Zygiella spp

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Zygiella x-notata (Clerck, 1757)

Zygiella x-notata


Contents

Etymology:

Zygiella F. O. Pickard-Cambridge created the name as a feminine diminutive of Zygia as used by C. L. Koch, which was preoccupied in the Coleoptera. Cameron (in Spiders of North America (Ubick, et al, 2005)) thinks that Koch was referring to the goddess Hera (Ζύγια).

x-notata (Latin) with an x-shaped mark . Roberts (1985), in his Harley book, notes that "(t)he specific name was used by Clerck because ‘the astronomical character of the sign Pisces, or a letter X, is seen on the upper or forepart of the abdomen’. I have never seen it."

General:

This species is the most common of our missing-sector orb weavers and familiar to most people, even if they don’t realize it.

Description:

This genus has been included in the Tetragnathidae but is now included in the Araneidae. The members of this genus differ from many of our other Araneidae in having a more elongate, slightly flattened abdomen. Z. x-notata has a dark, broad median longitudinal band on the prosoma, wider anteriorly, on a lighter yellow-brown background. The dorsal surface of the abdomen is covered in a broad band with indented edges (the folium), white-edged with a darker interior and a lighter median line. The lighter areas of the abdomen often have a silvery sheen. The legs are annulated.

Distribution and habitat:

FIGURE 1. Simplified distribution of Zygiella x-notata. The darker the shade of brown, the more records of the spider. Based on the data in the Provisional atlas (Harvey et al, 2002).

Nationally Zygiella x-notata is widespread. It is usually found around buildings and structures, and its apparent distribution in the UK reflects this with the highest densities of records in the heavily populated urban areas. The species has its centre in Europe, but is cosmopolitan, probably having been transported around the world by man.

General life history:

Most Z. x-notata are adult from July to about October, the males peaking in number in September and the females slightly later. A number of adult females can be found active into December and beyond.

Mating occurs in September. Tarsitano and Kirchner (2001) studied the courtship of Z. x-notata, measuring and describing the vibrational signals the male sends to the female via her web. One of the signals, which the male produces on first encountering the web and approaching the female, was described as "burping", named for how the signal sounded when transduced, by the measuring equipment, to something audible! Despite this, the males still successfully mated.

After mating the males soon die. Egg-sacs are produced in September-October, (some even in the winter months), with the spiderlings emerging in early spring.

Other members of the genus:

The other members of the genus, present in Britain, are Z. atrica and Z. stroemi.

Z. atrica tends to avoid buildings and structure, building its web in shrubs and bushes.

The rarer Z. stroemi is more restricted in its habitat. It builds its web, more delicate than the other British members of the genus, in well-established woods, making its retreat in the deep crevices of the trunk of well-fissured trees such as Oak and Pine (Hambler, 1987; Jones, 1981) and generally on the warmer, southerly facing side of the tree.

Several other species occur in continental Europe: Z. keyserlingi, Z. kochi and Z. montana.

Missing sector webs:

Zygiella species are renowned (at least amongst arachnologists) for building missing sector orb-webs
Zygiella atrica web showing the missing sector.
. Why do they build such webs? How do these webs improve the species’ evolutionary fitness; and, if there is an advantage, why don’t all spiders build missing sector webs?

On first thought the loss of a significant fraction of the capture area of the web might be considered a disadvantage; how does a missing sector offset this?

The missing sector is actually where the signal thread is placed, the thread that leads from the web’s hub to the spider’s retreat where the spider spends the daylight hours. When a prey item hits the web the spider is notified via the vibration of this signal line, rushes to the web’s hub, locates the position of the prey and then moves out from the hub to deal with it. When dusk falls the spider emerges and sits at the hub of the web. So the missing sector seems to be there to accommodate the signal line. It is thought that the missing sector allows more rapid access to the hub from the retreat, and vice versa, a more rapid withdrawal to the retreat. Tilquin (1942, quoted by Grasshoff and Edmunds, 1979) noted that Zygiella can reach its hub faster than Araneus redii, but did not ascribe an advantage to it. However, Grasshof and Edmunds (1979), in their work on Araneus legonensis argued otherwise. Heiling (2004) didn’t work with Zygiella but did look at the effect of spider position (in its retreat or at the hub) and of web asymmetry on Larinioides’ prey capture performance. By manipulating the position of the retreat she was able to show that the web was built so that it was generally smaller on the side adjacent to the retreat. Her results can be interpreted as showing that more rapid access to the web hub is an advantage, confirming Grassoff and Edmunds’ idea.

As it seems to be a characteristic of Zygiella species to construct missing sector webs, they must have hit upon the web-building technique early in the evolutionary history of their genus. Having found their own optimal peak in the evolutionary landscape (using Sewall Wright’s description, see Dawkins’ "Climbing Mount Improbable"), they seem to have dug themselves even further into the landscape, fairly well excluding other neighbouring genera, or perhaps their neighbours are comfortable enough on their own peaks of local optimality. Actually there’s a panoply of modified orb-webs from the ladder webs of Tylorida and Scoloderus (Foelix ,1996, p. 132, Stowe, 1978) through Cyrtophora’s communal webs down to the bolas spiders’ single strand [1] so the landscape must be a rugged one, littered with peaks of local optimality! Compared with many of these, Zygiella’s web seems fairly minimally modified and other genera have been described which have "missing" sectors (e.g. Araneus legonensis (Grasshoff & Edmunds, 1979) and some species of Metazygia (Levi, 1995)). And, in fact, Zygiella isn’t obliged to build missing-sector webs, individuals often building full orb webs. Wiehle (1927, quoted by Grasshoff & Edmunds) observed that if the signal thread made an angle >40° with the plane of the web then Zygiella constructed a complete orbweb. Marples & Marples (1971) studied Zygiella in a Hampshire garden and confirmed that Zygiella building webs in bushes built full webs if the signal thread made a large enough angle with the plane of the web (though they didn’t distinguish between Z. atrica and Z. x-notata). Webs built in door or window-frames generally possess a missing sector as the retreat and web are constrained to lie in the plane of the frame.


As Zygiella is flexible as to whether it fills in the missing sector or not this seems to imply that the spider must know the whereabouts of its retreat before it builds its web. Either that or it removes the missing sector after having built a complete web. Zschokke [2] has carried out extensive work on web building by spiders and he notes that Zygiella can construct the missing sector either by never filling in the sector, reversing its direction at the sector when laying the spiral, or it can build a complete web and then remove the spiral within the sector by biting through the threads. Web building in spiders is instinctive but it does appear that Zygiella is relatively flexible in its behaviour.

References:

Foelix, R. F., 1996, The Biology of Spiders, 2nd edition, Oxford University Press.

Grasshoff, M. and Edmunds, J. 1979: "Araneus legonensis n. sp. from Ghana, West Africa, and its free sector web". Bull. Br. Arachnol. Soc. 4(7), 303-309.

Hambler, C. (1987) "Zygiella stroemi (Thorell) on Oak." Newsl. Br. arachnol. Soc 50: 2-3.

Harvey, P. R., Nellist, D. R. & Telfer, M.G. (eds), 2002, Provisional atlas of British spiders (Arachnida, Araneae), Huntingdo,: Biological Records Centre.

Heiling, A. M., 2004, "Effect of spider position on prey capture success and orb-web design", Acta Zoologica Sinica, 50(4), 559-565

Jones, D. (1981) "Zygiella stroemi (Thorell)." Newsl. Br. arachnol. Soc 30: 9-10.

Levi, H. W. 1974: "The Orb-weaver Genus Zygiella (Araneae: Araneidae)". Bull. Mus. Comp. Zool. (Harvard University), 146 (5), 267-290.

Levi, H. W.; 1995; "The neo-tropical orb-weaver genus Metazygia (Araneae: Araneidae)"; Bulletin of the Museum of Comparative Zoology, 154, 63-151. [3]

Marples, B. J. and Marples, M. J. 1971: "Notes on the behaviour of spiders in the genus Zygiella." Bull. Br. Arachnol. Soc. 2(2), 16-17.

Roberts, M. J., 1985, The Spiders of Great Britain and Ireland, Harley Books, Colchester.

Stowe, M. K., 1978, "Observations of two nocturnal orbweavers that build specialized webs; Scoloderus cordatus and Wixia ectypa (Araneae: Araneidae)", J. Arachnol. 6, pp. 141-146 [4]

Tarsitano, M. and Kirchner, W. H. 2001: "Vibrational courtship signals of Zygiella x-notata." Bull. Br. Arachnol. Soc. 12(1), 26-31.

Tilquin, A., 1942, "La toile geometrique des araignes", Paris, Presses Universitaires.

Ubick, D., Paquin, P., Cushing, P. E. and Roth, V. (eds.), 2002, Spiders of North America: an identification manual, American Arachnological Society.


Links to the Spider Recording Scheme's Zygiella pages:

http://srs.britishspiders.org.uk/portal.php/p/Summary/s/Zygiella+atrica

http://srs.britishspiders.org.uk/portal.php/p/Summary/s/Zygiella+stroemi

http://srs.britishspiders.org.uk/portal.php/p/Summary/s/Zygiella+x-notata

External Links

Note: BAS cannot verify the accuracy of any information on these external links

Links to other sites with info on or images of Zygiella x-notata:


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