Many organisms increase the air or water flow adjacent to olfactory surfaces when exposed to appropriate chemical stimuli; such ‘sniffing’ samples fluid from a specific region and can increase the rate of interception of odorant molecules. We used hot-wire anemometry, high-speed videography and flow visualization to study air flow near the feathery olfactory antennae of male silkworm moths (Bombyx mori L.). When exposed to conspecific female sex pheromone, male B. mori flap their wings through a stroke angle of 90–110 ° at approximately 40 Hz without flying. This behavior generates an unsteady flow of air (mean speed 0.3–0.4 m s−1) towards the antennae from the front of the male. A pulse of peak air speed occurs at each wing upstroke. The Womersley number (characterizing the damping of pulsatile flow through the gaps between the sensory hairs on the antennae) is less than 1; hence, pulses of faster air (at 40 Hz) should move between sensory hairs. Calculation of flow through arrays of cylinders suggest that this wing fanning can increase the rate of interception of pheromone by the sensory hairs on the antennae by at least an order of magnitude beyond that in still air. Although wing fanning produces air flow relative to the antennae that is approximately 15 times faster than that generated by walking at top speed (0.023 m s−1), air flow through the gaps between the sensory hairs is approximately 560 times faster because a dramatic increase in the leakiness of the feathery antennae to air flow occurs at the air velocities produced by fanning.

Resurgence in bed bug infestations and widespread pesticide resistance have greatly renewed interest in the development of more sustainable, environmentally friendly methods to manage bed bugs. Historically, in Eastern Europe, bed bugs were entrapped by leaves from bean plants, which were then destroyed; this purely physical entrapment was related to microscopic hooked hairs (trichomes) on the leaf surfaces. Using scanning electron microscopy and videography, we documented the capture mechanism: the physical impaling of bed bug feet (tarsi) by these trichomes. This is distinct from a Velcro-like mechanism of non-piercing entanglement, which only momentarily holds the bug without sustained capture. Struggling, trapped bed bugs are impaled by trichomes on several legs and are unable to free themselves. Only specific, mechanically vulnerable locations on the bug tarsi are pierced by the trichomes, which are located at effective heights and orientations for bed bug entrapment despite a lack of any evolutionary association. Using bean leaves as templates, we microfabricated surfaces indistinguishable in geometry from the real leaves, including the trichomes, using polymers with material properties similar to plant cell walls. These synthetic surfaces snag the bed bugs temporarily but do not hinder their locomotion as effectively as real leaves.

Trains of 20-ms-duration pulses of pheromone were delivered at rates of 1–33 Hz to antennal preparations of males of Bombyx mori and Lymantria dispar, two moth species with bipectinate antennae. Resolution of rapidly pulsed plumes of pheromone was not compromised by a complex antennal morphology or by moderate changes in wind speed (25–50 cm/s). Fourier analysis of the electroantennograms resolved the temporal structure of the signal at frequencies up to 25 Hz for B. mori and up to 5 Hz for L. dispar. The ability of these sensory structures to identify the original (unchanged) frequency of the pulse train is particularly noteworthy because air is slowed by about an order of magnitude as it passes through bipectinate antennae. Although an unchanging frequency in slowed airflow may be counterintuitive, this flow pattern, and its effects on odorant patch shape and spacing, is explained from fluid mechanical principles (i.e., the principle of continuity). An unchanging frequency suggests that as decelerating air passes through a bipectinate antenna, the slowed patches of odorant are stretched, thinned, and brought closer together by the same factor with which they are slowed.