The biophysics of aerial electroreception in arthropods

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We recently discovered that bumblebees can detect and learn about the electric fields that arise when they approach a flower. A weak electric field indeed builds up as bumblebees, like other flying insects, tend to be positively charged, and flowers tend to have an excess of negative charges - electrons. Using experiments that teach bee to recognize flowers with sugar rewards, it was possible to show that bee can memorise which flower contains sugar rewards on the sole basis of the flower's electric field. New evidence shows that spiders can also use electric fields; this time to fly! We could indeed show in the lab and in the field, that spiders perform ballooning flights by casting in the air several strands of their finest silk. As the spider stands on its tiptoes on top a tall grass or leaf, their silk sail experiences an uplifting force from the electrostatics in the atmosphere. Interestingly, we could show that ballooning takes also place in the total absence of wind, solving a question that Charles Darwin asked himself as he observed thousands of tiny spiders alighting the riggings of his ship, the Beagle.Bumblebees are quite furry, a coat deemed useful to staying warm and collecting pollen. We wondered whether fine hairs can react to electric forces. We first imagined that bees may experience something similar to the hair-raising sensation we used to have when approaching an old television set. For bees and spiders, we measured the tiny hair movements as they are exposed to electric fields like those found in nature, using a fine beam of laser light. We thus discovered that bees and spiders have dedicated sensors -fine hairs- to detect weak electric fields. But do other insects detect electric fields, and why? We have chosen to study an important group of insects - beetles because they play crucial roles in global ecology and allow us to investigate other reasons why small insect may use electric fields. We have chosen ladybird larvae and dock beetles because they have distinct rows of fine hairs on their backs, the function of which is currently unknown. We hypothesise that negatively charged leaf dwelling insects use these hairs to electrically detect positively charged approaching flying predators and parasitoids, such as wasps and flies. In the field, we have observed that ladybird and dock beetle larvae react to the presence of an electric charge approaching them. We note that ladybird larvae have well-organized rows of hair tufts, the function of which is unknown. Here, we seek to establish whether the detection of electric field also pertains to predator or prey detection, functions that go beyond that of pollination and that is relevant to many insect species that play important roles in ecosystems and agriculture.Weak electric fields are pervasive in the natural environment, but apparently, are not sensed by humans. Our work also aims at increasing our awareness, shaping a better understanding of the electric environment, our electric ecology. Our research project therefore serves to developing new ways to measure and understand the existence of this potentially important component of the sensory ecology of humans, animals and plants. We will be collecting data and producing visual media that will make visible this thus far elusive part of the natural world. We will employ our novel electrical measurement and visualisation techniques, learning from the way small insects detect weak electric fields. Using 3D printing techniques, we will model, design and construct insect-like hair structures made of electrically chargeable plastics. This bio-inspired approach will contribute to the long-term impacts of this research. As such, our research will also provide scientific information enabling more general questions about the possible impacts of man-made electric fields on humans, the environment and the organisms supporting important ecological networks and services.