Can small spiders be interesting?

Alastair Lavery, SAERI Senior Research Fellow.

With my artistically accomplished colleague Rowley Snazell, we have just published the second part of our account of the spiders of the Falkland Islands, adding six new species to the island list and describing 4 species new to science and endemic to the Islands (Ref 1). All the spiders in this account are members of the Linyphiidae, the money spiders The money spiders are small web-spinners, catching insects in horizontal, hammock-shaped webs spun deep in vegetation. They are often overlooked, being small - most of the species on the islands are about 2mm body length - and spend most of their time sitting and waiting on webs near ground level.
The spiders of greatest interest belong to the genus, Falklandoglenes. The Falklandoglenes story begins in 1980 when a group from British Antarctic Survey, following pioneering work by the late Ian Strange, visited Beauchene Island, including “a preliminary survey of the invertebrate fauna” in there aims (Ref 2). They caught 55 spiders, passed to Michael Usher, then at the University of York. Usher identified 7 species, 4 of which he described as new species (Ref 3).

Image: Falklandoglenes weddelli - Adult Female
One of Usher’s new species was Falklandoglenes spinosa, the type species of a new genus. There were only 4 specimens found and only 2 of these, one male and one female, were adult. The spider had several unusual characteristics which led Usher to place it in an Australian subfamily, the Mynogleninae. Over the next decades our knowledge of the spider fauna of southern South America has been transformed and Falklandoglenes’ place as a Neotropical genus is now clear, even if its exact relationship remains unknown.
I spent a month in 2004 collecting spiders across much of the islands, and a second Falklandoglenes came to light, on East Falkland. Unlike F. spinosa, living on its single, remote island, this species is found round Stanley, with many records from the Gypsy Cove area, but also on Weddell, Keppel and West Point Islands. The first I found was at Hadassa Bay, so this is now Falklandoglenes hadassa, the smallest and most widespread of the species.

The next Falklandoglenes to be found was on Steeple Jason in 2005, as part of the Invertebrate Survey. Only 3 specimens were collected and only two of these were adult. It was very similar to Falklandoglenes spinosa but with one very obvious difference, while F. spinosa is 4.2mm in body length, the Steeple Jason specimens are 3.3mm long. Looking at the type of F. spinosa and the male from Steeple Jason in the labs at the Natural history Museum in London I was convinced that more specimens were needed. More were collected on Steeple Jason in 2018 by Falklands Conservation and showed that it had slight but consistent difference in its genitalia, especially in the female. So it is a new species, Falklandoglenes iasonum, only found on Steeple Jason.

The final species had to wait until I returned in 2010 and visited Weddell Island, where a very distinctive member of the genus was found, Falklandoglenes weddelli. Weddell Island has the distinction of being the only island where 2 species of the genus have been found, but F. weddelli is only known from Weddell Island.

There are four species of Falklandoglenes, all restricted to the Falkland Islands, spread across the islands and with only one exception, not overlapping.

How did they get here?
The distribution suggests an ancestor species from the continent has speciated across the islands. It will need more survey and detailed DNA analysis to work out if this is the case.

Are there more of them?
A lot of the Falkland Islands has not been checked for small spiders, and there is every likelihood that either the 4 species we have here, or other new ones, will be found in some of the unexplored areas.

Can they survive?
Any species with isolated island populations is at threat and 3 of the 4 species here fall into that category. It applies in particular to F. spinosa. In 2011 Sarah Crofts from Falklands Conservation collected spiders from Beauchene during a seabird census visit. Only 12 specimens were found, but these represented 4 of Usher’s 7 species. F. spinosa was not found. The species has not been recorded since the initial collection of 4 specimens in 1980. It must be one of the least known and most threatened spiders in the world.

Another threat is a European introduced and potentially invasive species, Tenuiphantes tenuis, a spider with similar feeding habits to Falklandoglenes. First found in gardens in Stanley in 1987, when last surveyed in 2010 it had spread as far a Cape Pembroke, Murrell Valley and Wall Mountain, 12 km from Stanley. It’s spread is slow and we don’t know how it interacts with F. hadassa, but globally the contest been island species and invasives has been ominous.

So, can a group of small (2mm-4mm) spiders, hiding in the vegetation, and literally overlooked by most naturalists, be interesting? Obviously, I think so.

My fieldwork was supported by the Shackleton Trust, Falklands Conservation and the RSPB.

*LAVERY, A. H. & SNAZELL, R. G. 2023: The spiders of the Falkland Islands 2: non-erigonine Linyphiidae. Arachnology 19: 681-698. Ref 1

*LEWIS SMITH, R.I. & Prince, P.A. 1985: The natural history of Beauchene Island. Biological Journal of the Linnean Society 24: 233-283. Ref 2

*USHER, M.B. 1983b: Spiders from Beauchene Island, Falkland Islands, South Atlantic. J.Zool. Lond 200: 571-882. Ref 3

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