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06/05/2003
Scat Talk
After my last two columns on the presence, or not, of identical
twins in parallel universes, I felt it was time to pick a more
down-to-earth subject. One subject certainly qualifies. As U.S.
Fish and Wildlife employee Serena Rinker sang to a group,
including six children, gathered at the Loxahatchee Wildlife
Refuge in Florida, “It begins with an ‘S’ and ends with a ‘T’, it
comes out of you and it comes out of me, I know what you’re
thinking, but don’t say that, ’cause to be scientific we call it
scat.” I found this quote in a column by Steve Mirsky in the June
2003 issue of Scientific American titled appropriately “Dropping
By.” He didn’t reveal the tune to which the above lyrics were
sung.
Mirsky generally writes a lighthearted column and, given the
subject matter, this one was no exception. However, he did point
out that the study of scat is indeed a science and is a valuable
tool for obtaining information about the habits of past and
present animal life. The size, shape, color and content of scat
may provide critical information on the presence of certain
animal species in a given habitat as well and on its diet. For
example, fossilized scat, known as coprolite, contains the
remains of meals eaten by dinosaurs more than 60 million years
ago. Whereas some of the huge creatures were vegetarians,
except for the insects inadvertently ingested, Tyrannosaurus rex
loved feasting on other dinosaurs if given the chance. Coprolite,
incidentally, is also reportedly a treasured collectible for some
scat devotees. I suspect that fossilization removes some of the
objectionable characteristics of more recent scat.
What about scat disposal? We in the industrialized nations have
developed quite extensive and sophisticated systems for the
distribution and removal of scat from our water supply systems.
In some countries, human scat has been used as fertilizer. In my
younger days, I’ve used scat in the form of horse manure, dried
and bagged in a commercial product, to fertilize my vegetable
garden. Scat known as dung is still used as a building material
and I believe as a fuel in some more primitive societies.
In searching for more information on the disposal of scat, I came
across a May 16, 2003 article on the National Geographic News
Web site nationalgeographic.com. The article by John Pickrell
was titled “Scat-Firing Caterpillars Elude Predators”. The insect
in question is the skipper butterfly caterpillar, in particular the
silver-spotted skipper, perhaps more familiar to you as
Epargyreus clarus. Let’s call it Skipper for short.
Skipper has the remarkable ability to eject its pellets of its scat,
frass, over a distance as far as 5 feet, or roughly 40 times its
length. Pickrell, in a somewhat distasteful calculation, concludes
that this would be equivalent to a 6-foot human about expelling
his scat roughly as far as from home plate to the left field wall in
the old Polo Grounds. (Pickrell says 240 feet; the sports analogy
is my own doing.) At any rate, Skipper’s feat is certainly one
that should not go unrecognized.
Why would Skipper be so fastidious as to want to distance its
waste from its vicinity so far away? Other animals tend to
dispose of their scat for the same reason we do – it’s good
hygiene. One example given in the Geographic article may
answer a question that I’ve pondered for over 50 years. When
my wife and I were married we moved into a garden apartment
in Parma, Ohio. We were married in January and, that spring,
two robins built their nest on the windowsill outside our
bedroom. Baby robins arrived and we had a close-up view of the
whole scene. I was surprised to observe that, when the parent
fed the baby robins a worm, the baby would promptly raise its
bottom and emit a pellet of scat. It was like clockwork. But
what really shocked me was that the parent would quickly eat the
scat!
Or so I’ve thought all these years. However, Pickrell states that
some nestling birds enclose their scat in mucilage-coated sacs for
convenient disposal by the mother or father bird. Were our
robins surreptitiously flicking away the scat pellets or just storing
them to dispose of in flight? I probably will never know the
answer.
But back to Skipper and ecologist Martha Weiss of Georgetown
University. She laments the fact that ecological research has
been heavily devoted to studies of foraging, while defecation has
received much less attention. Her concern is answering the
question of why Skipper’s long-range scat ejection evolved in the
first place. Skipper’s unusual ability also captured the attention
of Stanley Caveney at the University of Western Ontario in
Canada. He was more concerned with the mechanism of the
ejection. Caveney found that the “scatapulting” mechanism
involved a pumping up of Skipper’s blood pressure under what
might be termed the anal launch pad. He likens the launching to
the flicking of a pea.
Having nailed down the mechanics of the scat launch, let’s
address its purpose. It doesn’t seem that such scatapulting is
necessary for hygienic purposes. Indeed, some caterpillar
species like to climb on silken strands decorated with pellets of
scat (frass). The scat pellets help to protect these caterpillars
from ants. Why would Skipper, who lives in a silk-stitched leaf
nest, not want to employ the same tactic?
The answer lies in the fact that Skipper seems to fear the
predatory ambitions of a species of wasp, not the ant. The
skippers form a leaf nest by folding the leaf and anchoring the
folded nest with silken threads. Weiss did a clever experiment in
which she placed the leaf nests of silver-spotted skipper
caterpillars into paper wasp colonies. The skipper nests were
roomy affairs in which Weiss hid either scat pellets or black
beads that resembled the pellets. Some 70 percent of the wasps
visiting the skipper nests spent their time in the nests with the
scat. When skipper larvae were added to both types of leaf nests,
the wasps chomped down on 5 times as many larvae in the scat
nests as in the black bead nests.
The conclusion then is that Skipper fires off his scat to help
avoid the wasps, which seem attracted by the odor of the scat.
To rule out that hygiene might still be the dominant reason,
Weiss tried raising skippers in nests to which 30 days worth of
scat was added. Without any wasps around, the skippers grew up
to be as healthy as did skippers raised in a scat-free environment.
This experiment certainly seems to show that hygiene plays no
role.
The finding that the odor of scat attracts certain predators would
also explain the fact that many distantly related kinds of
caterpillars have also developed a scat firing capability. Another
example of the ever-evolving battle of prey versus predator.
So much for frass, dung, manure, coprolite or whatever the term
you prefer for scat. Best to leave that other word for such
occasions as when you’ve missed a one-foot putt or put a third
golf ball into the pond on the 17th at Spooky Brook. Been there,
done that!
Allen F. Bortrum
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