An Inferno of a Summer, Huge Arthropods, and Arizona’s Tiniest Mammals

This has been one of the driest and hottest summers I can recall here in the Middle San Pedro River Valley. During “normal” summers, monsoon rains arrive between the middle and the end of June and continue through August and much of September. The two previous monsoon seasons brought us a welcome abundance of rain, but this year has remained very, very dry. Daytime highs for the past six weeks have averaged around 106°F., with more than a few days reaching 110° or higher. This year’s highest temperature registered at a crispy 115°F. on July 17.

Our mesquite bosque remains dry, the understory of dense London rocket plants yellowed and brittle. Usually, by the end of July, this scene should be bursting with vivid green growth in the form of Amaranthus palmeri and many other native plant species.

Despite our xeric summer, velvet mesquite trees in our bosque have produced a nice crop of pods, followed by a second flowering during the past couple of weeks. The trees are drawing on water from last summer’s abundant storms; mesquite has the rare ability to transport water in both directions within its extensive, very deep root system. Water can be transported deep underground and stored for later use.
A fresh splay of velvet mesquite blossoms perfumes the air and reminds us that desert plants have evolved uncanny mechanisms to stay alive and even thrive under dry, difficult conditions.

Mesquite blossoms lead to garlands of bright green pods growing from pendant branches. Mule and whitetailed deer love to feed on low-hanging bunches of these young pods. When ripe, the seed pods turn yellow and fall to the ground. There, they become one of the most crucial and nutritious wildlife foods in the entire ecosystem, eagerly fed upon by a very long list of native animals from mice to coyotes to bears and many more.

Despite the drought, this was a banner year for a widespread local species known as catclaw acacia, Acacia gregii. (See the photos in my previous blog post.) Throughout the valley, these large shrubs/small trees flowered explosively. The scent from their blossoms is intoxicatingly wonderful. Much like mesquite pods, the seed pods of acacias are fed upon by a wide variety of native wildlife.

Dry conditions leave fine coatings of dust on our driveway – an excellent newspaper that I strive to read daily. This summer has revealed tracks of mice, kangaroo rats, gray foxes, coyotes, raccoons, mule and whitetailed deer, a cougar, hooded skunks, quail, doves, and other birds including this trackway of a Chihuahuan raven.

A closer look at the raven’s tracks reveals their relatively large size, distinctively lobed feet, and shallow drag marks made by their posterior claws.

A mystery…last week, I noticed something I had not seen before: dense clumps of small, black native bees forming in certain graythorn (Zizyphus) bushes. I have no idea what is going on here, nor what species these bees are – there are well over 1,200 species of native bees in this ecosystem, representing the richest known bee fauna in the world.
I found this adult giant mesquite bug (Thasus californicus) roaming under my ramada the day before I posted this blog. These are large insects that are true bugs (Hemipterans) as opposed to a type of beetle (Coleopterans).

A lateral view of the mesquite bug reveals the tube-like mouthpart that it uses to feed on plant liquids. The tube is inserted, syringe-like, into the stems of plants. These specialized feeding tubes are a primary characteristic that separates true bugs from beetles.

Prior to maturation, giant mesquite bugs exist in the form of wingless nymphs. The nymphs form colonies that feed on liquids from various species of trees and shrubs. The nymphs go through several instars before finally transforming into adults, all of which exhibit these very bright red colors. The nymphs are protected with self-manufactured noxious chemicals that make them taste bad to predators, hence their aposematic coloration.

Arizona’s smallest mammals are shrews; I found this one – dead but still warm – on the floor of our bosque. This species is known as the desert shrew, Notiosorex crawfordi. Shrews are among the most highly energized, frenetic mammals on Earth. They require remarkable amounts of food – up to nearly half their body weight on a daily basis. They almost never stop moving, constantly on the hunt. I wonder how they have time to dream.

This sight greeted me a few mornings ago, when I walked outside just after dawn to see this giant centipede (Scolopendra heros) clinging to the wall of my adobe building. The broom handle gives a sense of scale. This one was just under seven inches long – and they get bigger than this, up to nine inches in length. Very large specimens measure around an inch in width across their backs, are equipped with formidable pincers, and can move at astounding speeds.

High winds snapped this velvet mesquite trunk at the location of a cavity hollowed out by Gila woodpeckers. I have seen such tree breaks many times, both locally in this southern desert and in the northern Rockies. There is a complex relationship between cavity-making birds and their varied roles in forest ecology that may be more important we know.

A close look at the exposed woodpecker cavity shows the remnants of a successful nesting season. Last month, a pair of ash-throated flycatchers raised a batch of young within the sheltered confines of this tree cavity.

This image should be entitled “HOPE”… a series of empty, dry water buckets under my roofline, hoping and waiting for the summer rains. Why collect rainwater when we have a well, particularly summer rain water? The summer storms often feature stunning amounts of lightning, which allows substantial amounts of elemental nitrogen to be carried from the atmosphere (via rainfall) down to the ground, where it greens the Earth. All gardeners should learn that summer rain water collected after lightning storms works magic on plant growth.

8 thoughts on “An Inferno of a Summer, Huge Arthropods, and Arizona’s Tiniest Mammals”

  1. Loved this informative and passionate post. Thanks for sharing your desert with is in this way.

  2. Good morning, Ralph, wonderful to get your blog as always. Love the coloration on the mesquite bugs. , The remnants of the ash-throated’s nest look like cholla spines but are grass stems, I think. Our ash- throated’s usually arrive by April 1st and are gone by August 1st. A few days ago there was a family in the cottonwood, flying about and calling to each other; such joy! I heard a call from the last one yesterday, probably on its way south today; my favorite bird of summer. It’s been hot and dry here too, not much in the way of insects and the orb weavers are having a hard time of it. Earlier in the spring there were carpets of verbena hiding under the long dry stems of last summer’s gramma grass.

    1. Luisa,
      It is nice to hear from you again. I hope your summer is going well.
      You were right about the nest contents; the nest was constructed mostly of
      bristle grass, genus Setaria. That surprised me, because that grass is very
      bristly and clings to clothing like velcro. Apparently, it works to raise a
      brood of ash-throated flycatchers! Let’s hope we get some rain soon.

  3. Hi Ralph,
    I am no expert but I wonder if those native bees are swarming? I keep honeybees and swarming is their way of reproducing the hive. I believe native bees swarm, too, but seems late in the season to be doing this. Maybe a hive wasn’t queen right? Maybe it is a defensive swarm? I don’t know a thing about native bees but it’s a guess from the pic.

    1. Hi Kate,

      I’m happy to know that you are still reading my blog. Your comments about swarming
      bees are interesting – I’d love to know if there are native bees that engage in that
      sort of behavior. I have witnessed many large swarms of (non-native) honeybees here.
      When a huge, rolling black cloud of thousands of bees appears, it can be frightening.
      The swarms are incredibly loud, and all of the “wild” honeybees in southern Arizona
      are the infamous “killer bee” genotype. They have killed people here, and even fully
      grown horses.

  4. I was trimming a Zizyphus today, I love Graythorns they provide berries for wildlife. Enjoyed your blog, leaned a lot,

    Thank You Again Ralph,

    Gilbert

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