Notes on Zygiella x-notata

From The Newsletter No. 84 March 1999

In summer 1997, I collected an immature female Zygiella x-notata which was being guarded by a mature male.

Protandry (males maturing earlier in the season than females) is a feature of this species (Yoward, 1996), so this is a common phenomenon in late summer. I housed them separately until the female had moulted to maturity, then I introduced the male and observed them mating. The male was left with the female for several months whilst she laid eggs. During this time they were kept at room temperature and fed ad libitum on large dipteran maggots. The male lived until 7th March 1998—long after he would be expected to survive in the wild. Perhaps under more natural conditions males are killed by low temperatures; mate-seeking, male-male contests and mating itself certainly all also take their toll. However, sexual cannibalism does not seem to be the rule in this species; in fact the male described here lived off captures in the female's web and did not build a single web during the time they were together.

All four cocoons laid (on 27/10/97, 20/11/97, 11/12/97, 03/01/98) before the female died (on 04/01/98) proved to be fertile and hatched before liberation. When they hatched, despite the feeding regime being continuous, the male cannibalised what could only be his own offspring. This was probably due to the artificiality of the situation, because discrimination in prey choice by the male to avoid his offspring could not evolve in this species where the males are almost invariably dead long before their progeny emerge. Therefore this finding does not have the significance of Felton's (1969) observation of adult Pirata piraticus eating juveniles in the wild.

These observations do, however, suggest that a sedentary, well-fed, monogamous, thermally protected lifestyle may considerably prolong the span of male Zygiella x-notata, though in the wild 'living fast and dying young' may be evolutionarily more advantageous.

References
Felton, C. (1969) Cannibalism in Pirata piraticus (Clerck). Bull. Br. arachnol. Soc. 1: 23.
Yoward, P. J. (1996) Spider sperm competition: the conduit/culde- sac hypothesis—a route to understanding or a dead end? D. Phil, thesis, University of York.
 
Added by John Partridge at 20:26 on Fri 24th Feb 2012.

Notes on the Behaviour of Spiders During the Ice Age! by Lawrence Jones-Walters

The Newsletter No. 64 July 1992

A couple of years ago I visited the Chiltems Open Air Museum where, among other things, they have a fullsize reconstruction of an Iron Age hut. The building is roughly circular, with a conical, thatched roof and wattle hurdle walls. There is no opening in the roof to allow smoke to escape but, remarkably, when a fire is lit in the simple hearth it filters slowly through the thatch, filling the roof space but leaving a smoke-free zone below a height of about five feet from the earth floor. The thatch is probably home to a range of animals and plants and includes a large population of Zygiella x-notata. Otherwise relatively inconspicuous, when confronted with the dense smoke of the fire they lower themselves on a single precarious thread to a point just below the level of the fumes. There they remain until conditions improve: a clue to the behaviour of their ancestors and, no doubt, further confirmation to those people of ancient times of their apparent 'wisdom', which had placed them in the folk-lore and mythology of almost every major culture, past and present.
 
Added by John Partridge at 16:01 on Tue 20th Dec 2011.

Unusual Web Structure in Zygiella x-notata by Andrew West and Stephen Hopkin

From The Newsletter No. 64 July 1992

The roof of the Zoology Department at Reading University is home to a great number of spiders. Zygiella x-notata is particularly common, their webs easily recognised by the missing sector in the upper half. The web is usually secured by means of a single thread which extends down to, and secures with, the floor. Recently, however, an unusual variation on this theme was observed at Reading. The base of the web was not in contact with the ground but was held in tension by two threads attached to a small stone hanging in midair giving the appearance of a pendulum-like structure. This was not a unique web. At least three other Z. x-notata have constructed a web of this type in other areas of the roof. Furthermore, the same spider incorporated the same stone into its web over three consecutive days following daily destruction of the web by one of us (A.W.). The stone varied in height above the ground from 15 to 100 cm. Webs which incorporated stones into the webs seemed to be in positions that were most exposed to the wind (the building is eight storeys high). We would tentatively suggest that webs which make use of hanging stones are more resilient than those moored by a single thread to the ground. Most webs weighed typically between 0.1 and 0,5 mg, but were capable of supporting a stone of almost 500 mg. The plasticity exhibited in this type of behaviour lends support to the argument that web building is not an entirely stereotyped process. is not an entirely stereotyped process.

Note that the original article had two illustrations
 
Added by John Partridge at 15:20 on Tue 20th Dec 2011.

The Presence of the Missing Sector by Dick Jones From The Newsletter No. 69 March 1994

It is always a great disappointment to travel to exotic locations and find spiders which one can see from the comfort of one's own living room (Dalingwater, 1993). For a Portsmouth resident, Southampton is less tropical than for a Mancunian, but in Mallorca, southern Spain and the Canary Islands I have eagerly collected specimens of what transpired, under the microscope, to be Zygiella x-notata.

Perhaps I was deceived by the remoteness of their webs from houses. Specimens were collected from rocks well away from human influence, and this led me to wonder about their natural niche. Houses are a relative novelty for spiders, so those which are only found around them in this country have been a puzzle to me. I never found more than occasional, isolated specimens on holidays, compared with the hordes I find on my window frames, so I suspect the more marginal habitat may give a clue to their ecology. Rather than starting with the web, my thoughts start with the spider.

Zygiella has evolved to function as a retreat-making orb-weaver in a confined, vertical space, unlike many other species, which must have some depth behind the web. Its preferred substrate is inflexible with small protrusions where the retreat can be fixed: a vertical rock face with overhangs is ideal. Thus it acquired the facility of leaving a gap in its orb web to allow the signal line to be in the same plane, whilst being clear of it. Not surprisingly, the spider has been able to colonise window frames, where a passable imitation of the natural habitat has been inadvertently duplicated many times over.

The design of the open sector web is the only solution to the problem of having a signal line and retreat which are nearly in the same plane as the web. It is the only way in which the spider can run between hub and retreat without snagging the web. When the retreat is at an adequate distance from the web plane, the missing sector is filled with spiral lines, although often not at the same density as the rest of the web. Webs made under gutters, and in other deep recesses are in this form.

Araneus alsine 'bridges the gap' between Zygiella and species like Zilla diodia, Mangora acalypha and Argiope bruennichi which occupy the hub at all times. It makes its web at ground level or in low bushes, and leaves the upper two sectors open and hangs a small leaf in the gap. A few lines span across the top for stability. The spider is well hidden, and close to (if not actually on) the hub, ready to catch its prey.

If one examines a Zygiella web carefully, the spirals are often continued along the radii adjacent to the signal line, and back again to the next spiral. How the spider detects the signal line is a matter of conjecture, as all the spiders on my windows make their webs in the early hours of the morning, so I have never seen them at work. Perhaps the tension in the signal line is greater than that in the radii, and once it is touched, the spider is stimulated to reverse, and continue the spiral in the opposite direction. Even in their narrow habitat, the signal line is rarely at exactly the same angle as the radii, so this might be an alternative cue. The spiders have prospered and their numbers now exceed even the many artificial rock faces we have provided. Frequently they overflow on to nearby shrubs, but this substrate is foreign to them; I once saw a web on a bush which had been made 'upside down', with the retreat below the hub.

Zygiella atrica seems to have evolved to do the same trick on less rigid supporting structures, and Z. stroemi in much smaller spaces than Z. x-notata. On Lanzarote, I have found Z. minima Schmidt, living amongst volcanic boulders near the sea. These have many deep holes in them, caused, I imagine, by gases escaping during their formation. The spiders use the holes as retreats, and very effective they are too, as I was unable to extract more than three specimens from amongst dozens of webs. Long bridge lines stretch to the next boulder, with a small, typically Zygiella web situated near the middle. The long signal line goes back to the retreat in the same plane as the rest of the web.

I have not been able to see any seasonal variation in the webs of Z. x-notata, but I have seen sparrows hovering at my windows, trying to spike the unfortunate spiders from their retreats. Perhaps those in such exposed conditions are predated more than the spiders which are more hidden from the birds. Thus those that survive longer will have retreats further from the web plane, and not have missing sectors in their webs. I suggest that it is the nature of the immediate surroundings which influences the web design, although John Dalingwater's suggestion of the advantages of a larger catching area in a leaner season is very appealing, but surely a consequence of the spider's less exposed situation.

One interesting aspect of the life history of Zygiella x-notata is the great length of the season of the adult females (as compared with Araneus diadematus). The females of both species are adult at about the same time in the early autumn. But even unmated diadematus do not survive out of doors much after Christmas (a large female in a conservatory during the winter of 1992 was last seen on 6th January; the web had not been replaced for about a month). Those which lay eggs do not as a rule see November. Z. x-notata carries on much as normal throughout the winter. They continue renewing their webs at irregular intervals, and can be seen on the hubs at night, even when the temperature is below freezing (a habit which can also be seen in Nuctenea umbratica). They appear to catch very little during the cold season, in spite of renewing their webs periodically.

Z. montana (C. L. Koch), which I collected in the Pyrenees, has much the same substrate preferences to Z. x-notata, but usually at a much higher altitude. It is able to live in a harsher environment than its congeners by taking several years to reach maturity. This appears to be a natural development from the longevity of Z. x-notata and is paralleled by Meta menardiand M. bourneti which have poorer hunting grounds than their near relatives. The oldest female Z. x-notata I have found was taken in June, though I do not know whether this had laid eggs or not. This individual would have had an adult life span of about 10 months, compared with an absolute maximum for A. diadematus of 5 months.

Reference Dalingwater, J. (1993) Absence of the missing sector. Newsl. Br. arachnol. Soc. 66: 8. 63,

Editor's Footnote: Peter Merrett has pointed out that Bristowe discussed filling in of the 'missing sector' in both The Comity of Spiders (1939) and The World of Spiders (1958), There is no new thing under the sun!

 
Added by John Partridge at 15:13 on Tue 20th Dec 2011.

Absence of the Missing Sector by John Dalingwater From The Newsletter No. 66 March 1993

In Southampton we looked for Zygiella in typical situations on door and window frames and found that the characteristic 'missing sector' of the web had been filled in with catching spiral threads. I had seen this phenomenon before, in Swansea in late September. Presumably the function of the missing sector is to allow the signal line to take the shortest possible pathway to the centre of the web and to facilitate the spider's passage to the outer surface of the web. Perhaps later in the season these advantages are outweighed by the loss of catching area, and so the spider fills in the sector and angles its signal line. Is this a seasonal phenomenon, a regional variation, a modification to suit a particular situation in which the web is built, or are there other explanations?
 
Added by John Partridge at 15:23 on Wed 28th Dec 2011. Return to Summary for Zygiella x-notata