Flying Spiders? And Space Weather?

Believe it or not, some spiders “fly”, it’s called ballooning, and apparently it’s due partly to space weather. So, how do they do it and what does space weather have to do with it?

This comes from the spaceweather.com website: Our thanks to Dr. Tony Phillips and spaceweather.com.

SPIDERS AND SPACE WEATHER: Did you know that spiders can fly? Biologists call it “ballooning.” Spiders spin a strand of silk, it juts into the air, and off they go. Airborne arachnids have been found as high as 4 km (2.5 Mi) off the ground. Originally, researchers thought spiders were riding currents of air, but there’s a problem with that idea. Spiders often take flight when the air is calm, and large spiders fly even when air currents are insufficient to support their weight. It’s a mystery.

Scientists from the University of Bristol may have found the solution. In a paper published in the July 5th edition of Current Biology, they proved that spiders can propel themselves using electric fields.

“We exposed adult Linyphiid spiders (Erigone) to electric fields similar to those which naturally occur in Earth’s atmosphere,” explains the paper’s lead author, Erica Morley. “Spiders showed a significant increase in ballooning in the presence of electric fields.” A remarkable video of their experiment shows one spider flying when the fields were switched on, then sinking when the fields were off again.


Above: This diagram, borrowed from K. A. Nicoll’s review paper “Space Weather influences on Atmospheric Electricity,” illustrates the role of thunderstorms and cosmic rays in creating Earth’s electric fields.

The electric fields spiders use for propulsion are part of Earth’s global atmospheric electric circuit (GEC)–a planet-sized circuit of electricity that researchers have known about since the 1920’s. In a nutshell, thunderstorms help build up a charge difference between the ground and the ionosphere 50 km  (31 Mi.) overhead. The voltage drop is a staggering 250,000 volts. This sets up electric fields linking Earth to the edge of space. Cosmic rays ionize Earth’s atmosphere, turning it into a weak conductor that allows currents to flow through the GEC.

Peter W. Gorham of the Dept. of Physics and Astronomy at the University of Hawaii notes that “the complex protein structure of spider silk includes charge-bearing amino acids glutamic acid and arginine, which might be generated in a charged state as part of the spinning process.”

Spiders have been observed using multiple strands of silk that splay out in fan-like shapes. Instead of tangling as they move through the air, the strands remain separate. Are they repelled by an electrostatic force? The work of Erica Morley and her collaborator Daniel Robert provides insight.


Above: Hairs on the legs of spiders called “trichobothria” twitch when electric fields are present–a signal to the spider that ballooning may commence. From “Electric Fields Elicit Ballooning in Spiders.” 

All of this raises the possibility that spiders may be affected by space weather as electric fields are perturbed by cosmic rays and solar activity. Research groups have demonstrated connections between space weather and atmospheric electricity on a variety of time scales:

  • Days: Coronal mass ejections (CMEs) from the sun can sweep aside cosmic rays as they pass by Earth, causing temporary reductions in atmospheric ionization as large as 30%. Our own Spaceweather.com/Earth to Sky cosmic ray balloons have measured these events. [ref]
  • Months: Measurements at the Reading University Atmospheric Observatory in the UK have shown that voltages can fluctuate +-15% as Earth dips in and out of the heliospheric current sheet (a huge corrugated magnetic structure centered on the sun) every ~27 days. [ref]
  • Years: During the 20th century, fair weather atmospheric voltages at sites in Scotland and the UK decreased by factors of ~25% due to a long-term decrease in cosmic rays. [ref] That slow trend is now reversing itself as cosmic rays intensify again.

Could the migration patterns of ballooning spiders be affected by space weather?

“It’s entirely possible, but we simply don’t yet know,” says Morley. “The experiments we have carried out are mostly lab-based, which helps eliminate confounding variables. A next step in the project is to take this all into the field and look for patterns. Factoring in solar activity could be very interesting.”

Who would’ve thought?