A garden springtail survey
15th February 2017
In: February 2017
In 2009, Dr Paul Ardron published an article describing a number of “alien” springtail species that he had discovered at various UK locations including Sheffield Botanical Gardens and the Lost Gardens of Heligan in Cornwall. Some were new to the UK, some new to science. It was speculated that they may have been introduced on imported plants. Since then, some of the species have been reported from various locations around the UK; this year I found one of them (Katiannidae Genus nov.1 species nov.) in our Staffordshire garden. The rather unusual name denotes the fact this member of the Katiannidae is a previously-undescribed species in a previously-undescribed genus.
I’m a keen photographer of insects and other invertebrates and the colder, wetter days during autumn and winter provide a good opportunity to photographs springtails and other members of the soil meso-fauna. It keeps me occupied until the mining-bee species start emerging again in early spring. Having my own garden colony is great because I can check them every day with minimum effort. Dr Frans Janssens from the University of Antwerp, asked me if I would help him with a survey; to attempt to document (via photographs); all the male and female instars of the species. I was happy to assist.
Springtails are difficult to photograph because of their small size. In fact, this makes them difficult to see with the naked eye and most people never notice them, or even know of their existence. Springtails though, are extremely common and widespread. This species varies from less than 0.4 mm in early instars up to about 1.5 mm in adult females. Males are generally a little smaller. It’s thought that both sexes have around five juvenile instars and five adult instars. All instars look similar. The springtails just get a little bigger after each moult and (generally), develop darker pigmentation.
I found the first individual on 2nd November 2016 and have been photographing them regularly since. I’ve been posting images on my Flickr Photostream since; usually on the day they were photographed. To assist in determining the degree of maturity of individual springtails, I’ve created a ruler overlay which allows them to be measured to within 0.1 mm.
It’s been a pleasure seeking-out these tiny creatures; not only for the challenge, but because (in my eyes anyway) they are rather beautiful. The image below shows two mature adult females in different colour forms:
Now, this difference in colouration is interesting. It had been assumed (based on some early observations) that this was a species that exhibited marked sexual dimorphism. This means that (apart from the differences in their sexual apparatus), sexes looked very different. This is not uncommon in the world of invertebrates. It was thought that red-backed individuals were male and those without a red back were female. I’ve shown that this is not the case. How did I know they were females? Well, in the Katiannidae, females have two sub-anal appendages that are just visible when the springtail is viewed from the side. Here’s two close-up images:
I have found males too (mostly at another colony in a Staffordshire village churchyard). They have an enlarged genital papilla that is even more difficult to see! The males have generally, had an overall orangey/red colouration, somewhere halfway between the extremes of the female colour forms. The one below is one of the darker individuals that I've photographed.
Once it had become apparent that the red and non-red individuals could both be females, it raised another question. The very different appearances were not related to sexual dimorphism, so could this species have two distinct colour forms. Even; could they be different sub-species/species? At the time of writing, contact has been made with Dr Peter Shaw who is the UK recorder for Collembola (springtails) at Roehampton University’s Centre for Research in Ecology. He has agreed to arrange for some detailed testing to be undertaken.
Currently, Frans Janssens is proposing that two colour forms exist; Group 1, where in adults, abd.6 (the final abdominal segment) is non-pigmented, and Group 2, where in adults, abd.6 is pigmented. I shall update this article in the future, should additional information become available.
To complete this blog post, here’s a series of images showing how the instars (a random selection of immature, mature, male, female, light forms, dark forms) vary as they mature.
If you have a hand-lens or magnifying glass, why not have a look for springtails in your own garden? They can often be found under fallen leaves and bark, on low vegetation, feeding on algae on old water vats, in compost bins etc.. They are fascinating little creatures!
For more information on springtails, visit Frans' comprehensive Collembola of the World website.