Benutzer:Muhali/Luftschiffen

Spiderlings ballooning in the Santa Cruz Mountains of the San Francisco Peninsula

Luftschiffen nennt man den Vorgang, bei dem sich Spinnen in die Luft erheben und fliegend mehrere hundert Kilometer zurücklegen können. Dies geschieht, indem die Spinne bei Wind mehrere Dutzend Seidenfäden produziert, welche dann mitsamt der Spinne davongetragen werden. Neueste Forschungen beschreiben ein ähnliches Verhalten auch bei Windstille, bei welcher die Spinnen elektrische Felder als Antriebsenergie nutzbar machen. Sinn und Zweck des Spinnenflugs sind bisher nicht vollständig geklärt.

Vorwiegend junge und sehr leichte Spinnen, aber auch die erwachsenen Exemplare der Baldachinspinne, starten ihren Flug von besonders exponierten Stellen. Sie beginnen wie auf Zehenspitzen zu trippeln und schießen dann aus ihren Spinnwarzen am Hinterleib ein ganzes Bündel von Fäden in die Luft, die sich wie eine Art Fächer aufspreizen. An diesem Gebilde hängend segeln die Tiere dann durch die Luft. Bei günstigem Wind können die Tiere sogar in den Jetstream gelangen und ganze Ozeane überqueren. Viele Spinnen überleben diese Reise allerdings nicht.

Beschreibung

Xysticus audax tiptoeing, in preparation for ballooning

Der Flug der Spinnen und anderer Wirbelloser beginnt meistens an Wind-exponierten Stellen, wo sich die Tiere strecken ("trippeln") und ein Gespinnst von 50-60 extrem leichten Seidenfäden spinnen und aussondern.[1] Dieses "Segel" kann sie bis zu mehreren Kilometern Höhe in die Luft und über sehr große Entfernungen davontragen. Dadurch waren sie etwa schon 1832 auf der Beagle von Charles Darwin gelandet, hundert Kilometer von der Küste Argentiniens.

These automatically form a triangular shaped parachute which carries the spider away on updrafts of winds where even the slightest of breezes will disperse the arachnid. The Earth's static electric field may also provide lift in windless conditions. Ballooning behavior may be triggered by favorable electric fields.

Many spiders use especially fine silk called gossamer to lift themselves off a surface, and silk also may be used by a windblown spider to anchor itself to stop its journey. The term "gossamer" is used metaphorically for any exceedingly fine thread or fabric. Biologists also apply the term "balloon silk" to the threads that mechanically lift and drag systems.Vorlage:Elucidate

It is generally thought that most spiders heavier than 1 mg are unlikely to use ballooning. Because many individuals die during ballooning, it is less likely that adults will balloon compared to spiderlings. However, adult females of several social Stegodyphus species (S. dumicola and S. mimosarum) weighing more than 100 mg and with a body size of up to Vorlage:Convert have been observed ballooning using rising thermals on hot days without wind. These spiders use tens to hundreds of silk strands, which form a triangular sheet with a length and width of about Vorlage:Convert

In Australia, in 2012 and in May 2015, millions of spiders were reported to have ballooned into the air, making the ground where they landed seem snow-covered with their silk.

Distance and height achieved

Threads of silk following a mass spider ballooning

Most ballooning journeys end after just a few meters of travel, although depending on the spider's mass and posture, a spider might be taken up into a jet stream. The trajectory further depends on the convection air currents and the drag of the silk and parachute to float and travel high up into the upper atmosphere.

Many sailors have reported spiders being caught in their ship's sails over Vorlage:Convert from land (Heimer 1988). They have even been detected in atmospheric data balloons collecting air samples at slightly less than Vorlage:Convert above sea level. Evidently, ballooning is the most common way for spiders to invade isolated islands and mountaintops. Spiderlings are known to survive without food while travelling in air currents of jet streams for 25 days or longer.

Some mites and some caterpillars also use silk to disperse through the air.Vorlage:Citation needed

A close association has been found between ballooning behaviors and the ability for a species of spiders to survive afloat on water. Water-repellent legs keep them alive on both fresh and salt water, enabling them to survive waves up to 0.5 metres in height. In wind many species raised their legs or abdomens to use as sails, propelling themselves across the water's surface. Many species of spiders also drop silk to anchor themselves in place while afloat. Said spiders did not show these behaviours on land, suggesting that they are adaptations to water.Vorlage:Clear

See also

• Aeroplankton
• "A Noiseless Patient Spider", a poem by Walt Whitman based on spider ballooning behaviour
• Organisms at high altitude
• Spider silk

Further reading

• Vorlage:Aut (1985): Size of ballooning spiders at two locations in eastern Texas. J. Arachnol. 13: 111–120. PDF
• Vorlage:Aut (1988): Wunderbare Welt der Spinnen. Urania-Verlag Leipzig. Vorlage:ISBN.