Categories

A Female Arabesque Orb Weaver in Lufkin, Texas

— BugsInTheNews is a VIEWER-PARTICIPANT WEBSITE. This article by Jerry Cates and Julia E., first published on 9 April 2010, was last revised on 1 December 2012. © Bugsinthenews Vol. 11:04(07).

——————————

Arabesque Orbweaver (Neoscona arabesca); Julia E., Lufkin, Texas 1108 Right Dorsolateroposterior

Arabesque Orb weaver


Julia wrote:

Jerry,

After reading your information on my jumping spider, I couldn’t resist digging through my pictures of another specimen. You might say this is the one that opened my eyes to a spider’s beauty.

“?”

It is definitely true that beauty is in the eye of the beholder. Most of my friends don’t think spiders are at all beautiful!

In November 2009, this particular spider was found at the same location as my jumping spider–around a pond but more out in the open. She had a large web built near a woody path and because of her size she was easy to view.

I thought, at the time, that I had gotten carried away, taking so many photos. But, now, after seeing what you can learn from just one photo, I can’t resist the urge to find out what you’ll be able to see in several. I’m not in a big hurry, so please don’t rush to respond. I just wanted to share what I found and learn a little more about what I’m photographing.

Thanks in advance,

Julia

It isn’t hard to get carried away by arachnophilia (love of spiders, the opposite of arachnophobia). Ask Pierre Paquin and Nadine Dupérré, two professional arachnologists who, in 1999, got swept off their feet by a spider class they took in North Carolina to supplement their studies in biology.  Since then both have made major contributions to the field of arachnology. Perhaps Julia is poised to become a world-renowned arachnologist, too… or, more likely, like me she will remain at her “day job” and — outside of academia — apply her appreciation for these animals by watching, reading, and writing about them.

Needless to say, I was very pleased to receive Julia’s photos of this spider. They are all excellent, in good focus, and posed almost professionally. That last point, about almost professional poses, bears a little explaining. Professional poses are too plastic. Julia’s are not like that. They have a breathlessness, an air of anticipation, with each of them, that can only come from unposed, but genuine, beauty.  Like one of the beautiful illustrations that Nadine Dupérré is so famous for drawing, unposed, but complete, and inspiring.

Arabesque Orbweaver (Neoscona arabesca); Julia E., Lufkin, Texas 1108 Dorsal abdomen, from retreat

In Retreat

Well, Julia is right about beauty and the beholder’s eye. It is possible you see nothing beautiful in the photos displayed here thus far, but I suspect that will change. As you walk through these photographs with me, you will be treated to  a fascinating glimpse into the life of a female orb weaver. If you have any imagination at all, you will–in your mind’s eye, at least– even begin to dance with her.

In this series of images, each of which captures just a tiny portion of her late-afternoon schedule, you will learn from her how she goes about the work that starts each day, weaving–actually re-weaving–her web.

All day long, she’d been curled up in her retreat, “hidden” from view.  Of course, if you knew where to look, as Julia did (see the photo at left), you’d find her there, looking oh, so pitiful.

Most predators who find nocturnally active spiders hidden in their diurnal retreats pass them over for more active, daytime animals that are scampering about looking very much alive. They see her pitiful, curled up form, and assume she is either sick or lifeless. That’s what she’s counting on, for she maintains this forlorn, crumpled appearance until the sun gets low on the horizon and nightfall commences and the sky grows dark.

Ah! but when that time arrives, she comes alive. And alive she needs to be, because the huge web she built at dusk the day before is no more. She painstakingly took it apart, piece by piece, the previous morning, as the dawning sun crept toward the horizon and darkness fled the sky.

Arabesque Orbweaver (Neoscona arabesca); Julia E., Lufkin, Texas 1108 Frontal body

Frontal Body

By the time Old Sol finally peeped over the trees and lit things up with his warming rays, her web was entirely gone. Recycled, as a matter of fact.

You might have thought  that humans invented that, but no… this miniscule orb weaver comes from a long line of recyclers whose forebears spun webs, all over the earth, millions of years before humans existed.

But she didn’t put her web in a plastic bucket at the curb.

She ate it.

Her web is made of complex protein molecules, all entirely edible. These molecules are broken down inside her body, so they can be used again, building them into the next web she spins.

How economical she is… So, yes, we didn’t invent economics, either.

To be fair, though, economy is not her only object.

By dismantling her web each morning, she succeeds in obliterating the largest, most visible sign of her presence in that area. Some organisms — including birds, predatory insects, predatory spiders, lizards, and geckos — eagerly search out spider webs, hoping to find a juicy spider to eat. But they don’t get any help from her.

Arabesque Orbweaver (Neoscona arabesca); Julia E., Lufkin, Texas 1108 Right Dorsolaterofrontal

Front and Side

And let us not fail to point out that she has even more practical reasons for recreating her web each day. Although the tiny silk threads that hold it together are truly stronger than steel wires of the same diameter, when an insect alights upon those threads, some of the ones the insect comes into contact with will break under the weight of the landing. This effect is intentional, as with that breakage the insect loses its footing and bumps into more and more of the surrounding threads, some of which are sticky enough to entangle it in the  netting. The entrapped insect then struggles against its bonds, which only fixes the threads more securely. Later, in the ensuing struggle with the hungry spider, even more of the threads are broken. As a result, every time a morsel of food drops into the web, damage to its structure of one degree or another is produced.

So, what begins the night as a thing of beauty and delight meets the first rays of dawn of the next day as a bedraggled rag, torn asunder by a series of nocturnal food fights. The arachnid mistress of the web could try to repair it, and some spiders (for example, orb weavers in the genus Nephila) do just that, over and over again. But not Neoscona arabesca. She chooses, instead, to reconstruct it — according to her exacting standards — every night. It takes her less than half an hour, most of the time. Sometimes, when winds are high, it may take as much as an hour. If it rains at dusk, she may have to rebuild it several times, over a period of hours.

Willis John Gertsch (b.1906-d.1998), wrote the following in his 1979 book American Spiders (p. 2):

The orb web has long been a symbol of the spider in the mind of man, who sees in its shimmering lightness and intricate, symmetrical design a thing of wonder and beauty. Such esteem is well merited, because the orb web is the most highly evolved of all the space webs developed by the sedentary spiders. It represents a triumph in engineering worthy of great mechanical ingenuity and learning; yet it was arrived at by lowly spiders, which even by their most argent supporters are credited with hardly a gleam of what is called intelligence.” True. Intelligence would imply an ability to improvise in ways these spiders cannot. They build their webs according to a set of instinctive commands, programmed into their brains. Still, the ability to create such webs demands–if nothing else–respect.

Arabesque Orbweaver (Neoscona arabesca); Julia E., Lufkin, Texas 1108 Dorsofrontolateral view

Front and dorsum

This may be a good place to point out that this specimen is a female. We know that intimate fact merely by taking note of the spider’s distinctive sexually dimorphic features. For example, we can tell this is a female by the rather obvious shape of the pedipalps that are projecting forward of the face, from each side of the anterior head.

If you click on the image at left (or any other image on this website, generally speaking) it will be replaced by a larger version that can be examined more closely.  On that enlarged image you will notice that the pedipalps (abbreviated as palps) have no obvious shape that distinguishes them from the spider’s legs. They are structurally different, though, and if you count the segments, you’ll discover that they have one less than the legs. The next to last segment in each leg, the metatarsus, is lacking in the palps.

I confess, then, that the expression ”rather obvious shape” is slightly misleading. Were our specimen a male, the pedipalps would have a truly obvious shape that differs from that of the legs. The pedipalp’s terminal segment, the tarsus, is swollen (and often rather ornate in its architecture besides) in the male, but–as with Julia’s specimen–is shaped normally in the opposite sex. From the perspective of an arachnologist, this lack of a swelling on the terminus of the palp is rather obvious, and–at least for this family of spiders–portends of femininity in a mighty way.

Arabesque Orbweaver (Neoscona arabesca); Julia E., Lufkin, Texas 1108 Ventroposterior

Underneath

Other features distinguish the sexes in the orb weavers, too.

One of the most common examples of sexual dimorphism (defined as the systematic differences in form between the sexes within a species) in the orb weavers is body size. Males are almost always much smaller.

In the genus Neoscona that still holds true, but the difference is size is not as extraordinary as in some of the other genre. The male of the yellow garden spider (a member of the genus Argiope), for example, is typically only one 50th the size of the female.

By comparison, a male Arabesque orb weaver has a body one-third to two-thirds the length of that of the female.

The male is also shaped somewhat differently, particularly in the way the prosoma (the anterior, or forward half, of the body) compares in size to the opisthosoma (the posterior half of the body). Males have prosomas that are about the same size as, or slightly larger than, their opisthosomas. Further, the opisthosoma of the female, holding as it does the ovaries and eggs, tends to be globular in shape, while that of the male, whose internal reproductive organs are much more modest and compact, is elongated, along the long axis of the body.

Arabesque Orbweaver (Neoscona arabesca); Julia E., Lufkin, Texas 1108 Ventral body

Underneath

The genus Neoscona is a member of the Araneidae family of Araneomorph spiders. We know this spider is in the infraorder Araneomorphae, because it has diaxial–opposed–fangs. That is, they open and close like scissors, not (as in the Mygalomorphae) paraxial–parallel–like the tines of a rake. Most of the spiders we find in the wild, and all of the orbweavers, are Araneomorphs. Tarantulas, and trapdoor spiders, on the other hand, are mygalomorphs.

We also know that this araneomorph is a member of the Araneidae family. And though we might have gotten that information by following a dichotomous key (using, for example, the key in the book Spiders of North America, by Ubick et al., 2005, which would be a most scientific method), we could also arrive at the same conclusion by way of extrapolation, using our knowledge that she is one of the spiders that build common, orb-shaped webs.

The Araneidae are the common orb weavers. A few other families are also orb weavers, but with caveats. For example, spiders in the Tetragnathidae family are known as long-jawed orb weavers; their chelicerae (jaws) are unusually large in comparison with the head, hence the name, but that caveat applies most specifically to the males. Many tetragnathid females have quite normal chelicerae. So, we sorta punted on that one, but it was a good punt…

You may be curious to know how, and why, I deigned to identify this specimen as an arabesque orb weaver. That’s an excellent question, especially considering that most keys to the genre of the Araneidae (see, for example, Herbert Levi’s 2002 key to American araneids) begin with references to the arrangement of the spider’s eyes. It happens that, although Julia’s photographs are dazzling, they do not provide a good view of the eyes. “Why” is something of a minor mystery, but my guess is that hairs on this spider’s particularly hirsute anterior head obscure the eyes so thoroughly that they just don’t show up well. Some specimens are like that. So, what to do?

Arabesque Orbweaver (Neoscona arabesca); Julia E., Lufkin, Texas 1108 Right Dorsolateral

Side View

Well, we simply have to look for things that can be seen, and make do with them. In this specimen we have plenty of very clear features, especially on the dorsal and ventral abdomen, that tell us a lot. Prior knowledge is often better than a key, if it is coupled with a broad range of experience. I would prefer taking you through a key, step by step, but when that isn’t possible we are forced to take liberties based on what we’ve observed in the past.

For example, the dorsal abdomen of this specimen has a kind of paisley pattern on its anterior third, which experience tells us is characteristic of several species of orb weavers in the genus Neoscona.

And the middle and posterior thirds of the dorsal abdomen have a series of short, dark marks, lined up on each side, that are pointed toward the sides, and then are hooked toward the front.

The arabesque orb weaver has those marks, but so do several other spiders, so we need to look for additional  features to hang her identity on with greater certainty. And though many professional arachnologists tend to downplay their importance, it has been my experience that–at least among the Araneidae–the grossly visible marks displayed on the ventral abdomen tell us a lot about the identity of many, if not most, orb weavers. Often, in fact, just glancing at those marks can immediately inform us on the genus.

Arabesque Orbweaver (Neoscona arabesca); Julia E., Lufkin, TX 11.08--Ventral Abdomen

Ventral Abdomen, annotated

The annotations of the image at left can be read more easily by clicking on the image to bring up its enlarged version. Let’s first notice the basic features common to most orb weavers:

Note the book lungs, covered by a reddish sclerotized (thickened and hardened) tissue that trends to yellow toward the middle of the abdomen. The second book lung is located on the other side of the abdomen, but is partly obscured by the coxa of Leg IV.

Between these lungs is a darker tissue that, at its lower end, borders the spider’s epigynum. This is the sclerotized portion of the female’s external genitalia, and includes–for entelegyne spiders (which have hardened external genitalia, as opposed to haplogyne spiders, which lack these external structures)–an atrium and a scape.

The atrium is the cavity below the scape, and typically is not discernible except under relatively high magnification. The structure of the scape, by comparison, is often somewhat easier to discern. But, as we do so, we begin to dabble in the esoteric side of the work.

Julia’s spider has a scape that appears smooth, rounded, and uncomplicated in form, sort of like the cockpit and nose of a stealth fighter jet. This structure is consistent with the scapes typical of the genus Neoscona.

That done, we now proceed to examine the complex markings in the center of the ventral abdomen. This complex is very distinctive for most species of orb weavers, and variations within the complex are unique to certain species.

The center of this complex, for Julia’s specimen, is dark, and shaped like a thick-stemmed chalice, of the kind King Arthur might have had on his Round Table. On each side of the stem is a bright, pale-colored blotch. Below each of these blotches is a smaller, yellowish blotch.

Whenever I see this complex of markings on the ventral abdomen of an orbweaver, I usually feel quite comfortable identifying the specimen as an arabesque orb weaver. Other ventral marking complexes, displayed by other species of orb weavers, are similar to this, but not identical to it.

—————————————–

Taxonomy:
  • Kingdom Animalia (ahn-uh-MAYHL-yuh) — first described in 1758 by the Swedish taxonomist Carolus Linnaeus [23 May 1707 – 10 January 1778], using the Latin word animal = “a living being,” from the Latin word anima = “vital breath”, to refer to multicellular, eukaryotic organisms whose body plans become fixed during development, some of which undergo additional processes of metamorphosis later in their lives; most of which are motile, and thus exhibit spontaneous and independent movements; and all of whom are heterotrophs that feed by ingesting other organisms or their products; 
  • Phylum Arthropoda (ahr-THROPP-uh-duh) first described in 1829 by the French zoologist Pierre André Latreille [November 20, 1762 – February 6, 1833], using the two Greek roots αρθρον (AR-thron) = jointed + ποδ (pawd) = foot, in an obvious reference toanimals with jointed feet, but in the more narrow context of the invertebrates, which have segmented bodies as well as jointed appendages;
  • Subphylum Chelicerata (Kehl-iss-uh-RAH-tah) — first described in 1901 by the German zoologist Richard Heymons [1867 - 1943] using the Greek noun χηλη (KEY-lee) = a claw, talon, or hoof + the Greek noun κερας (Ser-as) = an animal’s horn + the Latin suffix ata — which by convention is suffixed to the names of animal subdivisions — to refer to animals that have specialized appendages before the mouth that they use in feeding, capturing and securing prey and that — in the case of spiders — are further equipped to inject venom and digestive agents into their prey; 
  • Class Arachnida (uh-RAKH-nuh-duh) first described in 1812 by the French naturalist and zoologist Jean Léopold Nicolas Frédéric Cuvier [August 23, 1769 – May 13, 1832], usually referred to as Georges Cuvier, using the Greek noun αραχης (uh-RAH-kes) = a spider, in reference to all eight-legged arthropods, including such disparate animals as ticks, mites, scorpions, harvestmen, solpugids, and spiders; 
  • Order Araneae (uh-RAY-neh-ee) — first described in 1757 by the Swedish entomologist and arachnologist Carl Alexander Clerck [1709 – 22 July 1765], who used the Latin word aranea = a spider or a spider’s web, to refer to eight legged arthropods that spin webs.; 
  • Family Araneidae (Air-uh-NYE-dee) — first described in 1864 by the French arachnologist Eugene Simon (30 April 1848 – 17 November 1924) using the Greek words εριον (Air-ee-on) = wool to refer to a family of spiders that produced woolly webs;
  • Genus Neoscona (nee-oh-SKOH-nuh) — first described in 1864 by the French arachnologist Eugene Simon (30 April 1848 – 17 November 1924) using the Greek words νεω (NEE-oh) = spin + σχοινος (SKOY-nos) = well, dear reader, that’s an interesting question. Here’s the deal: Master Simon was, at the time he penned this name, a mere lad of 16. It is said that his grasp of Greek was never much to brag about, but at 16 it was abysmal. In any case, he wrote that what he meant by the Greek word σχοινος was, in English, the word “reed,” which he chose in order to make reference to the fact that he had found certain of the spiders of this genus spinning their webs among the reeds near the water. Attempts made a few years later, by others more versed in Greek, to modify Simon’s construction in order to bring it into etymological consonance failed to stick, thankfully due to the rule of priority. The first to pen the name gets to live with that name, whether it makes perfect sense or not, which is as it should be…
  • Species Neoscona arabesca (ahr-ubb-ESS-kah) — the specific name arabesca was first described in 1841 by the French naturalist Charles Athanase Walckenaer (1771-1852), who appears to have mixed the Greek word αραβος (AHR-uh-bose) = a rattling, gnashing of teeth, with the Latin word esca = victuals, to reference the frenetic manner in which these spiders attack and consume their prey. Unless privy to this etymology, most typically pronounce the specific name air-ubb-ESS-kah, thinking it relates in some way to Arabia, which — from all indications — it does not.

—————————————–

References (for a list of all of Jerry’s references to scientific literature, click here):

—————————————–

— BugsInTheNews is a VIEWER-PARTICIPANT WEBSITE.Questions? Corrections? Comments? BUG ME RIGHT NOW! Telephone  Jerry directly at 512-331-1111, or e-mailjerry.cates@bugsinthenews.info. You may also register, log in, and leave a detailed comment in the space provided below.

Leave a Reply

  

  

  

You can use these HTML tags

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>