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Hobby Forum Index » Animals and Wildlife » Mitton: Blister beetles bleed defensively - Some...
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 Posted: Sat Sep 06, 2008 4:09 am |
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http://www.dailycamera.com/news/2008/sep/04/mitton-blister-beetles-bleed-defensively/
Mitton: Blister beetles bleed defensively
Natural Selections
By Jeff Mitton (Contact)
Thursday, September 4, 2008
The monsoon brought out the blooms on the desert four o’clocks,
Mirabilis multiflora, and the Rocky Mountain bee plants, Cleome
serrulata, near Crownpoint on the Navajo Nation. The floral flush
attracted a legion of large, slow, clumsy beetles with an ominous
presence.
Black and red lined blister beetles, Megetra vittata, are plump, more
than an inch long and incapable of flying or running. They do not flee
from predators, but deter them with aposematic or warning coloration:
brilliant red bands on a shiny black background.
More than 2,000 species of blister beetles are adequately defended by
the compound cantharidin. When a predator threatens them, they do not
bite, sting or spray, but they reflexively bleed from their knee
joints. Their blood contains low levels of cantharidin, sufficient to
deter most predators.
Cantharidin applied to human skin quickly produces large, fluid-filled
blisters that take weeks to heal. Some humans have been inadvertently
poisoned by eating frog legs or geese shortly after the animals had
feasted on blister beetles. Moderate amounts are lethal, and small
amounts produce abdominal pains, extreme thirst, muscle weakness, low
pulse rate and lowered blood pressure. Men suffer painful urination
and long-lasting, painful arousal.
The physiological effects of cantharidin have been known for thousands
of years; Hippocrates prescribed it to his patients more than 2,000
years ago. This toxic compound, colloquially referred to as
Spanishfly, has been used as an aphrodisiac, often with tragic
consequences. For example, the Roman poet Lucretius is believed to
have died of cantharidin poisoning after using it as a love potion.
Recently, numerous horses have died after eating hay containing
blister beetles, and chickens have died after eating blister beetles.
Although cantharidin defends all blister beetles, it is produced only
by males. During mating, the male passes not only his genes but also
substantial amounts of cantharidin to the female. Some cantharidin is
stored in her tissues, but most of it is incorporated in her eggs.
Insects specializing on egg predation will eschew eggs tainted with
cantharidin.
Cantharidin’s protection of eggs is so effective that it has been
adopted by species that cannot synthesize it. The entomologist Thomas
Eisner studied the black and orange beetle, Neopyrochroa flabellata,
which is attracted to and driven to consume cantharidin. When a
blister beetle dies, black and orange beetles lick cantharidin from
the carcass. However, only male black and orange beetles indulge in
cantharidin feeding.
Male black and orange beetles court avidly, but females will accept
the advances of some males while rejecting others. Eisner determined
that females preferentially accepted males emanating cantharidin’s
perfume. Like black and red blister beetles, black and orange beetles
pass cantharidin to the female with their genes. And like female
blister beetles, female black and orange females invest most of their
nuptial cantharidin in their eggs. Females choose the males who will
provide an effective chemical defense for their eggs.
When I first encountered the ponderous black and red lined blister
beetles, I knew nothing about them, but I sensed that they were
dangerous. Like skunks and porcupines, they were incapable of fleeing
from predators because an effective defense makes flight unnecessary. |
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