Frost, Photography and a Frozen Furca

01st December 2012

Even when there's frost on the ground, opportunities are still available for insect photography. In fact, new opportunities are presented, and I was out early during the recent frosts looking for insects trapped in the cold. I had some reasonable success but was particularly pleased with the aphid shot (top left). This is a composite of nine images combined with Zerene Stacker software. The benefit of the cold is that (generally), insects are immobile and this is particularly useful when "stacking" is planned. No antennae waving about!

Also with the cold spell, I've been seeing quite a few dead springtails. Anyone reading my Blog or following me on Twitter recently, will know that I've become a bit obsessed with learning more about them! The dead globular springtail (second image down) has the benefit of revealing the springtail's secret defence mechanism; the furca (or furcula). Normally held in place under the abdomen (with another special structure), this two-pronged organ once released, flips the springtail into the air. Different species and groups within the springtails (Collembola), have furca of varying sizes. Some springtails that live deeper in the soil, have none at all.

Not only is the furca a fascinating feature of the Collembola; there is also the collophore (or ventral tube). This emerges from underneath the 1st abdominal segment and has several functions; thought to include osmoregulation, adhesion and water absorption. Normally just a short "stump", the springtail can extrude two long worm-like tubes (eversible vesicles) from the collophore and these can be seen in the image third from the top. These vesicles have been placed in the fluid film on a fallen leaf, to absorb moisture. It wasn't until I looked at the images on my computer that I realised that I had captured this. It's not witnessed that often and only occasionally photographed. The vesicles are also used to help discharge waste products (urine) onto the water surface film; where some additional ion-exchange takes place.

In my garden and surrounding areas; Dicyrtomina springtails are the ones I am seeing most commonly. There are three UK species; Dicyrtomina minuta, Dicyrtomina ornata and Dicyrtomina saundersi. Once believed to be colour varaitions of the same species, it's now generally thought that they are all different. In the final image (bottom left), you can see two of these species. The larger is Dicyrtomina saundersi, showing typical green and brown colouration and an area of pigmentation at the rear of the abdomen resembling a multi-barred cross. Dicyrtomina minuta is the smaller and this is generally yellow, with a dark brownish/blue area of pigmentation at the rear of the abdomen. Despite the name, Dicyrtomina minuta can grow as large as the other Dicyrtomina species. All the ones I have seen though, have been somewhat smaller.

Well, a reasonable successful week of insect photography, despite the weather. I'm now waiting for some more frost!

[Click on images for a larger version]

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