the truth about Hamadryas (Re: Crackers)

[Doug Yanega]

>from The Butterflies of North America by James A. Scott, Stanford
>University Press, Stanford, California, 1986 (there is info on 8 species
>of Cracker - may be in a local library)
>under Gray Cracker (Hamadryas februa): "Hamadryas adults land upside down
>with the barklike wings flattened against tree trunks for camouflage. To
>await females, males perch on trees and dart out at passing butterflies,
>insects, even people, often making a "cracking" sound with the abdomen.
>Males of all Hamadryas species - except perhaps H. atlantis and H.
>iphthime, which are poorly studied - share this behaviour, which males
>evidently use to discriminate males from females (males may pursue only
>non-cracking adults), and which accounts for their common name. Hamdryas
>males have two long lateral spiny rods extending backward from abdomen
>segment 8, which probably produce the cracking sound when the valvae twang
>the rods (using a spiny dorsal part of the valva; the spiny parts and rods
>are longer in species that often crack). The sounds are produced only in
>flight, for unknown reasons. Both sexes have tympana on the under forewing
>base, which S. Swihart proved detect sound but cannot produce it."

James A. Scott is completely wrong, and it's tragic that the nonsense above
is in print and will be cited for centuries to come as if it were true. I
don't know if Scott started it, but he certainly propagated it to many
people.

REALITY: There are swollen veins on the costal edge of the male forewings,
and if the males hyperextend during their wing strokes, the wing edges
strike one another at the top of the upstroke and make a loud "clack". The
species that do not clack do not have the swollen veins, only males have
the swellings, and they can only make sounds while in flight. They can
clack even if the abdominal apex is removed. If you hold a male Hamadryas
in such a way as to allow it to flap its wings freely, they will clack for
you, but if you hold a piece if tissue paper vertically above the body so
it comes between the wings on the upstroke, the clacking is stopped. You
can turn the clacking sound on and off by raising and lowering the tissue
from between the wings. I have performed this experiment myself to confirm
it. The percussive nature of the sound production mechanism has been
documented in the literature, but evidently more people in the US read
Scott than read scientific journals.

Argh.


Doug Yanega        Dept. of Entomology         Entomology Research Museum
Univ. of California - Riverside, Riverside, CA 92521
phone: (909) 787-4315 (standard disclaimer: opinions are mine, not UCR's)
           http://entmuseum9.ucr.edu/staff/yanega.html
  "There are some enterprises in which a careful disorderliness
        is the true method" - Herman Melville, Moby Dick, Chap. 82



 
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