When Spiders Fly

One of my favorite parts about being a scientist is the exposure I receive to discoveries that are lethal for how I characterize the world around me. It is so easy to be enveloped by our everyday experience that we construe as reality that relies only on what our senses can tell us. One such discovery that was particularly transformative was from a paper released in 2018 about how spiders use the electric field to navigate the world. 

Those interested in studying the atmosphere would collect samples from flights at different altitudes. To their surprise, they found more spiders than one would expect at altitudes of 10,000 feet. Wingless bugs in the collection filter. Odd. Ecologists like Charles Darwin mused for years about the way spiders took flight in an action called ballooning. During ballooning, spiders point their abdomen in the air, get on their tip-toes (I know right), and project strands of silk into the air. The strands waver without tangling, and perplexingly without apparent cause, the spider lifts into the air and drifts away. From a human perspective, the intuitive cause for this lift would be some kind of mechanical force like wind that pushes the spider into the air, like the wind could push a boat on the water. Spiders are small, and the right air current at the right time could explain this phenomenon. Some experiments were done, and spiders seemed to balloon when wind speeds were very low. Besides, that idea is the only one the narrow sensory landscape of my mind can accommodate so let’s stop there?

No. 

Erica Morley and Daniel Robert, the researchers who investigated the impact electric fields have on spiders, noticed some odd inconsistencies about wind being the only factor for inducing ballooning. First off, spiders have been observed to balloon in sunny, windless conditions. Second, if low wind speeds are preferred for flight, how could that force generate the lift needed to get them going in the first place? Lastly, if the wind was so important, why is it that the silk strand spiders shoot as they tip-toe and prepare to balloon do not tangle amongst themselves? To some, the inconsistencies were too glaring and invoked a new perspective. What if the electric field generated between the earth and its atmosphere was contributing to this quirky phenomenon. 

What follows are some provocative experiments that demonstrate the impact a changing electric field in a windless environment has on spider behaviors correlated with ballooning, like tip-toeing and abdomen pointing. When there is no electric field, the spiders will hang out and remain ground dwellers. But as the electric field strength increases more and more, the spiders get on those tippy-toes and start shooting strands of silk into the air.

Okay, so it seems plausible that the spiders use the electric field to gauge conditions for flight. But the natural question that arises is, how? As it turns out, spiders possess these microscopic hairs on their legs called trichobothria. They found that changing the electric field would necessarily deflect the trichobothria versus other, non-electrical sensing hairs. So there we have it, spiders use these little hairs to sense the conditions of the electric field and will shoot strands of silk to drag them into the air. Spiders do not fly, they levitate. If that is nightmare fuel for you, please watch this video where the authors use electric fields to levitate a spider.