Spiders, Harvestmen, Scorpions, Pseudoscorpions and Ticks
Printed
British Spiders A field Guide by Lawrence Bee, Geoff Oxford & Helen Smith (Princeton Wild Guides, 2nd edition 2020)
Keys to the Families of British Spiders by LM Jones-Walters (FSC Aidgap, 1989)
Spiders of Britain & Northern Europe by Michael J Roberts (Collins 2001)
House and Garden Spiders by L Bee & R Lewington (FSC WildID fold-out guide 2002)
A Harvestmen of the British Isles by Paul Richards (FSC fold-out guide 2022)
Illustrated Key to the British False Scorpions (Pseudoscorpions) by G. Legg & F. Farr-Cox (FSC fold-out guide 2016)
Websites
British Arachnological Society Is the membership organisation for study of spiders and harvestmen. Their website has free factsheets and other useful guidance about identifying and studying arachnids.
Google Lens: Go to google.com and there is a camera icon at the right of the search bar. Click on this, and you can drag and drop any image and it will do its best to identify it – so can be used for any flora and fauna, vertebrates and invertebrates etc. (as well as buildings, landscapes – anything, in fact.) Worth a look, but treat identifications with caution!
Apps