The Coleopteran Gold Rush (…and a chameleon of a beetle)

It was a sunny day in late October, and so I decided to take a brief drive over to the bridge that overlooks the west fork of the Trinity River for my lunch break to see if any interesting invertebrates were hanging out along the public right-of-way in the tree line that skirts the edge of a large tract of bottomland cross timbers forest that is owned by the city dump.  I know, this sounds like a terrible place to try to get away and enjoy nature, even briefly, but in all actuality it is not as bad as it sounds.  I have never seen the gate to the entrance to the place unlocked, let alone open.  Shut out the picture in your mind of some obsessive bug nerd peering into the low bushes with a stinking mountain of refuse in the background, blocking out the sun.  This is just an overgrown meadow lined by stands of sugarberry, bumelia, and honey locust conjoined by inseparable tangles of greenbrier, ampelopsis, and wild grape.  Above them stand their rightful elders: red oak, blackjack, ash, pecan, and willow.  A single patriarchal ancient cottonwood stands in the midst of this line of these mixed ranks of native hardwoods, its skeletal branches, devoid of leaves for several years now, still reaching up to the sun that no longer provides the dried, fibrous trunk with sustenance.  Red bellied woodpeckers and blue jays dart among the canopy above.  Occasionally a majestic blue heron wings by overhead en route to the nearby riverbank for an anticipated leopard frog lunch, its call a deep, guttural chortle on the autumn wind.  Gray treefrogs cling to the lowest branches of the trees as if they had been glued there.  They are so abundant I almost never fail to see one whenever I visit.  Great spotted purple butterflies compete with phaon crescents, eastern tiger swallowtails, and a host of other native butterflies among the low-growing lantana around the T-posts of the fence.  No, the west fork fringe of roadside around the “dump grounds” is actually not such a bad place to be.

The main reason I had been coming here for going on several weeks now had been to beat the lowermost branches of the trees for an exquisite member of the family of jewel beetles known as Buprestidae.  And in spite of all the good real estate (Buprestids as a general rule are fond of dead and – especially – stressed and dying trees) the species I had in mind was found in a slightly different microenvironment: the lowly sugarberry tree.

The sugarberry tree is a great thing, especially when you happen to be a buprestid beetle of the genus Agrilus and of the species macer.  At around ½ inch in length, with an oddly narrow, deeply crevassed elytra that appears to be spray painted gold in the sunlight, one would think they would be relatively easy to spot, but one would be wrong.  When sitting motionless in the dappled shade that filters in between the compound leaves and thin, drooping branches of the sugarberry tree in the bright noon sunshine, Agrilus macer blends in superbly and surprisingly well, so much so that they are practically invisible unless one happens to move.

CK-Agrilus macer

Agrilus macer

With beating stick/butterfly net and a white sheet stretched taut across an “X” shaped wooden frame, I set out across the tree line, my heart set on adding what would only be my fourth specimen of this unique species to my insect collection.

I found a tree fairly quickly, its unmistakable chaotic corking limb formation seeming to sprout from its short, twisted trunk from all angles, like a crop of wild hair.  Sugarberry trees are in the family of elm trees Ulmaceae, a huge genus that also includes such common natives as the slippery elm and American elm.  Aesthetically they are not too appealing, at least not compared to some of their more park-popular kin, but to a hungry macer they are the center of the universe, the wellspring of life, where the beetle’s entire life cycle is played out on and in the branches and trunks of the tree.

I placed the beating sheet (as they are collectively called among us bug brains) beneath the tree and gave the outermost branches a few sharp raps.  The goal of this endeavor (which I am certain appears to highway passersby as odd behavior) is to dislodge any invertebrates which may be residing there.  Although it sounds kind of droll, to a beetle or spider or caterpillar enthusiast (of which I am all of the above), it is like playing Mother Nature’s slot machine, and many previously undescribed species have been discovered in this manner, whereas they would otherwise have most likely gone unnoticed.

The slot machines are particularly loose between early June and late August, when most of our buprestid species are in the midst of their emergence and subsequent breeding season.  So yeah, it was a bit late in the year to have expectations set so high as to find one, but the weather sure was more desirable this time of year, as mid-June at high noon on the river floodplain can be one miserable place to be, beetles or no beetles.

The sugarberry produced no macer, although it did produce an emerald green nymph of the predatory pale green assassin bug.  A stand of willows grew at the base of a large, gnarled elder of the same kind.  The flaky, shingled bark is considered a delicacy to the handsomely marked willow long horn beetle, so I thought, “Why not? It’s not Agrilus macer, but it’s worth a shot.”

The first whack of the branch displaced a half-dozen shield bugs, flat, dime-sized pale yellow-green insects with constantly twitching antennae.  While shield bugs as a whole are among the most common of finds on the beating sheet, I had never encountered this particular species before, and so I collected a small series of specimens to study (and hopefully identify) back at home.  The next few strikes to the branches produced more and even more of them.  Their abundance here is a testament to their extraordinary camouflage, as I was unable to visually pick out so much as a single bug on the tree with my naked eye.

Another interesting willow connoisseur that ended up on the sheet in the aftermath of my assault was a stout, blue-green caterpillar around two inches in length, its body bespeckled with a generous sprinkling of raised pale flecks, as if it had been lightly dusted by a can of white spray paint.  The head had a strangely slanted, angled appearance, and the creature’s posterior end bore a curved, wicked-looking (though harmless) sickle of a horn.  This was the larvae of the twin-spotted sphinx moth, a pretty species with underwing eyespots of blue inside pink.  Although a few adults had turned up at my black light earlier in the summer, this was the first caterpillar I had found of the species.  These belong to the family of moths known as Sphingids, or hawk moths, so named for their body shape, when, with wings at rest, somewhat resembles the form of a diving raptor.  While the majority of hawk moth larvae are specialist feeders on vines in the grape family, a significant number of species feed on various hardwoods.  Like Agrilus macer, each species is usually fairly host-specific, and the twin-spotted is no different, feeding mostly on trees in the willow family.

I almost didn’t see it.  In fact, I didn’t at first, but as I knelt down in front of the sheet for closer inspection, there sat something remarkable, looking so out of place among the greens and browns of dislodged foliage that it didn’t even appear real.  Between two long, thin willow leaves sat a tiny beetle, barely 1/8 of an inch in length, that looked as if it had been dipped in solid gold.

CK-golden tortoise1

The golden tortoise beetle

I knew its identity the moment I laid eyes on it: it was a golden tortoise beetle, Charidotella sexpunctata, a species that had been immortalized in one of my favorite childhood field guides.  The specimens in the plate photograph had been taken in Arizona, and the range had simply read “Arizona.”  So I had made absolutely no effort to find this species in the field.  And yet here it was, amidst the torn greenery of a common sand willow in the company of sphinx caterpillars and scuttling shield bugs along the banks of the Trinity.  Talk about a range extension!  (I learned after some research that the beetle’s actual range is much broader, and that it is well documented in Texas.)

I fumbled in my pocket for a vial, and as I gently scooped the creature inside I noticed another beetle of identical shape and form as the first, except this one was colored orange with black spots, much like a ladybug.  Into the vial it went as well, along with a sprig of willow to make them feel a bit more at home.

By this time I figured I had better get back to work (the kind of work that actually pays my bills) and so I slipped the vial containing the two tortoise beetles into my pocket and headed for the truck.

Later that afternoon I picked my son up from school, and as soon as he climbed in I handed him the vial.  “Check out these tortoise beetles I found at the river today,” I exclaimed.  “One of them looks like it has been painted gold.”

Zee held the vial aloft, squinted, and then flipped open the lid for a closer examination.  “This bug isn’t gold-colored, but it is pretty,” he commented.  “Metallic purple!”

“What?!” I cried, “you’re crazy, kid! Let me see that!”

Sure enough, one of the beetles still looked like a flat ladybug, but the other was now exactly as my son had described it: a shimmering, shining light purple.

“It changed colors!” I said with a shout.  I imagine I felt not unlike the first Native American that had laid eyes on the green-to-brown pigment shift of a green anole.

Later that evening, my wife balked at the mention of this newfound phenomenon.  “Sure,” she said.  “Color changing beetles…far out, man!”

“I can prove it!” I retorted, and went for the vial.  Again I was in for a surprise.  The gold specimen turned purple specimen had gone through yet another color change!  This time its elytra appeared a soft baby blue.

At the moment I thought I had stumbled onto some incredible scientific discovery previously unbeknownst to the world of insects, but of course a little research into the natural history of this species (this time from a much more reliable field guide) explained how the golden tortoise beetle changes colors for a number of reasons, including its developmental stages, while breeding, and especially in response to foreign stimuli, where the beetle feels stressed or threatened.  This is apparently accomplished through the hydration and dehydration of the elytra, which is layered with a series of tiers of varying thickness.  These layers themselves are composed of even smaller, groove-like layers.  Each tier reflects a different color of light.  The three together produce gold, but when drained of fluid the bottom-most layer (a dull reddish-brown) fills the otherwise transparent wing covers.  The grooves also smooth when hydrated, giving the insect a shiny, metallic appearance.  Deprived of fluid, the shine quickly fades, giving the beetle a comparatively lackluster appearance.  So far this species and a single South American species of tortoise beetle are the only organisms known to science that change colors in this manner.CK-golden tortoise2

While I had failed to find the coveted Agrilus macer, I had come away with a beetle even more golden and (at least in my experience) less commonly seen.  While I hadn’t exactly made any new earth-shattering discovery in the world of entomology, I had experienced a fascinating aspect of the natural history of one of our state’s most beautiful and overlooked species first-hand.

On a side note, being the ever-obsessive beetle head that I am, I returned the next day to this same location to see if I could turn up any additional specimens of golden tortoise beetle.  I didn’t find any, but in a moment of irony I took a whack at a scrubby looking little sugarberry on the way out and to the sheet fell a splendid little gold-dusted buprestid, Agrilus macer!

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