Newsletter of the Opiliones
Editor: Paul Hillyard
Many recorders have remarked that they are happy to see the new Ocularium. Good! I hope that it helps to maintain an active community. Now, I need your help to keep the newsletters interesting. Please do try to contribute some news, short articles or simple observations.
|SPREAD of Dicranopalpus ramosus|
The last issue of Ocularium referred to the spread of this unmistakable species. Well, judging from recent records, the speed of this harvestman's spread in Britain is quite amazing! Long legs obviously help! We now have two sites that are close on 54°N:
Jonty Denton reported: "It was abundant on a disturbed, scrubby, calcareous part of Thorpe Arch Trading Estate, formerly (in 1941-68) a munitions dump with railway connections to main lines etc." In a separate communication, Paul Whitehead wrote: "It is abundant in the English Midlands. It prefers large hedgerow trees, occurring well up in the crowns, and is frequent in sheltered, damp areas. It seems particularly able to use corridors of woody plants and appears to radiate rapidly along these. Adults are active into the early winter, and this may have been aided by recent climatic trends. Records from Shropshire seem to go back a few years." And according to Wayne Rixom: "A recent visit to the Queenswood area in Herefordshire resulted in countless examples of the species, often to the exclusion of other species on bushes, trees and even in tall grass in some cases."
Dicranopalpus ramosus was originally described from Morocco in 1909 (as Dicranochirus ramosus). The first record from Portugal was in 1948 (as Dicranopalpus caudatus); Spain in 1965 (D.caudatus); France in 1969 and Britain in 1957 (first record Bournemouth).
Sabacon viscayanum ramblaianum
|STATUS of Sabacon viscayanum ramblaianum|
The following is an edited extract from: Notes on the ecology and British status of the opilionid Sabacon viscayanum ramblaianum by I.K.Morgan (1990), Dyfed Invert. Grp. Newsl. 19: 15-18.
The harvestman Sabacon viscayanum subsp. ramblaianum Martens was first discovered in the British Isles in September 1980 in woodland at Parkmill, Gower, Glamorgan (Abbot, 1981). By 1990 it was known from 13 localities in the southern half of Wales with a concentration in SE Carmarthenshire. Today, in 1999, it is known from 22 sites in S Wales (27 records) plus one near Presteigne, actually just in England: SO299622 (Wayne Rixom, 1999).
Because the early finds were close to industrial workings, it was suggested (Merret in Hillyard and Sankey, 1989) that the harvestman had been introduced to Britain. However, these sites include old, damp woodland which is in fact the usual habitat of Sabacon. Martens (1983) considers S.viscayanum to be a 'Tertiary relict species', i.e. a taxon whose range was once more extensive but which has since become fragmented. Relict species are considered to be in 'evolutionary decline' and thus it seems unlikely that S.viscayanum could establish and thrive after being introduced into Britain. Recent work on the habitat preferences of S.viscayanum in S Wales concurs with Abbot: "The species of Sabacon are found in moist, cool habitats, high altitudes or temperate climates. They prefer woodland, especially wet, shaded dingles, and can be found under decaying logs and in leaf litter. They are sometimes found in caves." Thus if Sabacon had been introduced into Britain, the means of introduction would have had to maintain the required coolness and high humidity. It is difficult to imagine such a mechanism. More needs to be known about the distribution of Sabacon in Britain and Europe. It should perhaps be looked for in SW England and S Eire.
Abbot, R.H.R. 1981. A new opilionid to Great Britain. Newsl. Br. arachnol.. Soc. 30:4.
Martens, J. 1983. EuropaischeArten der Gattung Sabacon Simon 1879 (Opiliones: Sabaconidae). Senckenberg Biol. 63: 265-296.
|MASS AGGREGATIONS of HARVESTMEN|
Has anyone seen any aggregations lately?
J.G. Wood wrote: "One day this summer (1862), as I was bathing in the river Cray, just below a lasher, I happened to look under the cross-beam of the woodwork, and there saw something which I took for a mass of black horsehair. Wondering how such a substance could get into such a situation, I went to examine it and then found that the supposed horsehair was nothing more or less than a legion of harvest-spiders, all gathered together, their little bodies nearly hidden by bent legs. There must have been some thousands of the creatures under the beam, all perfectly motionless." [probably leiobunids - ed.]
It is most probable that aggregations form because the combined action of many opilionids' stink glands repels predators more effectively than one individual's effort. Vertical surfaces and protected spaces are the preferred sites for this group behaviour. For example, in Mexico, aggregations form in the branches of the candelabra cacti. A paper by Holmberg et al. (1984) on overwintering Leiobunum paessleri, in Canadian caves and mines, distinguished two types of aggregations: "loose" and "dense". In "loose" aggregations, the bodies of the opilionids were orientated in different directions with the legs outstretched or flexed. In "dense" aggregations, consisting of several layers of densely-packed opilionids, mostly with legs hanging straight down, the individuals in the innermost layer clung on to the substrate by the claws of their pedipalps or chelicerae. At the same time, the outermost layers clung on to the bodies of the innermost (like on the London Underground!).
Holmberg, R. G., Angerilli, N.P.D., and LaCasse, L.J. 1984. Overwintering aggregations of Leiobunum paessleri in caves and mines (Arachnida, Opiliones). J.Arachnol., 12:195-204.
Wood, J.G. 1863. The Illustrated Natural History. Routledge & Sons, London, page 677.
|BBC HARVEST FESTIVAL|
Harvestmen were described for the uninitiated in an article in the October 1999 issue of BBC Wildlife Magazine. The article can be read at the website: www.bbc.co.uk/animalzone.
|RECORD CARDS SUBMITTED|
Many thanks to the following recorders for submitting records last year: Adrian Colston, A.E. Cooper, S.J.Gregory, J. E. Milner, I.K.Morgan, and T.J.Thomas.
Specimen received from Peter Harvey, collected at Banbury Reservoir, Lea Valley, belongs to a species of Opilio new to Britain. Full account next issue.
All material is
Copyright British Arachnological Society and Opiliones Recording
© British Arachnological Society and P.D.Hillyard 1999
Printing of this publication for educational purposes is permitted, provided that copies are not made or distributed for commercial gain, and the title of the publication and its date appear. To copy otherwise, or to republish, requires specific permission from the Editor.