Seasonal Nature Trackers: Fat Spider Fortnight

Close-up of spider on web

A European garden spider (Araneus diadematus) showing its distinctive white cross © Vojtech Myslivec/

At a glance

Record sightings of spiders, with a focus on 11 species

Type of activity: Outdoors/indoors

Who can take part? Everyone

When? 6-19 September 2021. Project finished for 2021. Will be repeated autumn 2022.

How long will it take? A few minutes per spider

Project results

This project has now finished for 2021. Many thanks to everyone who contributed.

  • Over 670 people took part, making over 1250 observations.
  • All 11 target species were observed.
  • At least 10 new geographic ranges were established - new areas where a species has never been recorded before.

You can view all the observations and a map of where they were recorded on the iNaturalist Fat Spider Fortnight project page.

Look out for another Fat Spider Fortnight in the autumn of 2022.

What your observations found

Spider expert Tylan Berry comments on the results:

'Looking at initial findings, the project has captured some excellent and important data on the distribution and abundance of some species.

'It is of no surprise that the European garden spider (Araneus diadematus) was the most seen species, being recorded eight times more than any other during the fortnight. This is a great indication of how gardens are an important habitat for this well known and much loved spider.

'Perhaps most encouraging was that the project appears to have generated at least ten range extensions across the species list - this would be where a species was observed in a 10km square (hectad) where there are no current records held for the species.

'Data such as this is important for species that appear to be expanding their range, which the project has captured fantastically well for the green mesh weaver (Nigma walckenaeri). This spider was known to be a scarce in the past, being only found in the Thames corridor, but has steadily increased its range over the last few decades.

'The Fat Spider Fortnight project has uncovered at least five separate range extensions for this species, and what looks to be records to a new region of the UK!'

What we did in this project

Each September we invite people to join a spider-spotting team to build our understanding of how their populations are faring in the UK.

Autumn is an excellent time to go looking for spiders, as it's mating season for many species. Inside, you'll often spot male house spiders as they go searching for females. While out in the garden, female orb weavers grow fat as their abdomens swell with eggs.

There are over 670 species of spider living in the UK and they are an important part of our ecosystem. But our understanding of their distribution around the country, and how they are responding to ecological changes, is patchy.

By increasing the number and geographical range of observations made to biological recording schemes, we can build a better picture of how spiders are faring.

As part of our Urban Nature Project, we are particularly keen to improve our knowledge of spiders in towns and cities. Having a better baseline of spider distribution means that we can monitor any changes that may happen as biodiversity comes under extra pressure from a growing human population.

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How to take part

For Fat Spider Fortnight we're asking you to spend a couple of minutes looking for spiders in your house or garden. Pay attention to quiet corners, cracks and hard surfaces where spiders might shelter or build their web.

Once you've found a spider, make your observation by taking a picture on your phone and uploading it using the free iNaturalist app.

There are 11 spider species that we are particulary interested in. See the list below for more on these.

  1. Download. You can download the free iNaturalist app onto your smartphone, either from the Google Play store for Android phones or the Apple App store for iPhones.
    If you’d rather use your camera and a browser, then you can sign up on the iNaturalistUK website, then upload your photos later.
  2. Register. On the iNaturalist app, create an account and join the NHM Fat Spider Fortnight project so that your results can count and that you can see other people's entries.
  3. See it. Find a spider between 6-19 Sept 2021. Please see the list below for the 11 spider species we are particularly interested in.
  4. Snap it. Take a picture of the spider you've found. 
  5. Record it. Record what you find by uploading a picture onto the iNaturalist app or at iNaturalistUK.
  6. Log your location. Please note: it's important that you log the location of where you saw the spider. If you take the photo through the iNaturalist app, please ensure that your phone location information is turned on.
    If you upload a picture later onto the app from your phone's photo gallery, or upload via a web browser, then you may have to add the location manually.

What will happen to my data?

Observations added to iNaturalistUK may be shared to the National Biodiversity Network Trust’s NBN Atlas, which amalgamates and shares biodiversity data for the whole of the UK. Any iNaturalistUK observations that reach research grade will be shared with the Global Biodiversity Information Facility (GBIF). This enables them to be analysed and researched widely, to better understand the UK's rich biodiversity.

Spider expert Tylan Berry is an Area Organiser for the Spider Recording Scheme, and is working with us on Fat Spider Fortnight. He will check the photos you submit, adding the data to the individual species accounts in the British Arachnological Society's Spider Recording Scheme database. 

Why spiders are important

Spiders are some of the most abundant predators on the planet and play a vital role in ecosystems.

'They help keep the populations of many other creatures in check,' Tylan says. 'And with nearly 50,000 species worldwide it is a hugely diverse and fascinating group, each species having its own niche and nuances in behavioural characteristics. This gives each species an almost unique personality.

'Another great thing about recording spiders in Britain is that they are always around in some form or another at all times of the year and can be located regardless of the weather!'

Spider species to look out for and record

There are 11 species of spider that we'd you like to look out for and record on the iNaturalist app or at iNaturalistUK. Each spider has a link to their page on the website of the British Arachnological Society's Spider Recording Scheme, where you can find more information on their regional distribution and lifestyle.

European garden spider - Araneus diadematus

Often seen in autumnal gardens where the females sit in the middle of their large orb webs. Also called the cross spider due to the distinctive white cross pattern on the abdomen. Found everywhere in the UK other than high moorland and mountains.
(Image © Daniel Blyton)

Walnut orb weaver - Nuctenea umbratica

A large orb weaver with a dark, flattened body which allows them to hide in crevices under bark on trees. They are commonly seen throughout the UK in gardens where the spider hides in the gaps between fence panels.
(Image © Roger Harris)

Noble false widow - Steatoda nobilis

A large spider that is now a regular sight in gardens, on walls and fences, where it creates a large sheet web which the spider runs underneath, usually hiding away during the day in a crack or crevice. They are widespread throughout the UK with the highest population densities being found in the south.
(Image © Daniel Blyton)

Daddy long legs spider/cellar spider - Pholcus phalangioides

A familiar sight inside houses and outbuildings, this long-legged species is widespread throughout the UK, though commoner in the south.
(Image © Stuart MacKenzie)

Nursery web spider - Pisaura mirabilis

A common spider of grasslands that is regularly found at ground level in grassy gardens. The females build a silk tent in low vegetation where she guards the egg sac and the young when they emerge. The long legs, pointed oval abdomen and pale flanks to the side of the head area make this spider quite distinctive.
(Image © Sue Jones)

Flower crab spider - Misumena vatia

A colourful crab spider that is found on flowers in most habitats and is regularly found in gardens. The females are one of three colours: white, white with cream sides to the abdomen or bright yellow.
(Image © Rev Vince Napper)

Green mesh weaver - Nigma walckenaeri

A small green spider that spins a mesh web on the upper side of leaves in hedges and bushes, quite often ivy, holly and lilac. The spider has been considered scarce in the past, being restricted to the southeast and the Thames corridor, but has shown signs of significant expansion in recent decades.
(Image © Daniel Bell)

Toothed weaver - Textrix denticulata

A relative of the well-known giant house spiders, this little spider creates its small sheet web on rocky terrain or stone walls. It’s widespread - commoner in the north but apparently rare or absent in most of the southeast. It resembles a wolf spider but can be identified by the long spinnerets at the end of the abdomen.
(Image © Derek Mayes)

Tube web spider - Segestria florentina

One of Britain’s largest spiders with females having a body length of over 20mm excluding the legs. They create tube webs in holes in walls and fences, commonly around human habitation. Originally restricted to ports in the south, it has expanded its range considerably in recent years and continues to spread northwards.
(Image © Link)

Spitting spider - Scytodes thoracica

This small spider is confined to houses and outbuildings where it attacks prey by squirting a sticky gum at it. It is widespread in the south, but not commonly seen, and is apparently rare in the north. The domed carapace is rather unique to this species in the UK.
(Image © Lindsay Murrell)

False wolf spider - Zoropsis spinimana

A relatively new arrival to Britain, this large spider was originally found in houses in the London area a decade ago. Whilst it is still restricted to the inside of buildings, it is beginning to be found much further afield across the country.
(Image © John Jackson)

About the British Arachnological Society

The British Arachnological Society is Britain’s only charity dedicated exclusively to spiders and their relatives, advancing the wider understanding and appreciation of arachnids and promoting their conservation.


We thank all funders to the Urban Nature Project campaign so far, including those who wish to remain anonymous, for their generous support. We recognise the following funders for their exceptional contributions to the campaign:

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