(Left: Unknown katiannidae, Sheffield botanic gardens)
The invaders in question are springtails (Collembola) and they’re only alien from a European perspective, but genuinely there is still a fair chance of collecting a prettily coloured little springer — which turns out to be scientifically undescribed — from your back garden.
The UK has a longer history of springtail collection than almost anywhere (John Lubbock was publishing records of springtail collections in the 1860s), and we have been generating distribution data almost continually since, so one would expect the UK springtail fauna to be well studied by now. It is true that collections of springtails from many British habitats (eg upland bogs, strandline, tree bark and caves) reveal lists of names that seem to have changed little for at least a century. (The possible effects of climate change on this are a blog in themselves). Before his untimely death Steve Hopkin wrote the FSC key to this group, which will usually give sensible names for springtails collected in these “pristine” habitats (though early instars remain a challenge).
However, when one collects in urban gardens or peri-urban settings it is routine to turn up springtails that simply won’t key down properly in the FSC key, or indeed any of the standard European texts. The majority of these oddities are in the Symphypleona, the jumpy surface-active forms with fused body segments and a distinctive body shape that gives them – in my subjective eyes – a slightly extra-terrestrial look. The most commonly photographed one is Dicyrtomina saundersi.
Entomologists have found non-native springtails in the UK many times before, but almost invariably in warm artificial habitats. The great Richard Bagnall found a pretty little sminthurid Sphyrotheca multifasciata in hot houses in two botanic gardens in the 1920s, and the closure of one worm bed at Rothamsted removed the Philippine springtail Yuukianura aphoruroides from the British Fauna.
(Photo from Collembola.org)
In about 2007, photographs started to turn up on internet macro-photography pages of attractively patterned symphypleona that simply didn’t fit anything in the FSC key. A lovely example is here if you can log into flickr.
This creature was thought to be Sphyrotheca multifasciata for a short while, but the chaetotaxy isn’t right and the color pattern is unlike what has been published. Having consulted Dr. Penny Greenslade (CSIRO) – a world expert on the group - it is not clear even what genus this belongs in. Apparently the same species has been found in several places in the UK including Manchester, and was one of the commonest Collembola collected by myself from the woods near Bodmin in 2011.
Paul Ardron found multiple non-native springtails in Sheffield Botanic gardens and The Lost Gardens of Heligan, publishing photographs of 12 taxa, five of which could not (and still cannot) be named, in a paper called Aliens in Inner Space, which can be found on page 10 of this document.
The identifiable species included at least three from the southern hemisphere, verified by Greenslade and not previously known in the UK: Katianna australis, K. schoetti, and (from a different family) Calvatomina superba.
During vacuum collection from the RHS Wisley experiment “Plants for Bugs”, one of the commoner leaf-surface springtails was again this Australian katiannid Katianna schoetti.
Stephanie Bird’s PhD involved monitoring the Collembola in these Plants for Bugs plots, and (by luck) she seems to have observed a wave of colonisation in action. The second year (2013) of monitoring all her plots (including local heathland) acquired good numbers of Sminthurinus reticulatus, which had not been seen there before. This colour-pattern species can easily be seen under a dissecting microscope to have a ladder like pattern up its back, and was first found in the UK by Keith Brocklehurst in 2007.
It went from unknown to the commonest springtail in my college leaf litter in 2012, and also appeared in ancient woodland on Bookham common about the same time, and seems to have displaced the two native colour forms of Sminthurinus aureus.
Just last week (Feb 2014) Ed Phillips emailed photos of this same springtail – it was the dominant symphypleonan in his Warwickshire churchyard. It will be fascinating to follow its colonisation, which I presume to be northwards associated with our increasingly mild (if wet!) climate.
I have sent several of these unfamiliar springtails for DNA barcoding – results are eagerly awaited.
Finally, a story that probably fits here but remains a puzzle. One of the commonest and biggest springtails in the UK is Tomocerus vulgaris:
It has a mucro (tooth on jumping organ) with about five small teeth along its middle. Except that a few places in the SE are turning up a Tomocerus that otherwise fits but has “red lipstick” (red pigment on its labrum) and only has one medial tooth. This should be either the Catalan species (but isn’t like it in any other way) or T. minutus of Scottish mountains (but certainly isn’t), or a new species. Its DNA was sequenced and gave a 95% match to T. vulgaris – close enough to write it off as a mutant, or far enough away to call it a new species? More work (and research funding) is needed.