acute long-distance vision. The visual field of a tiger beetle encompasses more than a full hemisphere. When a prey item is spotted, tiger beetles run it down, then secure their meal with a set of long, formidable, serrated mandibles.
A lateral view of the Carolina tiger beetle, Megacephala carolina.
Most species of tiger beetles are diurnal, but the Carolina tiger beetle is an exception, preferring to be active after dark. I wonder if any part of these insects would glow under a UV light source? A number of other local nocturnal creatures glow under ultraviolet light, including scorpions and pocket gophers.
Butterflies are often abundant during the monsoon. As I was working outdoors one day, I noticed a fresh chrysalis hanging from some old wire fencing. I recognized its form; it had been made by a caterpillar that was a member of the butterfly subfamily Danainae. Insect species native to Arizona that belong to this group comprise three look-alike species: monarch, queen, and soldier butterflies.
The chrysalis hatched in a short time – only a week or so – to reveal a gorgeous queen butterfly. After hatching, the butterfly clings to the shell of its empty chrysalis, pumping blood into its unfolding wings.
Once the butterfly’s wings have expanded to full size, it is normal to see the insect remain perched for some time as it slowly opens and closes its wings, readying itself for its maiden flight.
Many plants native to the desert southwest have specially adapted themselves in a variety of ways to the summer monsoon season. One of the weirdest, most bizarre, and fascinating is a plant known as dodder. The first time that I encountered dodder, I stared in sheer wonder for some time while thinking “what the hell is that?”
Patches of dodder are a common sight during the latter half of the monsoon season.
Dodder grows as a vine, commonly forming a scattered profusion of very fine, yellowish tendrils that snake their way through the vegetation. It is a plant that cannot manufacture chlorophyll. Dodder survives by obtaining water and nutrients from other plants – it is an obligate parasite.
A closer look at dodder, (genus Cuscuta).
The weirdness begins just after a dodder seed sprouts following a monsoon rain storm. The minuscule seed – nearly microscopic – sends a small, shallow root into the soil while raising a tiny, thin tendril above ground. As the tendril grows, it starts to turn in upwardly-ascending spirals. It is not seeking light as most plants do – it is searchingfor a host. As the tendril lengthens, its spirals correspondingly enlarge, until it makes contact with a nearby plant. The tip of the tendril is chemosensory; it can literally sniff out what sort of plant it touches. Dodder is selective about the company it keeps – only certain plants will do as suitable hosts. If the tendril likes what it senses, it wraps itself tightly around the plant’s stem, then sinks a feeding tube – known as a haustoria – into the stem.
At this point, the seedling’s tiny root dies. The dodder plant then obtains all of its water and nutrients from its host. It will continue to grow and search, attaching itself to more plants. Once it has inserted enough feeding tubes into its victim(s), dodder reaches a point in its physiology that enables it to reproduce. Clusters of tiny white flowers erupt from the vine’s stem, ensuring the plant’s future.
Our local species of dodder sprouts clusters of small, white flowers – these grew from a dodder vine that had entwined itself on the stem of a pigweed (Amaranthus palmeri) plant.
So what is truly bizarre about this parasitic plant? Research has documented the fact that dodder actually steals sequences of DNAfrom its host plants’ genes, then incorporates them into its own DNA. The process is called “horizontal gene transfer.” This results in better survival for the dodder plants. It also enables them to manufacture strings of RNA that it sends back into the host plant, causing the host to weaken its defenses.
Dodder plants are classified as members of the Convolvulaceae – the morning glory family – with over 200 species worldwide. The genus, (Cuscuta), has a global range, occurring in tropical, subtropical, and temperate habitats. Dodder has a slew of common names, many of them derogatory – strangleweed, witch’s hair, devil’s guts, scaldweed, devil’s hair, and hellbine.
When considering this plant, we should strive to avoid the common propensity of our species to pass judgement on other life forms….often the result of our high capacity for arrogance-as-a-species combined with ecological ignorance. Simply because dodder is a parasite does not make it bad. Estimates place the percentage of parasitic organisms on Earth at 40-50% of all species. Clearly, parasitism is an essential part of the recipe for life on Earth. Here in the Middle San Pedro Valley, one of dodder’s favorite host plants is pigweed. Even when heavily infested with dodder, local pigweed plants continue to grow and produce viable seed.
July brought us over six inches of very welcome rain! The summer monsoon – one of five distinct seasons here – has returned to southern Arizona after a two-year near-absence. Purple martins are cruising above the treetops and a family of Mississippi kites has been visiting us for days. We are seeing rattlesnakes on a daily basis. On sultry, warm nights, elf owls have been calling in the wee hours of the morning. Saguaros are fattening as they transport water in their tissues. Native grasses are sprouting. The land and its life are rejoicing.
The changes on the landscape are incredible, happening with amazing rapidity and soaring fecundity. The mesquite bosque surrounding our home had been without a green understory during the entire past two years. Not any more! One glance out the window reveals a near-jungle of dense greenery standing five feet tall – much of it composed of one dominant plant with the unflattering common name of “pigweed.”
Fresh growth emerges with stunning speed and vigor after nitrogen-rich summer rains soak the land. This image is a week old; the understory plant community has doubled in height since then.
Pigweed is known to botanists as Amaranthus palmeri, and it is certainly not a “weed.” In the conventional sense, most of us consider weeds to be troublesome non-native plants. This one is a native species, and its presence speaks of great benefits to the land and its wildlife.
One of the primary winter forage plants for the deer that inhabit this river valley is pigweed. A good source of winter forage is critically important to wild ungulates. Rabbits, hares, javelina, and many rodents feed on the green plants in summer. Once the seed heads form, they tend to remain through autumn and winter on dead, standing plants. Great numbers of various species of sparrows winter in southern Arizona. The seeds of pigweed are heavily fed upon by many of these sparrows and other native birds as well. Something that is very obvious, but often overlooked by many people, is the fact that the dense stands of pigweed are shading the ground. I can’t stress enough how important shade is in desert ecosystems! The ground retains much more moisture and soil temperatures are far lower, allowing fungal hyphae and numerous other microflora and microfauna to work in shallower horizons of the soil. This benefits all life.
The summer rains bring many creatures out of hiding. Among these are toads, countless insects, red velvet mites, and the largest millipedes living in the United States…
Giant millipedes spend nearly all of their lives underground, typically emerging only after monsoon rainstorms. This one was about five inches in length; some sources claim this species can reach up to nine inches in length. These fascinating, innocuous arthropods can live for ten years, growing longer as they add more body segments every time they shed.I had taken several shots of the millipede, working close to the ground, before I noticed this small diamondback curled sixteen inches away. It never made a sound. When left undisturbed, these snakes are rarely aggressive. Their primary method of defense is stillness and excellent camouflage.When one of these huge beetles comes flying by, it is guaranteed to get your attention. This is a palo verde root borer, measuring in at three inches in length. These beetles are another example of the many species that are brought out from hiding by the rains.
For many of our of native amphibians, monsoon rains furnish their only chance to reproduce successfully. A strong population of spadefoot toads inhabits this valley, but they remain completely sequestered until strong summer rainstorms bring them up from their deep underground burrows. On July 3rd, the first monsoon storms rolled in – a succession of two storms with plenty of lightning and life-giving rainfall. That night, the landscape was ringing with the voices of hundreds upon hundreds of spadefoot toads.
Couch’s spadefoot toad is the most abundant amphibian in the Middle San Pedro Valley, but only summer residents witness them.A pair of Couch’s spadefoots mating. These amphibians must lay their eggs in water. In desert environments, the toads wait for summer storms to create suitable pools of water. Here, the male is grasping the female in a posture known as amplexus – when she lays her masses of eggs, he releases sperm into the water.
Spadefoot tadpoles mature more quickly than almost any other tadpoles on the planet – in as little as nine days. This is a species that has evolved to live in a hot, dry desert environment, where pools of water are not only rare, but tend to be very short-lived. It pays to mature quickly under such demanding conditions.It is hard to say what to call the amphibians in this brief period of their lives; tadpoles or toadlets? At this stage in their development, the tails shorten very quickly. As newly formed toads appear, they can be seen hopping by the dozens out of their natal pond. Just two days ago, despite the fact that I am always on the lookout for rattlesnakes, I nearly stepped on this one that was well camouflaged under the ramada. I am glad that we did not have an unfortunate interaction.
