Tuesday, July 13, 2010

"And safe and sound beneath a rock shelf"

from "Arion" by Seamus Heaney

The line above refers above to the legend of the poet Arion and the dolphin. The story goes that on being thrown from the ship he was a passenger on, the Greek poet Arion was rescued by a dolphin, the creature being attracted by his singing. The dolphin carried him ashore, saving him from drowning.

It could also refer to the family of animals which now bear his name, the Arionidae. These are a family of robust slugs with roughly tuberculate skin that are found throughout the Holartic region. One of the most striking members of the family is Arion ater. As can be seen in the picture below, colour is variable with orange, reddish brown, brown and black forms present. A. ater is indistinguishable from the species A. rufus, except by dissection. It shows an interesting defensive reaction if irritated by contracting into a hemispherical shape and swaying from side to side (Pfleger, 1990 Molluscs p. 82). A. ater is omnivorous, feeding on carrion, fungi as well as dead and living plant material which marks it out as an agricultural pest.

Arion ater

Biological control of A. ater with the parasitic nematode Phasmarhabitis hermaphrodita has proved quite successful. Wilson et al. (1999, Biological Control 16 pp. 170-176) showed that A. ater actively avoided soil treated with the nematode. A control strategy employing P. hermaphrodita would therefore have the effect of protecting crops yet not wiping out slug populations.

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