Up through the atmosphere

Abstract

Organismal Biology![Figure][1] Spiders stand on prominences, emit strands of silk, and take to the air. PHOTO: ZUMA PRESS/ALAMY STOCK PHOTO Surprisingly, a major component of the diet of swifts is spiders. Swifts only stop flying when they are breeding, so how do the spiders on which they feed become airborne? Morley and Robert discovered that spiders are sensitive to electric fields, so that they respond to the atmospheric potential gradient. The electric field mechanically activates hairs (trichobothria) on the spiders' legs. Formation of a vertical electric field stimulates a spider standing on top of a plant to release fine threads of silk and let go. The electric field strength of pointed leaves can achieve tens of kilowatts per meter in mildly unsettled weather, and the atmospheric potential gradient provides enough coulomb force to lift a spider into the air without any help from passing breezes. The next thing to work out is what the advantages are to spiders to ascending sometimes thousands of meters into the atmosphere—it isn't just to offer themselves as tidbits to swifts. Curr. Biol. 28 , 2324 (2018). [1]: pending:yes