European Spider of the year 2009 - The triangle spider
Hyptiotes paradoxus (C.L. Koch 1843)

Almost everyone is familiar with the typical orb-web of the garden spider. It is also widely known that over millions of years nature has altered some organisms and their behaviours into sometimes quite bizarre forms. The spider of the year 2009 shows us how the classic spider web can be modified into an ingenious prey-capture device.

First though: the protagonist is inconspicuously small (3–6 mm body length), inconspicuously coloured (pale grey, brownish or darker, often with a pattern of lighter, partly feathery hairs) and lives hidden, mostly among dry twigs in the inner parts of pine forests. The spider is noticeable stocky, both in its legs and body, and is wonderfully camouflaged against its environment. The abdomen has the shape of a raised triangle and this may well have been decisive in naming the spider. Yet it is the web which gives this spider most clearly away. As you wander through the pine forests, its best to let the sunlight reveal the ca. 20 cm large webs as it shines against them. These webs are built from only four radial threads, plus the capture threads which are held taught between them; i.e. it makes up three segments from a complete orb web. The web is held in place by support threads on one side and a signal thread emerging from the hub on the opposite side. Overall, it looks like a silken triangle. Hyptiotes has, as it were, the strands of its web to hand and sits, waiting, between the hub and the attachment point; effectively forming a living part of the signal thread. If an insect lands in the capture threads, the spider instantly lets the trap snap shut by increasing the length of the supporting thread behind it, reducing the tension in the rest of the web. In this way the capture threads collapse over the prey, leaving the web-maker with an easy job of finishing things off.

For arachophobes this spider is a ray of hope as it has – like all members of the cribellate orb-weavers (Family Uloboridae) – no poison glands. Like the orb-web, these glands have been reduced during evolution. Prey is simply wrapped into an immovable mass, which means that during digestion the silk must be eaten first to allow the spider to get at the nutrients in the prey. As in all spiders, this occurs through preoral digestion in front of the mouth.

Another unusual feature, which the triangle spider shares with about 50 species Europe-wide, is cribellate silk. To explain this, it is important to first see how the spinnerets are constructed. Normally spiders have six spinnerets – short highly-modified and reduced appendages at the back end of the abdomen. On these spinnerets sit spigots which are connected to the silk glands inside the body. Silk emerges from the spigots and can be used for, e.g., supporting threads or building egg cocoons. Cribellate spiders have, in addition to the six spinnerets, a sieve-like ‘cribellum’ which sits directly in front of these spinnerets. It is probably homologous with a fourth pair of spinnerets which were present in ancestral spiders and can still be found in a handful of primitive forms. Thousands of single threads are produced by the fine spigots on the cribellum. These threads are combed out by a calamistrum: a special row of comb-like hairs on the last pair of legs. This produces ‘woolly’ capture threads. These are four times more adhesive than the sticky threads of the garden spider and have the advantage that they don’t need to be replaced regularly because of the drying-out of the glue.

Finally, another anatomical absurdity of Hyptiotes paradoxus should be mentioned. Due to their lack of a penis, all male spiders have to transfer their sperm indirectly. They do this with the aid of copulation organs located on their pedipalps – the appendages between the mouthparts and the first walking legs. In almost all spiders these organs are of a small or moderate size. In Hyptiotes, however, the volume of the palpal organs is almost the same as the whole front part of the body.

Despite all these peculiarities, the triangle spider is also a common spider and can be found from western Europe through to east Asia. It occurs in woodland and its genus name (“one who lies on their back”, “the inactive” in reference to its normal resting position) suggests something rather relaxed. It goes without saying that camouflaging itself and lying very still are important for survival. The species name paradoxus (“the strange or paradoxical”) makes us curious to learn more about this spider. If during the period of maturity (July to October) you can spare a couple of hours, and if you want rest your bad back with a walk across soft and fragrant pine needles, then why not visit the triangle spider in its world!

Peter Jäger

English translation: Jason Dunlop

Contact
Germany:
Dr. Martin Kreuels, 48161 Münster, Nordrhein-Westfalen (NRW)
Email: kreuels (at) aradet.de
Europa:
Dr. Milan Řezáč, Department of Zoology, Charles University, Vinicna 7, 128 44 Praha 2, Czech Republic, eMail: pavouk.milan (at) seznam.cz

Countries involved (Number of countries: 21, Number of jury members: 71):
Austria, Belgium, Bulgaria, Czech Republic, Denmark, Finland, France, Germany, Great Britain, Hungary, Ireland, Italy, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland.

Supporting organisations:

• Arachnologische Gesellschaft e.V. AraGes (http://www.arages.de/)
• Belgische Arachnologische Vereniging/Société Arachnologique de Belgique ARABEL ( http://www.arabel.ugent.be/)
• European Invertebrate Survey-Nederland, Section SPINED
• Grupo Iberico de Aracnologia-Sociedad Entomologica Aragonesa GIA ( http://aracnologia.ennor.org/web_intro.html)
• Society of European Arachnologists SEA ( http://www.european-arachnology.org/)

Distribution maps and photo galleries:

Germany
http://www.spiderling.de/arages/Verbreitungskarten/ (Distribution map)
http://www.spiderling.de/arages/Fotogalerie/
http://www.natur-in-nrw.de/HTML/Tiere/Spinnen/

Europa
http://www.spiderling.de/arages/OverviewEurope/
http://www.eurospiders.com/Hyptiotes_paradoxus.htm

Literature:

Bayram, A., S. Özdag & R. Kaya (2002):
New spider (Araneae) records for Turkey: Hyptiotes paradoxus (C.L.Koch, 1834) [Uloboridae], Diaea pictilis (Banks, 1896) [Thomisidae)], Alopecosa fabrilis (Clerck, 1757) [Lycosidae], and Evarcha arcuata (Clerck, 1757) [Salticidae]. — Israel Journal of Zoology 48: 250–251.
BELLMANN, H. (1997):
Kosmos-Atlas Spinnentiere Europas. — Stuttgart, Kosmos: 304 S.
Dalton, S. (2005):
Prey Capture by Hyptiotes paradoxus. — Newsletter of the British arachnological Society 104: 17–18.
Decocq, O. (1996):
Une nouvelle donee d'Hyptiotes paradoxus (C.L.Koch, 1834) (Araneae, Uloboridae).- Nieuwsbrief van de Belgische Arachnologische Vereniging 11(1): 13.
HAJER, J. (1993):
Notes on the spinning apparatus of the spiders Hyptiotes paradoxus C.L.K, 1834, and Uloborus walckenaerius Latr., 1806 (Araneae: Uloboridae). — Bull. Soc. neuchatel. Sci. nat.:116 (1): 99–103.
Hawthorn, A. & B. Opell (2002):
How does cribellar silk thread stick to smooth surfaces? — American Arachnol. 64: 4.
Hopkin, S. (2002):
New locality for Hyptiotes paradoxus (C.L. Koch, 1834). — Newsl. Br. Arachnol. Soc.: 95: 10.
Horak, P. & C. Kropf (1999):
Landeskundlich bedeutsame Spinnenfunde in der Steiermark (Arachnida: Araneae). — Mitteilungen des naturwissenschaftlichen Vereins für die Steiermark 129: 253–268.
MARPLES, M.J. & B.J. Marples (1937):
Notes on the spiders Hyptiotes paradoxus and Cyclosa conica. — Proc. Zool. Soc. London 107 (3): 213–221, + 2 Tafeln.
Opell, B. D. (1982):
Post-hatching development and web production of Hyptiotes cavatus (Hentz) (Araneae, Uloboridae). — Journal of Arachnology 10: 185–191.
Opell, B.D. (1982):
Cribellum, calamistrum and ventral comb ontogeny in Hyptiotus cavatus (Hentz) (Araneae: Uloboridae). — Bull. Br. arachnol. Soc. 5 (8): 338–343.
Opell, B.D. (1987):
The influence of web monitoring tactics on the tracheal system of spiders in the family Uloboridae (Arachnida, Araneida). — Zoomorph. 107: 255–259.
Opell, B.D. (1988):
Prey handling and food extraction by the triangle-web spider Hyptiotes cavatus (Uloboridae). — J. Arachnol. 16: 272–274.
Opell, B.D. (2001):
Cribellum and calamistrum ontogeny in the spider family Uloboridae: linking functionally related but separate silk spinning features. — J. Arachnol. 29: 220–226.
Opell, B. D., G. Roth & P.E. Cushing (1990):
The effect of Hyptiotes cavatus (Uloboridae) web-manipulation on the dimensions and stickiness of cribellar silk puffs. — Journal of Arachnology 18: 238–240.
Peters, H.M. (1938):
Über das Netz der Dreieckspinne, Hyptiotes paradoxus. — Zoologischer Anzeiger 121: 49–59.
PETERS, H.M. & J. KOVOOR (1980):
Un complément à l'appareil séricigéne desd Uloboridae (Araneae): Le paracribellum et ses glandes. — Zoomorph. 96: 91–102.
REUKAUF, E. (1931):
Zur Biologie von Hyptiotes paradoxus. — Z. Morph. Ökol. Tiere 21: 691–701.
Spagna, J.C. & R.G. Gillespie (2007):
Unusually long Hyptiotes (Araneae, Uloboridae) sequence for small subunit (18S) ribosomal RNA supports secondary structure model utility in spiders. — J. Arachnol. 34 (3): 557–565.
Stahlbaum, G. (1961):
Zum Vorkommen einiger seltener Radnetzspinnen (Araneidae) im Kreis Neuruppin. — Märkische Heimat 5: 128–130.
Tutelaers, P. (2001):
Herfstspinnen bij onze hunebedden. — Nieuwsbrief Spined 16: 7–9.
WIEHLE, H. (1953):
Spinnentiere oder Arachnoidea. IX: Orthognatha - Cribellatae - Haplogynae - Entelegynae (Pholcidae, Zoradiidae, Oxyopidae, Mimetidae, Nesticidae). — In: F. DAHL, M. DAHL & H. BISCHOFF (Hrsg.): Die Tierwelt Deutschlands und der angrenzenden Meeresteile. 42. G. Fischer, Jena.
Wiehle, H. (1964):
Über Hyptiotes gerhardti WIEHLE (Arach., Araneae). — Senckenbergiana biologica 45: 81–85.
Williams, H. (2003):
Hyptiotes paradoxus (C.L. Koch, 1834): New record for Nottinghamshire. — Newsl. Br. arachnol. Soc. 98: 9.
Wunderlich, J. (2008):
Revision of the European species of the spider genus Hyptiotes Walckenaer 1837 (Araneae: Uloboridae). — Beitr. Araneologie 5: 676–684.
Yoshida, H. (1982):
Spiders from Taiwan II. Three species of the genera Hyptiotes and Miagrammopes (Araneae: Uloboridae). — Proc. jap. Soc. syst. Zool. 22: 18–20.
Zschokke, S. (2000):
Web damage during prey capture in Hyptiotes paradoxus (C. L. Koch 1834) (Uloboridae). — Arachnol. Mitt. 19: 8–13.