Territorial, Subsocial Spiders in Marble Falls, Texas

This article by Jerry Cates was first published on 1 December 2014, and last revised on 23 December 2014. © Bugsinthenews Vol. 15:12(01):

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Abstract: The author reports on a group of spiders recently observed in Marble Falls, Texas. They were found at a commercial structure, inhabiting a communal web attached to the ceiling of an exterior vestibule. Individual spiders were regularly spaced within that web, ensconced in inverted, cup-shaped retreats. The silken lines composing the communal web were nearly invisible to the naked eye, giving the impression the embedded retreats were floating in air. Each retreat was separated from the others, across the ceiling’s horizontal plane, such that each spider appeared to control a private prey-capture zone. This implied that, although the group of spiders evidently cooperated in building and maintaining the communal web, prey capture and consumption was solitary work. Microscopic analysis of a female specimen collected from this group on 11-29-2014 indicates these are araneids, in the genus Metepeira, and most likely Metepeira labyrinthia (Hentz) or Metepeira comanche (Levi, 1977).

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Fig. 001. Communal web with embedded capsular retreats cloistered around a light fixture

Fig. 001. Communal web with embedded capsular retreats cloistered around a light fixture

Between the late-1980’s and mid-1990’s I serviced several commercial clients in Marble Falls, Texas on a monthly basis. Over time those clients changed hands and environmental consultants. By 1995 I had no clients in Marble Falls. For the past 19 years, I’ve rarely had the pleasure of visiting that beautiful city.

Now that’s changed. One of my current clients with commercial establishments all over Texas recently purchased a new entity in Marble Falls. I was elated when they called and asked me to handle its environmental consulting needs.

Twenty years ago, my arachnological skills were paltry. Over the past decade and a half, though, I’ve made modest gains in my understanding of these creatures. Spiders, I realize today, contribute in dramatic ways to the health and comfort of the human race, and my appreciation for the good they do grows daily.

Forgive me for playing a bit, in the next few sentences, with the English language. The temptation to do so is overwhelming: I wouldn’t have paid much attention to the spiders this paper describes had I seen them — as I once did — through the eyes of an arachnoignoramus. Though never a true arachnophobe, I’ve only been a committed arachnophile for about fifteen years, but — trust me on this — the more one learns about these organisms the more one grows to appreciate them. Non-arachnophiles don’t understand that, and likely suspect those who love spiders are certifiably crazy arachnomaniacs. Maybe we are.

Given that possibility, I might say that, on 29 November 2014, while peering through the eyes of one afflicted with terminal arachnomania, I spied the spiders grouped around this light fixture and was forced by that affliction to stop, inspect, and learn from them. The employees at that building may have wondered what on earth I was doing there, peering upward, taking photos, then uncapping a vial, extending it up to the ceiling and holding it there for a few seconds before lowering it down, staring inside, and replacing its cap.

At any rate, on that day, while conducting an exterior inspection at the commercial entity mentioned earlier, I first noticed the presence of this curious grouping of spiders, and then — on closer inspection — realized that they must be engaged in a primitive form of social cooperation. The spiders were, as mentioned, cloistered around a ceiling light in an exterior vestibule, each equidistant from the ceiling, and about equidistant from one another as well. I realized that, though it was not visible, there must exist an extensive communal web in which these spiders, each in separate retreats, were embedded. Each retreat was cup-shaped, with its open end — its mouth — pointed downward. The communal web, for its part, appeared to be constructed much like the cob webs produced by spiders in the Theridiidae family.

The webs of many theridiids — like, for example, the black and brown widows — are occupied by a single female. She typically sits head-down in the center of a relatively small, isolated, silken snare. The web I noticed in Marble Falls, however, was spread out so that it encompassed a significant portion of the vestibule’s ceiling. Photos of the communal web and some of the individual retreats embedded within it, all taken with an iPad Air, are posted above and below.

Fig. 101. Capsular retreat 01

Fig. 101. Retreat 01

Fig. 102. Capsular Retreat 02

Fig. 102. Retreat 02

Fig. 103. Capsular retreat 03

Fig. 103. Retreat 03

Fig. 104. Capsular retreat 04

Fig. 104. Retreat 04?

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The spacing of the retreats built by these spiders implied that each spider had staked out its own prey-capture zone. This suggested that the individual spiders don’t share the bounty reaped from their capture zones with other spiders in the group. If so, that would make their grouping more communal or subsocial, rather than genuinely social in structure. Foelix (2011, p. 318) refers to the widely accepted classification of spider sociality set down by Avilés, in 1997, as follows (the first four in the list are from Avilés; I’ve added a fifth, to include the solitary non-social spiders):

  1. Nonterritorial, permanent-social (quasi-social; Wilson 1971; e.g., in Anelosimus  eximius).
  2. Nonterritorial, periodic-social (subsocial; e.g., in Stegodyphus lineatus)
  3. Territorial, permanent-social (communal; e.g., in Philoponella republicana)
  4. Territorial, periodic-social (subsocial, e.g., in Eriophora bistriata)
  5. Territorial, permanent non-social (non-social, i.e. all the rest)

This list describes a pyramid that stratifies, by social interaction, all the 40,000+ species of spiders known to man. Most spiders fall into the 5th group. A smaller number of species are in group 4, still fewer are in group 3, and so on until, on reaching the 1st group, the number of species represented is quite sparse.

So, while many spiders exhibit some forms of social cooperation, only a few exhibit true sociality. Foelix points out that of all the spiders known, only about 20 species live together in peaceful colonies that fulfill the two main criteria of genuine sociality: cooperation in a. prey capture and b. brood care.

Bilde & Lubin (Herberstein, 2011; ch. 8), in distinguishing between solitary and group-living spiders, note that fewer than 80 species of spiders are known to live in groups, and of these, only 25 are known to exhibit true sociality. Besides the two criteria mentioned above, Bilde & Lubin point out that social spiders lack pre-mating dispersal, resulting in regular inbreeding in their colonies, and feature female-biased sex ratios.

What distinguishes social spiders and their subsocial, communal, and solitary kin is the permanence or periodicity of their aggregations, and the degree of cooperation that each spider contributes to and gets from the group. As the above list shows, a wide variation of sociality exists between one species of social spider and the next.

The most highly developed social spiders, however, are no match for the social insects. Those positioned first in the above list remain, by comparison with their insect brethren, no more than quasi-social, because no spider is known to have developed anything approaching the degree of sociality observed in the most advanced species of ants, termites, and bees. Bilde & Lubin also point out that, once sociality evolves little further speciation occurs. Social clades involving spiders are almost always terminal, though by contrast insects that transition to eusociality often results in species richness, increased habitat occupancy and biomass.

Regardless, spider sociality — while more primitive than that of social insects — is real. The highest degree of spider sociality permits individual members of the group to behave, perennially, as though the entire communal web is theirs to travel, loiter, and consume prey upon. When prey is captured all spiders in the vicinity help to subdue it, and all are generally free to partake of a portion of the resultant meal.

201. Dorsal view, full body

Fig. 201. Dorsal habitus

202. Ventral view, full body

Fig. 202. Ventral habitus

Fig. 203. Eyes

Fig. 203. Eyes

Fig. 204. Sternum

Fig. 204. Sternum

Fig. 205. Epigynum

Fig. 205. Epigynum

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Now, as mentioned earlier, the spiders I found in Marble Falls are not truly social. Further, they are not theridiids; the presence of what appeared to be a tangle web notwithstanding, their anatomical characters are inconsistent with spiders in that family. I was anxious to learn, first, the family of spiders to which they belong. Next, I wondered what the individual spiders in the group gain by associating with one another.

Let’s attend to the first of these questions. Once we learn the identity of this spider we’ll then be privy to the extant scientific literature in its regard.

General Taxonomical Characters

To start, we must be able to categorize the simplest anatomical characters of this spider. That process began with collecting a specimen from the communal web and preserving it in alcohol. I did that by uncapping a 15ml glass vial of ethanol and lifting it up, just underneath one of the cup-shaped retreats. The first time this was done that spider vacated its retreat, conducted a ritualistic dance that appeared designed to scare away the interloper (me), then scampered up into the midst of the communal web. The next retreat under which I placed the vial, however, dropped from the mouth of the retreat directly into the ethanol, suspended by a silken thread. It was that specimen that was later examined under magnification in the lab and photographed.

Significant portions of a spider’s body, namely the abdomen and the legs, become deformed when dried out. When preserved in alcohol their bodies retain most of the characteristics present in live specimens (coloration sometimes is affected, especially after being immersed in alcohol for long periods, but body shape is not.) I use natural 80-95% ethanol, i.e. for  preserving insect and arachnid specimens.

The preserved specimen was, as mentioned above, later examined in the lab. While doing so, I consulted several of the existing dichotomous keys that various authorities have constructed for just such an analysis.

Some analysis can usually be done with the naked eye, provided the spider is not too small. This specimen, though smaller than most, was still large enough to enable a cursory exam without benefit of magnification.

Fig. 205. Ventral abdomen

Fig. 206. Ventral abdomen

I knew, for example, that this spider was a member of the taxonomical Class Arachnida (as figs. 201-2 show, it’s an arthropod with eight legs). It’s also in the Order Araneae (it spins webs), in the Suborder Opisthothelae (the spinnerets, shown in fig. 206. are positioned at the hindmost part of the abdomen), and the Infraorder Araneomorphae (the fangs — though not immediately visible — are positioned in chelicerae shown in figs. 201-2 that do not project conspicuously outward, in front of the face, as do those of the Mygalomorphae).

At this point the naked eye was of no further use, and the microscope became indispensable. I used, for that purpose, a digital AM4815ZTL Dino-Lite Edge dissecting microscope with a magnification range of 15-236x.

Under magnification it was clear this specimen was, first, a female, and second, a member of the Series* Entelegynae. The epigynum, shown in fig. 205, is sclerotized, having a distinct three-dimensional structure. Such structures are, in most entelegyne spiders, somewhat unique to each genus.

I presumed, too, that this specimen was in the in the Superfamily Araneoidea (as fig. 203 shows, it has eight eyes). Some may wonder at the necessity of counting the eyes. Suffice it to say that, unless the eyes are examined under magnification their number and orientation cannot be ascertained within an acceptable degree of accuracy. Though most spiders have eight eyes, some have but six, and a few have even less. Arrangements of the eyes vary considerably from family to family and within the genera of each family. The arrangement, or pattern and the relative diameters of a spider’s eyes in their various positions, i.e., the posterior medians (PME), posterior laterals (PLE), anterior medians (AME), and anterior laterals (ALE), almost always figure in the taxonomical identification processes.

Ubick et al.’s 2005 Taxonomical Key

Beyond this point, even with a microscope my search began to get more complicated. The choice of which dichotomous keys to use assumed supreme importance. For years the key provided in Ubick, et al., 2005 (pp. 25-38 for identification to family) has been a kind of gold standard for this purpose. It remains so — at least for me — today, though during the past nine years many revisions have been made to family and genus designations within the Order Araneae.

I recently asked Darrell Ubick, via email, if plans were being made to revise the 2005 edition of Spiders of North America. He replied that work on the revision is now underway, and the second edition of that book should be ready for publication within a year or so. I greeted that news with enthusiasm, and immediately purchased two brand new copies of the first edition, realizing it will soon be out of print. This book blazed new trails in the world of arachnology. The first edition will forever be a prized item in my library. But I digress…

Using Ubick et al.’s published key, I began on page 32 (having already progressed to the point of knowing this is an entelegyne spider). Here, under the heading Entelegynes, I read the first couplet, 57, whose first choice is “Chelicerae fused at base, eyes in three groups…” Though it cannot be determined, from the microscopic examination performed thus far, if the chelicerae of this specimen are fused or not, it is clear the eyes are not in three groups. The eyes depicted in fig. 203 form two rows: one — anterior, composed of four eyes — follows a more-or-less straight line across the lower face; the other — posterior of the first but also of four eyes — follows a curved line bent backward (i.e., recurved; the opposite of procurved, which describes a curvature bent forward).

I also noticed, for future reference, that the four median eyes (the posterior median eyes, or PME, at the top center of the eye group, plus the anterior median eyes, or AME, at the bottom center of the eye group) form a trapezoid (a convex quadrilateral with at least one pair of parallel sides, in this case the upper and lower sides being parallel) that is narrower at the top than at the bottom.

A note of caution and food for thought: I refuse to get stymied, when following a dichotomous key, on encountering an anatomical character that I’ve have not yet examined. If that character is the only one in the couplet, there may be no choice but to conduct that not-yet-done exam before proceeding. Often, though, one or more other characters will be supplied in the couplet, and some or all of them will already be known. If any one of those is described as a definite prerequisite but does not match the specimen under examination, the second choice in the couplet likely applies.

In this case, that second choice reads “Chelicerae not fused, eyes not so arranged, legs usually shorter with rigid tarsi.” The legs of this specimen are not exactly short, but “shorter than what?” Context matters. If one follows the first choice in couplet 57 one reaches the Pholcidae, also known as daddy-long-legs. This specimen has relatively long legs, but much shorter ones than those exhibited by the Pholcidae, so, with some confidence I proceeded on to couplet 58.

Couplet 58 deals with the number of trichobothria on the specimen’s tarsi, the last segment of the leg (metatarsus and tarsus). If no trichobothria, or at most one, is present, the first choice applies. If more than one is present, the second choice is followed. Trichobothria are stout setae, or hairs, which are more or less the same width their entire length, but that stand out from the smaller body hairs and are used to sense airborne vibrations or currents. Though trichobothria are found on the metatarsi of the legs of this spider, the tarsi are free of them. Thus I proceeded on to couplet 59.

Couplet 59 deals with the structure of the spider’s spinnerets and the arrangement of the eyes. Choice 1 is followed if the posterior lateral spinnerets have a long apical segment, and the eyes are clustered at a mound at the center of the cephalon (the head). Neither applies to this specimen, so I proceeded on to couplet 60.

Here the anterior tibiae and metatarsi have or don’t have a prolateral (projecting from, or on, the side facing forwards) row of curved spines in serrated series. The spines on the specimen’s tibiae and metatarsi are scattered, not in a row, directing me to couplet 61.

Here the tarsus on leg IV has a ventral comb of serrated bristles (but sometimes this is absent or indistinct), the legs usually lack spines, the chelierae usually have a basal extension (a tooth at its proximal end, hidden under the clypeus, and not visible in our specimen), and the epigynum is without a scape. The only sure part of this couplet that applies to this specimen (though in the negative) is that its epigynum clearly has a scape; its the hardened nipple projecting outward in the center of the image depicted in fig. 205. So I continued on to couplet 63.

Here the choices are remarkably simple: either the tarsi are as long as or longer than the metatarsi, or they are shorter. In this specimen the tarsi are much the shorter of the two, which directed me to couplet 65.

Choice 1 in couplet 65 applies if the sternum has a pair of pits at the labial margin, tibia IV has long trichobothria, the legs are stout, and the size is less than 2.5mm. Maybe the sternum has pits… but I couldn’t see any. What I could see was that the specimen has relatively thin legs, and is more than 2.5mm long, which took me to couplet 66.

Choice 1 in couplet 66 requires the clypeus (the space between the anterior edge of the carapace and the anterior eyes, i.e., the “lip” above the chelicerae) to be higher than three diameters of the anterior median eye along with several other not-easily-ascertained characters which I felt could safely be ignored, inasmuch as the clypeus of our specimen is quite narrow. Thus I continued on to couplet 68.

Couplet 68’s first choice applies if the specimen has square or rectangular endites (the expanded lobe of the palpal coxa, situated laterally of the labium), the epigynum is usually three-dimensional with a scape, and the spider is known to build a vertical, orb-shaped web. Not much could, at the time, be said about the endites, as they are quite dark and it is difficult to see their margins clearly. It was known the epigynum is three-dimensional and has a scape. I have little information on the kind of orb web it builds, if in fact it builds an orb web at all.

Accepting choice 1 directed me to the Araneidae family. These are the well-known orb weavers of garden and forest that arachnophiles love so much. That choice does not seem to fit this spider very well, yet it appeared to be the best of all the remaining alternatives. The second choice, for example, took me to the Tetragnathidae. I won’t bore you with the details but suffice it to say that a thorough perusal of that latter family — which I’m somewhat familiar with —failed to produce anything resembling our specimen.

Onward, then, to the Araneidae, using the key to araneid genera beginning on page 69 of Ubick et al., 2005.

Couplet 1 requires the investigator to ascertain whether the posterior median eyes are posterior to the lateral eyes in dorsal view. They are not, which took me to couplet 4.

Couplet 4 asks if the carapace is tuberculate posteriorly, with two branched tubercles. It is not; the carapace of our specimen is smooth. This took me to couplet 5, which asks if the third tibia has a cluster of feathery trichobothria, and if the thoracic region is high, with a median longitudinal line. Neither character applies, taking me onward to couplet 6 which asks if the female abdomen has spines. This specimen’s abdomen is without spines, taking me to couplet 7, which inquires if the abdomen has a notch at its posterior end. Not on our specimen. This took me to couplet 9, asking if the abdomen is attached to a pedicel near its middle (which would orient the abdomen nearly vertically in lateral view) or near its anterior end. The abdomen of this specimen attaches to a pedicel near its anterior end, taking me to couplet 13, which asks if the specimen’s abdomen has one to three posterior conical projections, and if the posterior median eyes are spaced their diameter or less apart; No to each, which took me on to couplet 14. Here it is asked if the abdomen is orange; It is not, and that took me to couplet 15.

Couplet 15 questions if the abdomen has spines or tubercles on the sides and/or posterior; No, to both. This skipped me forward to couplet 19 which asks if the abdomen has a distinct dorsal pattern of two lines, the outer one being diamond-shaped; No, not on our specimen. This directed me to couplet 20, which asked if the ventral abdomen has a median light-colored longitudinal band. Yes, this specimen does have such a band. That took me on to couplet 21.

Couplet 21 asks if the abdomen is elongated; No, the specimen’s abdomen is oval and short. I was thereupon directed to couplet 22.

Couplet 22 inquires whether the metatarsus and tarsus are, together, longer than the patella and tibia, and if the abdomen has a dorsal folium (leaf-shaped markings); I cannot speak to the first part, as I’ve not yet precisely measured these anatomical characters, but I can speak affirmatively to the second; our specimen has a folium. This directed me to the genus Metepeira. Now, that would not have been quite so exciting except for the fact that two of the drawings (17.34 and 17.35, both the handiwork of Nadine Dupérré, who prepared all the excellent drawings exhibited in Ubick et al., 2005) referenced on page 72 in couplets 20, 21 and 22, depict our specimen exactly.

From this result I feel confident in concluding that this spider is very likely a member of the genus Metepeira. However, inasmuch as its habits, and the webs it builds seem inconsistent with the araneid orb weavers, I realized more investigating needed yet to be done to determine if spiders in this genus behave this way.

William H. Piel’s Systematics of the Genus Metepeira

A detailed paper on Metepeira systematics was published by Herbert Levi, in 1977. That paper, though responsible for blazing new trails in our understanding of spiders from three related genera, Metepeira, Kaira, and Aculepeira, is now out of date.

A revision to the genus Metepeira, prepared under the tutelage of Herbert Levi (who, sad to say, passed away on 3 November 2014, with his wife and life partner, Lorna Levi, passing only 11 days later) and Edward O. Wilson, was published by William H. Piel, in 2001. Piel’s paper was part of his PhD thesis for the Department of Organismic and Evolutionary Biology, Harvard University. That publication, though now out of print, is accessible online via archive.org. A link to it is provided in appendix 2, below, under Piel, 2001. In the introduction to his paper Piel notes that 39 species and 3 subspecies of the genus Metepeira were recognized at the time of his writing. Today (2 December 2014) the World Spider Catalog lists 44 species and no subspecies for this genus.

Before discussing Piel’s revision, a few words about Levi’s 1977 paper are in order. Levi maps the specimens of Metepeira he studied on pages 194 and 197, showing five species as having been collected in Texas. One of these, M. minima, was found only in the extreme southern tip of the state, and two others, M. arizonica and M. foxi, were found only in the Pecos. Two others, M. labyrinthia and M. comanche, were shown to be distributed widely throughout Texas.

Both of these latter two species are described by Levi (pg. 199, fig. 4 for M. labyrinthia, and pg. 207, fig. 69 for M. comanche) as possessing a median longitudinal white stripe on both the venter and the sternum, consistent with the specimen I describe here from Marble Falls, except that fig. 69, depicting the ventrum of a M. comanche female, shows a transverse bar that connects to the posterior extremity of the venter’s longitudinal stripe, which is absent in the M. labyrinthia female. In the text (pp. 204-6) he describes this transverse bar as often (though, by implication, not always) present.

Levi points out that M. labyrinthia and M. comanche are sympatric. That is, they are believed to have evolved from the same ancestral species while inhabiting the same geographic region. The two species differ, according to Levi, in a number of subtle anatomical characters in addition to the latter often displaying the transverse bar mentioned above, which characters he describes in some detail.

Piel points out that great ecological and behavioral interest has existed for some time regarding this genus of spiders. Many are obgligate (necessarily) or facultative (optionally) social species whose habits provide models for investigations into genetic and environmental factors that influence colony formation. It is important, Piel tells us, that students of this genus ascertain the exact species they are working with when gathering data on their behavioral traits. Unfortunately, though, their relatively small, indistinct genitalia and generally homogeneous abdominal patterns have made it difficult to distinguish between individual species in the field.

The web constructed by members of this genus consists of a barrier or scaffolding structure surrounding a classic araneid orb with a retreat suspended in air. Except for the apparent absence of a classic araneid orb, that description is consistent with the webbing observed with this specimen.

Piel makes much of the lighter areas around the eyes. I could see that in this specimen. He points out that the posterior median eyes are from 1.1 to 1.7 times the diameters of the anterior medians, that the posterior medians are closer together than the anterior medians (remember the trapezoid those eyes form, narrower at the top, broader on the bottom? this confirms that character is consistent with this genus), and that the anterior medians are closer to the lower edge of the clypeus than their diameters. Again, these characters appear to be consistent with this specimen (see fig. 203), though I cannot, from the photos I presently have, establish the differences between the diameters of each set of eyes (this will be done before long).

He describes the presence of a median, longitudinal white line on the ventral abdomen as uncommon among the araneids, and the combination of a similar white line on the sternum (present in some but not all Metepeira species, but present in this specimen), as a unique character not found in any other araneid.

Except for M. datona, and sometimes with M. desenderi, Piel asserts that all species in this genus have a combined metatarsus and tarsus that is longer than the combined patella and tibia. This character is rarely found in other araneids, even in likely relatives such as the spiders in the genus Kaira F.O.P.-Cambridge. For this reason, determining whether or not it applies to our specimen is important. To accurately measure this character in our specimen, however, I must detach the legs and mount them on a slide; that will be done sometime in the future, once additional specimens have been collected.

Rings on the leg articles are conspicuous in this specimen, and according to Piel are common in most species of the Metepeira. In mainly tropical and high-altitude species the coxae are mostly black, but in desert/mesquite species they are yellowish-white. In this specimen the essentially dark coxae for legs I and II are clothed with whitish-yellow hairs, while those of coxae III and IV are nude, and thus darkened in coloration, which appears to be mid-way between the two extremes Piel described. Perhaps, then, this species is one that prefers habitats that are neither tropical nor arid. Marble Falls meets that criteria.

Macrosetae (pointed spines in sockets) are usually concentrated on spider leg articles that contact other spiders during mating or grappling. This translates, for most spiders, into a concentration of macrosetae on tibia II. In the Metepeira, however, the macrosetae are concentrated on femur I, with females having 2-5 o the anterior femur and 0-7 on the anteroventral (in front of and toward the lower surface) side. In this specimen several macrosetae can be observed in figs. 201 & 202, with the greater number concentrated on femur I than on femur II.

Though under magnification the epigynum of this specimen appears to be strongly sclerotized, Piel notes that in the Metepeira it is fleshy and its degree of sclerotization is weak. I take this to mean that, if manipulated with a probe, it is pliable. His drawings depict an epigynum that is fully consistent with that of our specimen, particularly with regard to M. comanche (Piel, 2001 pg. 61), which besides exhibiting a remarkably similar epigynum also has a white line on both the sternum and ventral abdomen. It must be noted that Piel has very little to say about the species M. comanche. The implication is that little is known about it, in comparison with many of the other species his paper discusses.

Metepeira produce Unique Webs

Piel asserts that the web built by all Metepeira species combines an orb with a barrier web. This uniqueness was asserted by Levi in 1977, and again by Lopez, in 1993. As with two other notable genera in the Araneidae — Cyrtophora Simon and Mecynogea Simon — these spiders construct a retreat (which Piel does not describe in detail) that hangs in the air, away from substrate, suspended by the scaffolding afforded by the barrier web. A signal line attaches the retreat to the hub of the orb web. This dual-function line transmits vibrations from, and provides the spider efficient access to, the orb. Egg sacs are tan colored, and are usually strung together above the retreat, with the most recently laid eggs nearest the retreat. The wording Piel uses here implies the egg sacs are distinctly separate from the retreats. A closer examination of this colony may reveal the presence of such egg sacs, but the photos presently available do not appear to show them clearly (small, decorated clumps of webbing can be seen, though, and may be the egg sacs Piel mentioned). The more extensive tubular structure shown in fig. 104 may be a retreat (though no spider was observed at its entrance) or a string of egg sacs. This structure was to be examined more closely on my next visit to this facility, but — alas — on that next visit (on December 23rd) the webs, retreats, and spiders were gone, victims of the cold weather in between. In 2015 they should be back and, with luck, I’ll encounter them again and continue this study.

 Suspended Retreats and Barrier Webs may facilitate Colony Formation

Piel notes, citing Gillspie. 1987 and Rypstra, 1986. that plentiful supplies of food lead to increased tolerance for one another, and an increased tendency to aggregate. He further asserts, citing Burgess and Witt, 1976, and Uetz, 1986, that the suspended retreats and barrier webs of Metepeira, Cyrtophora and Mecynogea, may encourage aggregations of conspecifics. This results, it is believed, from an easing of their dependency of substrate availability and the provision of a common support system.

More to come…

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*Note that whenever one progresses beyond the simplest, most accepted taxonomical terms (Phylum, Class, Order, Family, Genus and Species), the authorities often disagree on how to title those additional terms. Don’t get bogged down with terminology. The key is the hierarchy of the terms being used, and here “series” comes between “infraorder” and “superfamily.” That is, it is a further delineation of all the organisms in the infraorder that came before, and is  broken down further by the list of superfamilies beyond it.

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Appendix 1. Taxonomy:

  • Kingdom Animalia (an-uh-MAYHL-yuh) — first described in 1758 by the Swedish taxonomist Carolus Linnaeus (1707 – 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 to animals with jointed feet, but in the more narrow context of the invertebrates, which have segmented bodies as well as jointed appendages;
  • Subphylum Chelicerata (Kuh-liss-uh-RAH-tah) — first described in 1901 by the German zoologist Richard Heymons [1867 – 1943] using the Greek noun χηλη (KEY-lay) = 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,” but broadly referring 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;
  • Suborder Opisthothelae (oh-PIS-thoh-THEE-lee) — first described in 1990 by the American arachnologists Richard C. Brusca and Gary J. Brusca, who used the Greek words οπισθεν (oh-PIS-thehn) = behind, at the back, yet to come + θηλη (THEE-lee) = nipple or teat, to distinguish this grouping of spiders from the more primitive spiders in the suborder Mesothelae, in that certain characters (e.g., tergite plates, ganglia in the abdomen, and — in particular, inasmuch as the suborder name is a direct reference thereto — median-positioned spinnerets) of the latter are absent in the former; thus spiders in this suborder have spinnerets positioned at the hindmost portion of the abdomen;
  • Infraorder Araneomorphae (Uh-RAY-nee-oh-MOHR-fee) — distinguished from the mygalomorphae by having opposing fangs that open and close perpendicular to the spider body’s longitudinal axis, in a pinching action, whereas spiders in the infraorder mygalomorphae (e.g., tarantulas and trapdoor spiders) have fangs that open and close more nearly in alignment with the spider body’s longitudinal axis.
  • Series Entelegynae (inn-TELL-uh-jiy-nee) — araneomorph spiders which, unlike the Haplogynae, have hardened, i.e., sclerotized, female genitalia. Foelix (2011) points out that “entelegyne spiders have more complex reproductive organs (with an epigyne and separate fertilization ducts in the female)…” and that “Male entelegyne genitalia are very diverse…“; most members of the entelegynae have eight eyes, though some have reduced eyes are have lost their eyes altogether, and some, e.g., those in the genus Lygromma (Prodidomidae, Gnaphosoidea) have six eyes; some 27 superfamilies of spiders are grouped under the entelegynae;
  • Superfamily Araneoidea (uh-RAY-nee-OY-dee-uh) — comprised of 15 families of eight-eyed spiders, specifically:
    • Anapidae (Simon, 1895): Small spiders, most less than 2mm long, that generally live in leaf litter and moss on rainforest floors, many of which build small orb webs (less than 3 cm dia.);
    • Araneidae (Simon, 1895): Typical orb weavers, the most common grouping of spiders that generally, but not always, build round, planar, wheel-shaped webs;
    • Cyatholipidae (Simon, 1894): Mostly confined to Africa, living in moist, mountain forests, though some live in drier regions, including savannah;
    • Linyphiidae (Blackwall, 1859): Very small spiders generally known as sheet weavers, bowl and doily weavers, and money spiders;
    • Mysmenidae (Petrunkevitch, 1928): Distributed in the Americas, Africa, Asia, Europe, and New Guinea and several islands;
    • Nephilidae (Simon, 1894): Spiders that partially renew their webs, and that, therefore, do not regularly replace their webs entirely with new ones, as do the spiders in the Araneidae;
    • Nesticidae (Simon, 1894): Scaffold web spiders which, like the Theridiidae, have a comb of serrated bristles on the hid tarsi used to pull silk bands from the spinnerets;
    • Pimoidae (Wunderlich, 1986): A small, relictual, monophyletic grouping of spiders found along the western coast of North America, in the Alps, alpennines, and Cantabrian Mountains of Europe and northern Spain, and in the Himalayas; a species was found in Japan in 2003;
    • Sinopimoidae (Li & Wunderlich, 2008): one genus containing the single species Sinopimoa bicolor (Li & Wunderlich, 2008); suspected by some authorities to be a member of the Linyphiidae, in the subfamily Erigoninae;
    • Symphytognathidae (Hickman, 1931): contains one of the smallest spiders known, Patu digua (Forster & Platnick, 1977), though several other spiders of similar size have been found;
    • Synaphridae (Wunderlich, 1986): distributed mostly in europe and north Africa;
    • Synotaxidae (Simon, 1894): distributed mostly in Central and South America, New Zealand, and Australia;
    • Tetragnathidae (Menge, 1866): Long-jawed orb weavers, with elongated bodies, long legs, and elongated chelicerae; these spiders build small orb webs with an open hub, few wide-set radii and spirals, with no signal line and no retreat;
    • Theridiidae (Sundevall, 1833): Tangle-web, cobweb, and comb-footed spiders;
    • Theridiosomatidae (Simon, 1881): Ray spiders that build cone-shaped webs;
  • Family Araneidae (Simon, 1895) — air-uh-NYE-dee — Typical orb weavers, the most common grouping of spiders that generally, but not always, build round, planar, wheel-shaped webs;
  • Genus Metepeira (F.O.P.-Cambridge, 1903) — mett-ee-PYE-ruh — derived from the Ancient Greek μετα (“similar to”) and the obsolete genus Epeira, to denote the similarity between the spiders in this genus and Epeira.

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Appendix 2. References:

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