Tegenaria gigantea saeva

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Tegenaria saeva Blackwall, 1844 and Tegenaria gigantea Chamberlain & Ivie, 1935

Tegenaria gigantea male

(Note: Tegenaria gigantea is also referred to, in some recent sources, as T. duellica (e.g. Roberts, 1995). T. saeva and T. gigantea were only recognized as separate species in 1975. Prior to that they were jointly known as ‘T. saeva’ or, earlier still, as ‘T. atrica’ (see Locket, 1975 and Oxford & Smith, 1987 for a history of the name changes))

Contents

Etymology:

Tegenaria - Latin ‘teges’, a mat; Latin ‘arium’, a place (referring to the sheet web); saeva - Latin ‘saevus’, cruel or savage; gigantea - Latin ‘giganteus’, of the giants, huge; duellica - Latin ‘duellicus’, warlike.

General:

These two species comprise the most frequently encountered ‘large house spiders’ in Britain. Their size, hairiness and habit of stopping in the middle of dashes across floors make them the bête noir of those suffering from arachnophobia, and even of seasoned arachnologists (Bristowe, 1958).


Description:

Tegenaria saeva and T. gigantea are identical in size and appearance and can only be separated reliably by the form of the male palp and of the female epigyne in mature individuals. Body lengths of females vary from 11 to 16 mm, and for males from 10 to 14 mm. The cephalothorax is dark brown with pale brown lateral and central bands. The abdomen is generally dark but with a lighter central stripe from which run a number of oblique lateral bands, forming a series of chevrons. The legs are dark brown and unbanded. In mature males the legs are about 1.5 times longer than those of females of the same body length.

Distribution and habitat:

FIGURE 1. Simplified distributions of Tegenaria saeva (red) and T. gigantea (green) in England and Wales. Orange represents the zone of overlap and, within it, the blue line shows where species are predicted to be at equal frequency. No spatial information is available for the Isle of Man (shown in black). Adapted from Croucher et al. (2007).

In southern and central England and Wales the species show largely non-overlapping distributions with T. gigantea occupying the east and Midlands of England, and T. saeva the west of England and Wales (see Figure 1). In a band running from mid-Dorset north along the Welsh/English border, the distributions overlap to some extent and here hybridisation occurs. By contrast, in northern England and Scotland, approximately north of an east-west line drawn along the North Wales coast, the species distributions overlap almost entirely and massive hybridisation is evident (Oxford & Smith, 1987; Oxford & Plowman, 1991; Croucher et al., 2007). The reasons for the clear species’ distributions in the south, but overlap in the north are unknown (Anderson et al. 2009). However, in mid-Dorset the distributions of the two species appear to have been stable for at least a century. It is known that large house spiders were very rare in the north in the 19th century and the first half of the 20th century. In approximately the 1960s both species seem to have rapidly moved northwards and in the process the east-west distribution pattern of southern and central England and Wales became obscured (Oxford, 2009).

So what might keep the species apart across most of England and Wales? One possibility is that after the last Ice Age when humans returned to Britain they brought large house spiders with them. T. saeva happened to colonised the west of England and T. gigantea the east. The species then slowly spread out from these foci, building up their population sizes as they expanded their ranges (Anderson et al. 2009). When they eventually met the spread stopped, possibly because of competition between them. Once the present distributions had been established a T. saeva transported into T gigantea territory, for example, would most likely hybridise and any offspring backcross to T. gigantea. The T. saeva genome would essentially be ‘hybridised away’, thus preserving the species’ distributions. There are molecular data supporting this suggestion (Croucher et al. 2004).

Tegenaria saeva outside its retreat

Both T. saeva and T. gigantea live within human dwellings (e.g. houses, garages and garden sheds) and outside in more natural habitats (e.g. earth banks, rabbit burrows, rock crevices and tree holes) throughout Britain. They spin large flat sheet webs (cobwebs) of non-sticky silk, with a tubular retreat in one corner. In undisturbed sites these webs have astonishing longevity and can be used by successive individuals of varying stages of development and even by other species, such as Tegenaria domestica, the ‘common house spider’ (Oxford, 2007).

General life history:

Large house spiders take two years to reach maturity. They emerge from the egg sac in late spring and grow to about half-size by the following winter, during which, in most habitats, growth ceases as the food supply dwindles. In spring growth is resumed, with males maturing in July/August and females in September/October. In early autumn males go in search of females, and it is this time of year when these species are most noticeable, running across carpets and falling into sinks and baths. A male finds a female close to maturation and guards her until she undergoes her final moult. Mating then takes place on the female’s web after preliminary bouts of palp-tapping and abdomen-bobbing by the male. Afterwards the male continues to co-habit with the female, mating repeatedly, until he eventually dies. The female overwinters with stored sperm and the next spring produces a succession of egg sacs, each containing c. 40 to 60 eggs. The number of egg sacs produced depends on food supply but it can be 10 or more and they are often ‘decorated’ with debris such as the remains of flies. Females usually die before the next winter.

House spiders in medicine:

Throughout history spiders have played a part in medicine. Pliny and Celsus recommended cobwebs for staunching the flow of blood from wounds, healing open sores and warding off inflammation (Parker & Harley, 1992). Eleazer Albin wrote in 1736 the following, ‘The clean web of the house spider, dip it in the spawn of frogs, beaten as you would the white of eggs, several times letting it dry on pewter and keep in a box close stopped from air’ (Hillyard, 1988). The term ‘house spider’ is rather generic but the sheet webs of various Tegenaria species would certainly have been tough enough, of a sufficient area and readily obtained. House spiders were also taken internally to combat fevers. Richard Mead, writing in the 1700s, gave the prescription, ‘Take a spider alive, cover it with the new soft crummy bread without bruising it; let the patient swallow it fasting. This is an effectual cure, but many people are set against it. It has been frequently given to people who did not know the contents and has had the desired effect’ (Hillyard, 1988).

References:

Anderson, B. J., Bai, Y., Thomas, C. D. & Oxford, G. S. (2009) Predicting range overlap in two closely related species of spiders. Insect Conser. Diver. 2: 135-141.

Bristowe, W. S. (1958) The World of Spiders. Collins New Naturalist, London. UK.


Croucher, P. J. P., Oxford, G. S. & Searle, J. B. (2004) Mitochondrial differentiation, introgression and phylogeny of species in the Tegenaria atrica group (Araneae, Agelenidae). Biol. J. Linn. Soc. 81: 79-89.

Croucher, P. J. P., Jones, R. M., Searle, J. B. & Oxford, G. S. (2007) Contrasting patterns of hybridization in large house spiders (Tegenaria atrica group, Agelenidae). Evolution, 61: 1622-1640.

Hillyard, P. (1988) The Book of the Spider. Hutchinson, London. UK.

Locket, G. H. (1975) The identity of Blackwall’s Tegenaria saeva (Araneae, Agelenidae). Bull. Br. arachnol. Soc., 3: 85-90.

Oxford, G. S. (2007) Multi-individual and multi-species use of a single sheet web. Newsl. Br. Arachnol. Soc., 108: 3-4.

Oxford, G. S. (2009) Historical distributions in Britain of two species of large house spiders, Tegenaria saeva and T. gigantea (Araneae, Agelenidae), and their evolutionary implications. Bull. Br. arachnol. Soc., 14: 297-302.

Oxford, G. S. & Plowman, A. (1991) Do large house spiders Tegenaria gigantea and T. saeva (Araneae, Agelenidae) hybridise in the wild? - A multivariate approach. Bull. Br. arachnol. Soc., 8: 293-296.

Oxford, G. S. & Smith, C. J. (1987) The distribution of Tegenaria gigantea Chamberlain and Ivie, 1935 and T. saeva Blackwall, 1844 (Araneae, Agelenidae) in Yorkshire. Bull. Br. arachnol. Soc., 7: 123-127.

Parker, J. & Harley, B. (1992) Martin Lister’s English Spiders 1678. Harley Books, Colchester. UK.

Roberts, M. J. (1995) Collins Field Guide to Spiders of Britain and Northern Europe. Harper Collins, London, UK.


Geoff Oxford
February 2010


Link to the Spider Recording Scheme's page on Tegenaria saeva: http://srs.britishspiders.org.uk/portal.php/p/Summary/s/Tegenaria+saeva

Link to the Spider Recording Scheme's page on Tegenaria gigantea: http://srs.britishspiders.org.uk/portal.php/p/Summary/s/Tegenaria+gigantea

External Links

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

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