Ballooning with Spiders

On October 29^th Darwin was visiting old friends around town – enjoying time back in the trappings of “culture” (as defined by a 19^th century Englishman from a prominent family):

“Walked round the fortifications; & entered the country through the gate by which the English took M: Video.— The degree to which the ground near to the city is strewed with the bones of cattle & horses is truly astonishing & quite corresponds to the annual vast export of hides.— In the evening dined with Mr Parry & met there Cap. Paget of the Samarang.— Our old friend the Samarang came here a few weeks after we sailed to the South.— the Druid having gone to England.” (Oct 29)

As much fun as he probably had with Captain Paget and his other comrades, I’m sure Darwin was happy to be on his way again and seems downright excited to be sailing to Buenos Aires. Alas the Beagle struggled with the winds all day on the 30th:

“We got under weigh early in the morning for Buenos Ayres, but a fresh breeze right in our teeth lasted the whole day; so that when we anchored at night, we had not made much progress.” (Oct 30)

On the 31^st progress was still slow, but for Darwin, the day still held beauty in the form of spiders, sailing on silver threads and filling the rigging with gossamer sails.  He writes:

“A beautiful day: but the wind has been steadily against us.— In the evening all the ropes were coated & fringed with Gossamer web.— I caught some of the Aeronaut spiders which must have come at least 60 miles. How inexplicable is the cause which induces these small insects, as it now appears in both hemispheres, to undertake their aerial excursions.” (Oct 31)

What Darwin describes here (appropriately for Halloween :)) is the ability of some spiders to “fly” using a process known as “ballooning”. These spiders (usually recently born) climb to a high point were they make a triangular “sail” out of silk.  The air currents lift the spider by the sail – up, up and away.  Some spiders drift a few meters and come back to Earth, but others can get carried away on the winds for great distances. Weather balloons have detected ballooning spiders at 5 km above sea level, and some have been known to travel over 1600 km out to sea.  Evidence of this amazing feet is also found in the fact that one of few living things found high up near the peak of Mt. Everest are spiders. It’s no wonder that they are also one of the first group of animals to colonize a new volcanic landscape or ocean island. Heck, if they were able to take a large bubble of air with them, they might be the first animals to survive leaving he Earth!

Crab spider preparing to balloon from scienceblogs.com

(RJV)

PS – And to think, I grew up thinking that this guy was Gossamer!

Happy Halloween!