Giant house spiders

by George Wykes

Photo by Hayley Simms on Unsplash

Welcome to our feature on Giant House Spiders.

We hope you have been enjoying our focus on these most misunderstood carnivores throughout Autumn. Here we look at some of the larger spiders you may come across if you are lucky as they search for food and mates. Spiders are highly important to ecosystems as both predators and prey. Next time you catch a glimpse of one be sure to marvel at these perfect carnivores that evolution has moulded so well into filling such important niches on our planet over millions of years. As always, we hope you enjoy the article!

The big debate:

Is the giant house spider one species or three?

It is generally accepted now that there are three species of giant house spider residing in the U.K. This however, is a debate that over the course of the last decade has twisted and turned with arguments and counter arguments resulting in a fascinating insight into the complexities of assigning and differentiating species. 

Timeline detailing the key moments of the debate.

Pre 2013: It was widely accepted that three species of giant house spider existed, however at the time the genus name was previously Tegenaria with species listed as Tegenaria duellica, Tegenaria saeva and Tegenaria atrica.

2013: A study by Bolzern, Burckhardt & Hänggi acknowledged that while there are variations within the spiders they studied, they refute the idea of individual species and instead claim that there should only be one accepted species along with being reclassified into the genus Eratigena. This recommendation was based on two factors, firstly they were unable to find differences between species mitochondrial DNA sequences and secondly, they felt there was a continuum of the genital morphologies in their study animals.

 

2014: These opinions are countered however by Oxford and Smith who in their 2014 study argued that previous research did not factor into account that E. atrica can be distinguished from E. duellica and E.saeva and that E. duellica and E.saeva are distinguishable through studying their epigynes (the external genital structure of female spiders a feature commonly used to distinguish species) and pedipalps also know as palps. Males and females both possess palps however sexually mature males will have a palpal bulb at the end of these appendages. This is used to transport sperm during mating. 

While the  species changes were hotly contested, the change in genus however was more readily accepted by experts and went onto remain as Eratigena.

2018: The World Spider Catalogue accepts the changes suggested and puts the three species into a single species (E. atrica). 

2018: Oxford and Bolzern again refute this change and through new research again site morphological differences between species as a reason to reclassify three separate species. 

April 2020: E. duellica and E. saeva are reclassified as a separate species of giant house spider on the World Spider Catalogue. 

Conclusion of the debate as it stands.

Records of these species can be hard to accurately identify, as hybridisation can occur, and it appears the ongoing debate has not yet been closed. 

A focus on Eratigena atrica

July marks the first emergence of male E. Atrica and this is quickly followed by a steady increase in abundance before reaching its peak in August. This is then followed by a rapid decline as males stop feeding. Linked to this is an observation by Stoltz et al. 2007 who proposed female populations reach their greatest numbers when male population numbers decline. It has been suggested this could be due to females only mating once and males consciously selecting virgin females to mate with. It may also be that first sperm precedence is present in the mating behaviour of this species in where the sperm of the first male to mate is strongly favoured above all others. Spiderlings emerge from their egg sacs in the early stages of Autumn having spent just a few weeks within them. An interesting trait of the species is that they are subsocial, with spiderlings staying together for up to a month. The diet of E. atrica is highly varied, with arthropod prey consisting of Isopoda (an order of crustaceans including woodlice), Aranea (spiders), Lepidoptera (moths and butterflies) and Diptera (true flys).

Differences in distribution and historical expansion of ranges. 

E.atrica is suspected to have become established in the U.K during Victorian times. Despite this and the fact it is considered common on the continent and the Republic of Ireland, it had long been documented that E.atrica had consistently struggled to establish self – sustaining populations. This changed in 2009 after research conducted by Burnopfield, situated in County Durham revealed the first established population in large numbers and further research showed a core range of 400 km2 and an overall range of 710km2 which includes Tyne and Wear and south-east Northumberland.  What’s most interesting about this is when closely related species E. saeva and E.duellica began to expand their range in the 1960’s, it is theorised that priority effects (the result of the order of species arriving at  a habitat patch and resulting subsequent interactions) may have protected E. atrica from suffering from intense competition. Indeed, throughout the 400km2 range observed by the researchers, both E. saeva and E.duellica were largely observed to be uncommon or even absent completely.

 

In contrast to a relative scarcity in the North of the UK, with the exception of the sporadic translocations, E. saeva is reported to be the only present established species in south western counties and Wales. E. duellica on the other hand, has large populations in the English Midlands and the east while a smaller one exists in North Wales. Interestingly, despite the differences in ranges, E.duellica and E.saeva do meet in a restricted range from mid Dorset and continues north along the Welsh border. It’s suggested through prior research that this co-existence has gone on for a minimum of one hundred years. Furthermore, in the north of England both species can also be found in the same range or overlapping areas a term known scientifically as sympatry. Historical evidence has been used by Oxford (2009) to suggest that this advance towards northern regions took place during the mid-1960s.

So how did these three species arrive in the U.K and the Republic or Ireland in the first place? Historically these species have colonised many parts of the world through accidental importation through transportation by humans and it is thought likely that this is how their introductions began in this case too. However they arrived, intentional or not, it seems likely that they are here to stay and we should be grateful for that as spiders are tremendously important in controlling populations of pest species . For more on this and why we should learn to love spiders, why not follow the link to a fantastic article written by Sasha Remnant here.

If you have enjoyed our articles on our website why not follow us on Instagram, Twitter and FaceBook @PlanetCarnivore where we will be continuing to highlight the incredible diversity of spiders around the world and especially in the U.K. 

 

 

 

 

 

 

References 

Oxford, Geoff S., and Angelo Bolzern. "Molecules v. Morphology—isEratigena Atrica(Araneae: Agelenidae) One Species or Three?" Arachnology 17, no. 7 (2018): 337-57. doi:10.13156/arac.2017.17.7.337.

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