Saturday 13 June 2015

A Slug day

As predicted, it rained all night and most of the morning. In the afternoon, the rain turned to drizzle and eventually stopped. This was an ideal day slugs, so my youngest daughter and I went to the wildlife garden to try and see some. Slugs don't have many fans. Many gardeners detest them and fight the slug wars with any means available. Out of the 40+ British species, many of them introduced, some are indeed serious agricultural pests specialising on feeding on living plant tissue. Slugs as a group, however, are ecologically very diverse and most species cause little or no damage feeding on algae, decaying plants, lichens, carrion, or fungi. A few species are earthworm predators. Slugs are not a natural group, they are a mixed bag of snails which have lost their shells: British slugs are the result of four different evolutionary shell loses, each group being more closely related to a different snail family, but more on that on a future post.
 Slugs were plentiful in the garden today and gave a good idea of the diversity of the British fauna. A nice feature of slugs is that they can be easily collected by hand - provided you don't mind getting covered in their mucus - and they are best identified live, so no collecting is necessary (except for some species where dissection is necessary for identification). I tried to get photos of the right side of the slug, with shows the breathing pore and other diagnostic characters, and used the Slugs of Britain and Ireland FSC guide by Ben Rowson and colleagues to identify them. I am no expert, and if you see any misidentification, I will be grateful if you let me know.
 We first came across some large Arion slugs (above photo). These are often active and out and about during the day. The one on the top shot was feeding quite high up on an angelica plant. When disturbed (e.g. poked with a finger), these slugs make a semispherical hump. The first one we came across, a very dark one, started rocking from side to side, a dancing slug was a good start! Only a couple of very variable species, Arion ater and Arion rufus will show this rocking response. Despite its dark colour, this one appears to fits better with Arion rufus, which has a bright orange foot fringe, but Arion often hybridise and species identification is tricky, especially in disturbed habitats.

This was another large Arion, which wasn't as keen to dance:
An Arion adopting its humped defence position.

We found the next slug, the Iberian Threeband Slug, Ambigolimax valentinus, inside an upturned plastic pot, which is fitting as this species is thought to have been introduced initially to greenhouses, but now it is readily found outdoors.
Ambigolimax valentinus

And now to our 'kitchen slug': the Green Cellar Slug, Limacus maculatus. A large, strictly nocturnal species able to squeeze through the tiniest cracks. If you go out into your garden at night, you are likely to see this slug in large numbers. They will often feed on other dead slugs or snails that had the misfortune of being squished on paths during the day. The ones inside our house will feed on cat food if there is any left. This was found together with others under an upturned large plastic tray.

Limacus maculatus
We lifted a few logs and there I found one of my favourite slugs, the Worm Slug, Boettgerilla pallens. I've never seen it in my garden, but it is common in the Wildlife Garden. It is an introduced species first detected in the UK in 1972, when it was already widespread. It was first described from mountain forests in the Caucasus and since then it has spread to western Europe. It is a mainly detritivorous slug, long and thin when moving, reminiscent of a worm. It lives underground, down to 60 cm deep, and moves through earthworm burrows.
The Worm Slug on the log where we found it.

Worm slug on the white bowl.
I got to Deroceras invadens/panormitanum for the next two slugs. Although they look quite different, they look like they have a hump and a truncated tail.

The last one is also a Deroceras, but the tail end is not as truncated, so I got to Deroceras reticulatum.

Deroceras reticulatum

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