The conserved optimality of vertebrate limbs vs. Darwin.

 

Primordial WiFi?

 Biological Information in Static Electricity

David Coppedge

Insects and spiders know how to read the air when static electricity is present. Electrical charge, to them, is a source of biological information, says Daniel Robert in Current Biology in his Primer on “Aerial Electroreception.”

This newfound sensory modality reveals a previously unrecognised source of information, a new informational ecological niche integral to diverse life histories and navigational abilities, which remarkably involves animals, plants and atmospheric electricity

Arthropods live in an “electric ecology” where “electrostatics is everywhere, always, and all at once.” They come equipped with antennae and tiny hairs that are sensitive to the electrical environment. Sensing a charge, however, is only a part of the story. How do these organisms utilize the information? What does it tell them? How does it trigger a response?

Coulomb’s Law

In a brief review of electrostatics (as opposed to electrodynamics, which involves charges moving near the speed of light), Dr. Robert discusses electric fields and Coulomb’s Law — the principle that like charges repel and opposite charges attract. He notes that “electric fields are ubiquitous in the presence of matter.” He then links electrosensitive abiotic materials with electrosensitive biological materials.

In essence, electrostatics provides a framework for understanding how a static imbalance in charge distribution can ensue between materials, and how forces arise from it. Biological materials are evidently not exempt from such processes, and it is proposed here that electrostatics plays a discrete yet pervasive and significant role in the informational ecology of terrestrial organisms.

Those terrestrial organisms include plants. Flowering plants can fashion the electric ecology for pollinators, as I discussed in an article about floral electric fields that attract bumblebees. See also my article, “Bioelectricity Gives Biologists a Jolt.” Professor Robert’s article extends the concept of the electric ecology to wider dimensions.

While humans are only weakly sensitive to electrostatic charges in air, those charges are large for small organisms like arthropods. “It has become increasingly clear that many organisms tend to be electrically charged,” he says. In fact, “it is actually very difficult to find objects, biological or else, that are not charged.” A flying insect, therefore, can “feel” the electrical field in its environment with its sensory equipment and react if it has the mechanical equipment and brain software to know how to use the information.

Crucially, these ubiquitous electrical fields generate the Coulomb forces between charged objects that are measurable and putatively useful to organisms. Thus, do electric fields have the potential to be a source of information for animals and plants to organise their lives in space and time?

The Answer Is Yes

The influence of static charge in pollination is one demonstrable case — not only for bees, but for moths and hummingbirds as well. A flower, “grounded” to ground (a net source of electrons), attracts a bee that accumulates a positive charge flying through air. The apex of the plant will be the most negatively charged due to the atmospheric potential gradient (APG) that increases the electric potential 100V for every meter above ground. While the Coulomb attraction would be too weak to move the entire insect, its sensory hairs and antennae feel a tractor beam drawing them to the flower. 

Charges without sensors cannot use information in the electric ecology. But with its tiny hairs, antennae, and wings which “can act as charged dielectric surfaces,” the insect might be able to carry and store electrical information for communicating with other bees in the hive. This fascinating and only recently investigated phenomenon is probably true of most arthropods since all are equipped with similar sensors.

In effect, these structures are present in nearly all species of terrestrial arthropods. The notion thus arises that such processes of aerial electroreception may be widespread, though other mechanisms of detection cannot be excluded. It can be highlighted that these sensory hairs can be sensitive to air currents and sounds, in addition to electric fields. Here, it is expected that hairs, as long, thin, sharp and protruding structures, will tend to accumulate charge and engage in electrostatic interactions. Hair canopies constitute a distributed array of sensors, sometimes covering the entire arthropod body. Theoretical work shows that dual acoustic and electric detection of hair arrays can extract rich information, sensing the position and distance of external charges.

Other Examples of Electroreception 

Professor Robert gives other examples of electroreception. A caterpillar might sense the approach of a wasp. “Reciprocally, the capacity of wasps to detect caterpillars electrostatically should be considered,” he writes, “which also raises the enticing possibilities of electric crypsis, masquerade, and/or aposematism.” Spiders that use ballooning with silk threads to travel long distances might be utilizing Coulomb forces to lift themselves up through the APG. And unfortunately for large mammals, their fur can accumulate thousands of volts, potentially helping parasites like ticks ride the electrostatic tractor beam to their skin.

These are just a few of the research possibilities in the new field of aerial electroreception. Professor Robert’s article is intriguing, but sadly, he attributes causal powers to evolution, committing the fallacy that evolution searches for phenomena to exploit. The maxim “opportunity knocks” works for humans with foresight, but mutations and natural selection couldn’t care less if static electricity is in the air or not. Without operational sensors and instincts built into an organism from the start, nothing would happen.