Massive rainbow worm emergence

I woke up early this morning and went for a walk around the park. It was cold and it had rained a lot in the night. I had to watch my step as there were hundreds of blue-grey worms, Octolasion cyaneum, on the pavements and ground. This is a very colourful and common earthworm species, easily recognised by its yellow tail end and its orange clitellum (the central raised band) when adult. They are sluggish, live in topsoil and commonly emerge in large numbers after rain. Some individuals were the largest I've ever seen, over 26 cm! (bottom shot), although around 15 cm was much more common. I was surprised there weren't more blackbirds and thrushes feeding on this worm bonanza! Why do they come up in the rain? Reproduction can be ruled out as this species is parthenogenetic, that is, they can reproduce on their own, producing genetically identical offspring. Populations have little diversity and are made or clonal lines. Adult worms lay cocoons in the soil that contain singletons or twins.

More information
Lowe, Christopher N., and Kevin R. Butt. Life cycle traits of the parthenogenetic earthworm Octolasion cyaneum (Savigny, 1826). European Journal of Soil Biology 44.5 (2008): 541-544.

Looooong legs!

 This Dicranopalpus ramosus harvestman posed in the flattened, all legs stretched posture typical of the species. There were lots of them sitting on headstones in my local cemetery today. When disturbed, they walk as a 'normal' harvestman', but soon after sit and stretch their legs again.

A close up of the individual above, a female.

A leggy centipede

I was pleased to come across this centipede Stigmatogaster subterranea in leaf litter while gardening.  I counted 79 leg segments - with a pair of legs each -, a normal number for this species, which can easily be the leggiest beast in the garden. Winter has been very long this year: no bees or butterflies, or even droneflies, and very few active invertebrates around, so BugBlog remains dormant, but hopefully not for long.

Centipede on a walkabout

It is long, I counted 76 pairs of legs! My young daughter spotted this centipede, Stigmatogaster subterranea, walking on a stone wall out in the open. This is the first time I see this behaviour in this otherwise soil and leaf-litter living centipede. When disturbed, it had no trouble walking backwards, which had me puzzled for a bit, as I confused the tail and the head end!

The centipede lifted its head as if sniffing...

 ...and finally disappeared in the leaf litter.

An impressive slug

A showery day, I come across this enormous Arion slug crossing the garden path. It must be close to 15 cm. Identification to species level is difficult to impossible as they are distinguishable by examination of internal genitalia characters - or molecular genetic analysis, and hybrids are common. British large Arion slugs are made of several species complexes, Arion ater/rufus A. lusitanicus and A. flagellus. Both groups are very polymorphic slugs, from almost white to black, including all shades of brown yellow red and orange. I have never found the the black morph in the garden, but a good representation of the others abound. The polymorphism of these slugs in the U.K., not only in colour, but also in genital characters, might stem from common hybridisation between several subspecies that colonised the British Isles from Europe, postglacially but also in more recent human introductions. Distribution changes might also come about due to expansions as a result of climate change. In addition, the slugs - except for A. flagellus - are able to self-fertilise and form relatively homogeneous populations, which might give the impression of being a separate species.

 Arion slugs had deep tubercles on their backs, and no keel. At the end tip is the mucus gland, producing an extremely sticky mucus. Unlike the yellow slug, which is strictly nocturnal, Arion slugs are active all around the day, provided that it is damp. When disturbed they show a characteristic behaviour: they contract their bodies into an almost round shape and retract their tentacles inside their mantle. Inspired by a post in Myrmecos, I set the photo vertically. I had to use a white plate - instead of bowl - and allow the slug to relax and start to crawl out. 

A very yellow specimen

A disturbed Arion

A selection of colours found in the garden

The black morph of Arion sp.

References

Noble, L. R. Jones, C. S. (1996). A molecular and ecological investigation of the large arionid slugs of North-West Europe: the potential for new pests The ecology of agricultural pests: biochemical approaches Ed. William O. C. Symondson, Systematics Association, special volume. Clarendon Press., 53, 93-132
Evans, N. (1986). An investigation of the status of the terrestrial slugs Arion ater ater (L.) and Arion ater rufus (L.) (Mollusca, Gastropoda, Pulmonata) in Britain Zoologica Scripta, 15 (4), 313-322 DOI: 10.1111/j.1463-6409.1986.tb00232.x
UPDATE 30/08/11: reference added and Arion ater in a photo caption changed to Arion sp.