Pillars of Defense

Hover fly cuticles are covered in tiny spikes called nanopillars.

Cross-section of a hover fly larva cuticle, showing nanopillars extending from the surface

Matthew Hayes

Amidst growing concern about evolved resistance to antibiotics, there is increasing interest in the physical ways in which the natural world avoids infection. A new study of drone flies suggest that their cuticles have tiny spikes, creating a surface that makes it difficult for bacteria to colonize.

Hover flies (Eristalis tenax), a type of drone fly, are found on every continent except Antarctica. Their adult form, a mimic of bees and wasps, is familiar. Their larval form, however, is much more “grotesque” and poorly studied, says cell biologist Matthew Hayes, at University College London’s Institute of Ophthalmology.

As Hayes explains, hover fly larvae live in “nasty ponds” that contain little oxygen and an abundance of animal waste. Collecting larvae of these hover flies from ponds in Surrey, south of London, Hayes and fellow researchers Timothy Levine and Roger Wilson used scanning and transmission electron microscopy to take a closer look.

By not washing their specimens too vigorously before chemically fixing them for microscopy, the researchers deliberately preserved the biofilm—any sticky microorganisms clinging to the bodies of these wild-caught larvae. Then, by carefully examining the larval cuticle at high magnification, the researchers detected tiny prickles, which they refer to as nanopillars.

These skinny protrusions ranged in length from 200 to 1,000 nanometers. They also varied in how densely they were distributed across the larval cuticle. Where nanopillars were sparser, the researchers found more bacteria attached. But in areas of high nanopillar density, bacteria were virtually absent.

Hayes hopes that his nanopillar discovery in hover fly larvae will inspire further study of their structure and biochemistry. The novel geometry of these thin nanopillars, distinct from the structure of nanopillars previously uncovered on cicada and dragonfly wings, may generate ideas for biomimetic antifouling surfaces. (Journal of Insect Science)