Performance Analysis of Ormia Ochracea's Coupled Ears


To perpetuate its species, the female Ormia ochracea, a parasitoid fly (Fig. 1), must find a male field cricket using the cricket's mating call. The Ormia has a remarkable ability to locate these crickets very accurately using binaural (two-ear) cues (interaural differences in intensity and arrival time from an incident acoustic wave). This is unexpected as the distance between the ears of the fly (about 1.2 mm) is much smaller than the wavelength of the cricket's sound call. Hence, the resulting cues are extremely weak to be detectable by the central nervous system of the fly. Experimental research in [1] explains that this ability arises from the mechanical coupling between the Ormia's ears (Fig. 2(a)), modeled as a system consisting of spring and dashpots (Fig. 2(b)). The Ormia's ears are located behind the head and under the neck (Fig. 2(a)).


Fig. 1: Left: A picture of the Ormia Ochracea (source), Right: Parasitoid fly Ormia ochracea and its Cricket host (source).

A female O. ochracea on a spherical treadmill (click here if you cannot see the movie). (Source)
To evaluate the accuracy of its direction finding abilities, a female O. ochracea was tethered on a
spherical treadmill, attached to a moveable speaker. The speaker simulated cricket chirps. The
experimental error in the female O. ochracea's direction finding was measured as 2 degrees.

Our Research
  • We analyzed the localization accuracy of the O. ochracea's coupled ear system using a statistical approach.
  • We first transformed the mechanical model of the coupled ears to impulse and frequency responses.
  • We illustrated that the coupling magnifies the time and amplitude differences between the received signals on two ears [2].
  • We then converted the mechanical model to a statistical one and analyzed the localization accuracy by computing the Cramer-Rao bound (CRB) (Fig. 3).
  • Using the bound results, we showed quantitatively that the coupling improves the accuracy of direction of arrival (DOA) estimation in the presence of interference and noise (Fig. 3).
  • For our research on Ormia inspired coupled beampattern design, click here.

Fig. 2: (a) Anatomy of the female Ormia ochracea's ear. Top: side view of the fly. Bottom: front view of the ear after the head was removed.
(b) Top: front view of the ear after the head was removed. Bottom: mechanical model[1].

Fig. 3: Square-root of Cramer-Rao bound on direction of arrival estimation vs. SNR. Here M refers
to the number of sources (crickets). The number of time samples is 2000, corresponding to 40 ms.

  1. R. N. Miles, D. Robert, and R. R. Hoy, "Mechanically coupled ears for directional hearing in the parasitoid fly Ormia ochracea," J. Acoust. Soc. Am., vol. 98, no. 6, pp. 3059-3070, 1995.
  2. M. Akcakaya and A. Nehorai, "Performance analysis of the Ormia Ochracea's coupled ears," The Journal of the Acoustical Society of America, Vol. 124, pp. 2100-2105, Oct. 2008.