I'm not sure what species (Arcitalitrus sylvestris or dorrieni) they
are, but 'landhoppers' appear to be more prevalent and spreading.
They are significantly larger than 'springtails' being upwards of 1cm.
long. I understand they are alien to the UK, but became established
in milder coastal regions and have spread steadily outside these
ranges. To all intents and purposes, they appear to be the land
equivalent of the freshwater shrimp and feed on decaying plant matter
and detritus. They do no harm to living plants, although it can be a
bit surprising to shift a pot or a pile of wet leaves and find
hundreds of them frantically hopping about in order to escape the
light. I first noticed them in my garden several years ago and
mentioned it here on URG at the time.