According to Steve Hopkin (a UK Collembola expert) on his website (https://tinyurl.com/344w6nh4), there are 23 species of 'littoral' (meaning intertidal/seashore) springtails found in the UK. These 23 springtails are split across two orders (Poduromorpha and Entomobryomorpha) and five families (Hypogastruridae, Neanuridae and Onychiuridae within Poduromorpha; Entomobryidae and Isotomidae within Entomobryomorpha).

As far as I can tell, in most cases it seems to be impossible to ID any of these 23 springtails down to species from photographs and/or a description of habitat or behaviour alone. Rather, as per Steve Hopkin's website (https://tinyurl.com/344w6nh4), it is only with a view of microscopic features that identifications can be made. That being said, one can certainly go down to order or family in some cases, particularly if close-up photos of individuals are provided.

Identifying to order:

According to Dallimore and Shaw's (2013) 'Illustrated key to the families of British Springtails (Collembola)', Poduromorpha and Entomobryomorpha can be distinguished from one another by the state of the first thoracic segment. Both Poduromorpha and Entomobryomorpha technically have three thoracic segments, however in Entomobryomorpha the first thoracic segment is greatly reduced dorsally, such that it almost appears as if the springtail has a 'neck'. Poduromorpha, in contrast, have a visible first thoracic segment. For a clear example, compare https://www.inaturalist.org/observations/75409414 with https://www.inaturalist.org/observations/194018768.

Identifying to family:

Within Poduromorpha (12 littoral species):

• As far as I am aware, littoral Hypogastruridae cannot be reliably distinguished from littoral Neanuridae from photographs alone. (see this separate journal post for more information: https://tinyurl.com/26ycb3bx)
• It is likely that any unpigmented (i.e. white) and blind littoral Poduromorpha springtail is one of the three littoral species within Onychiuridae (Protaphorura macfadyeni, Thalassaphorura debilis or Thalassaphorura halophila), however this call cannot be made with 100% certainty given that the colouration of some other Poduromorpha springtails in Hypogastruridae and Neanuridae is not known for certain given that photos of these species are lacking (As per https://www.collembola.org/ 5 of the 9 non-Onychiuridae littoral springtails lack photos).

Within Entomobryomorpha (11 littoral species):

• Entomobryidae can be identified to family if it is clear that the 4th abdominal segment is notably longer than the other abdominal segments.
• Isotomidae can be identified to family is it is clear that all the abdominal segments are of similar length.
• I imagine that it is possible that ID beyond family here too, I simply lack the knowledge personally.

Congregating behaviour:

I am yet to see any definitive evidence that the 'congregating' behaviour exhibited by some littoral springtails (e.g. see here: https://inaturalist.org/observations/127831994) is a unique feature of a distinct subset of the 23 littoral species. Given that many of the 23 littoral species lack everything besides a basic description, and some do not even have photos on the global databse (https://www.collembola.org/), I strongly suggest that using this congregating feature as a determinant for an ID is inappropriate.

Posted on April 5, 2024 09:40 AM by josscarr