Optimal design of arthropod airflow receptors [with video]

The airflow detecting filiform hairs of spiders and crickets works optimally on a broad range of unexpectedly high frequencies. This suggests the existence of a constant evolutionary pressure on the reception of fast airborne signals, which might be crucial for detection of prey or predators against other signal sources.

HFSP Long-Term Fellow Brice Bathellier and colleagues
authored on Mon, 21 May 2012

Many arthropods such as spiders, scorpions, crickets or cockroaches express, on certain parts of their body, arrays of long, thin and light-weighted hairs which serve for detection of air flow movements. The most commonly known example of these so-called filiform hairs is the cercal hairs of many insects which are found on two appendages at the rear of their body and which are known to be essential for detection of predator attacks. In arachnids, filiform hairs are found mostly on the legs, and might, in addition to predator avoidance, be useful to detect the airflow signatures of prey.

 

 

Because it is very difficult to measure the airflow experienced by crickets and spiders in their natural environment, the spectro-temporal signatures of airflow signals which are behaviorally relevant to these various species is still not fully known. In this study, we proposed to investigate the mechanical design of filiform hairs to infer the type of signals they might be optimized for.

Filiform hairs are basically passive oscillators which are swung to and fro by surrounding air flows. Building on and improving previous models of the hair mechanics and of its hydrodynamic interaction with the flow, we identified a physical limit for the conversion of airflows into hair motion. This limit corresponded to a maximum amplitude (or energy) of oscillation that a passive hair could achieve, for a given airflow, over all possible values of its mechanical parameters.

Performing measurements of the response of cricket and spider filiform hairs to different air flow frequencies, we observed that in most of these hairs the physical limit was reached for a broad range of unexpectedly high air flow frequencies. These results indicated that filiform hairs, both in insects and arachnids, are optimized for the detection of broadband high frequency signals, which despite their low energy in the usually measured power spectrum of biological airflows, might be of high ecological importance.

Reference

Air motion sensing hairs of arthropods detect high frequencies at near-maximal mechanical efficiency. Bathellier B, Steinmann T, Barth FG, Casas J., (2012) J R Soc Interface., 9(71):1131-43. DOI: 10.1098/​rsif.2011.0690

Pubmed link