The morphological heterogeneity of cricket flow-sensing hairs conveys the complex flow signature of predator attacks

Abstract

Arthropod flow-sensing hair length ranges over more than an order of magnitude, from 0.1 to 5 mm. Previous studies repeatedly identified the longest hairs as the most sensitive, but recent studies identified the shortest hairs as the most responsive. We resolved this apparent conflict by proposing a new model, taking into account both the initial and long-term aspects of the flow pattern produced by a lunging predator. After the estimation of the mechanical parameters of hairs, we measured the flow produced by predator mimics and compared the predicted and observed values of hair displacements in this flow. Short and long hairs respond over different time scales during the course of an attack. By harbouring a canopy of hairs of different lengths, forming a continuum, the insect can fractionize these moments. Short hairs are more agile, but are less able to harvest energy from the air. This may result in longer hairs firing their neurons earlier, despite their slower deflection. The complex interplay between hair agility and sensitivity is also modulated by the predator distance and the attack speed, characteristics defining flow properties. We conclude that the morphological heterogeneity of the hair canopy mirrors the flow complexity of an entire attack, from launch to grasp.