Brief comm 20/1/00 mx

brief communications
NATURE
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VOL 403
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20 JANUARY 1999
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www.nature.com
265
Ultrasonic hearing in nocturnal butterflies
Hedylids have ultrasound-sensitive ears on their wings to help them avoid bats.
Figure 1 Hedylid butterflies have ultrasound-sensitive ears that allow them to evade bats in flight. a, Lateral view of 
M. heliconiaria,
showing the location of the right ear. An arrow points down the canal to the tympanic cavity where the tympanic membrane (not shown)
resides. Scale bar, ~3 mm. b, Scanning electron micrograph of the right tympanic cavity showing the tympanic membrane (TM), ear
canal (Ca) and an accessory membrane, the conjunctivum (Cj). Scale bar, 120 
mm. c, Consecutive video images (41 frames at 30 frames
per s; 13 before and 28 after the stimulus onset) of a free-flying 
M. heliconiaria responding to a short (~250 ms), high-frequency (25
kHz), high-intensity (
¤100 dB) sound. Arrow, flight direction; arrowhead, stimulus onset.
Figure 2 The presence of hearing
mapped onto a lepidopteran phy-
logeny
10
. Ultrasound-sensitive ears
occur on a variety of body parts
(arrowheads) reflecting multiple
evolutionary origins. All ears,
known to function primarily as bat-
detectors, occur within the Obtec-
tomera. We propose that hearing in
extant Lepidoptera originated as a
response to selection pressures
imposed by echolocating bats in
the late Palaeocene, and that
echolocating bats were a driving
force for the large, species-rich
butterfly groups Hesperoidea and
Papilionoidea (Sun symbol) to move
into the daytime. The butterfly
superfamilies are highlighted in
bold. Earlessness and nocturnalism
are the plesiomorphic (ancestral)
characteristics of the Lepidoptera.