Buzzwords
Flea-flickers and football fields
May Berenbaum
I
don’t know who first came up with the
idea of measuring lengths in units of
football fields, but I imagine it was an entomologist. Football fields are the preferred
units for expressing equivalent distances that
insects, particularly fleas, could jump if they
were the size of a man. No sexist intent,
here; for some reason, these equivalencies
always seem to be measured with men in
mind. (My personal theory is that only a guy
would care if he could outjump a flea if he
were the same size as a flea.) Football fields
are routinely used to illustrate the prodigious
athletic capabilities of insects. According to
the standard text for introductory entomology, Borror, DeLong, and Triplehorn (1981),
“When it comes to jumping, many insects put
our best Olympic athletes to shame; many
grasshoppers can easily jump a distance of
1 meter, which would be comparable to a
man broad-jumping the length of a football
field.”
Information in the 1990 Guinness Book
of Records, proclaiming Pulex irritans the
“champion jumper among fleas,” reported,
“In one American experiment carried out
in 1910 a specimen allowed to leap at will
performed a long jump of 330 mm (13 in)
and a high jump of 197 mm (7.75 in) (pg
41).” These statistics in turn inspired some
calculations on the Bugman Bug Trivia
website (http://www.bugs.org/BUGQuiz/answers/flea_answer.shtml):
“So, let’s do the math... after scouring our extensive piles of resources, the best estimate
of flea length we could find was 1/16 to 1/8
of an inch. So let’s take the large estimate
(‘cause that’s more conservative). 1/8” is
about 3 mm. So, a flea can jump about
110 times its length. Now, for example,
if you are 5 feet tall (or long) and could
jump 110 times your length, you could
jump about 550 feet, which is about 183
yards or nearly 2 football fields!”
132
What was
that play again?
This flea-flicking
business has me
running in circles...
or is that jumping?!
I suppose these analogies are helpful to
sports fans, but I have no clear concept of
how long a football field is (having attending only one and a half football games in
my entire life, both of which took place
over thirty years ago). Moreover, “football
field” as a unit means different things in
different countries. As I understand it, Canadian football is played on a field that’s 110
yards long (which means that their football
fields have been larger than U.S. fields for
longer than their dollars have been). And
“football” in Europe refers to soccer and I
have no clue how long a European soccer
field is, nor whether European fleas make
the conversion. Admittedly, not all of the jump analogies
revolve around football. Whereas football
field units seem well suited to illustrate the
length of a flea’s broad jump, they would
seem far less useful to illustrate the relative
height of a flea jump. Indeed, more often
than not, jump-height equivalents are often measured in units of buildings, usually
relatively famous ones. The utility of such
comparisons depends on one’s familiarity
with scenic landmarks; in an article about
the Olympic prowess of animals, R. McNeill
Alexander references the apparently popular
comparison equating a flea’s 30-centimeter
jump to “a man jumping over St. Paul’s Cathedral” (Milius 2008), which for American
stay-at-homes is unenlightening at best.
But the football field as a unit of measure
is so firmly entrenched in the popular conscience that occasionally it serves as a unit
of height—e.g., at “Super bugs? Whimpy
[sic] humans?” (http://www.ftexploring.
com/think/superbugs_p1.html). “Fleas can
jump over 80 times their own height, the
equivalent of a 6 foot tall human jumping
over a building 480 feet (more than 1 and
a half football fields) high!” But short of
a seismic cataclysm, when can people see
football fields stacked vertically?
The problem with all of these calculations, of course, is that they fail to take into
account the surface area/volume ratio. Small
organisms, such as insects, live in a world
dominated by surface forces. The bigger the
organism, the greater is its volume (which
is a function of length times width times
height) relative to its surface area (which
is a function of length times width). Cubic
dimensions scale up faster than do squared
dimensions, so, as organisms increase in size,
American Entomologist • Fall 2008
American Entomologist • Volume 54, Number 3
but they can also, by slapping their jaws
against a hard object (such as an intruder)
or against the ground, propel themselves into
the air. The bouncer defense jumps, launched
off an intruder, can reach 40 cm horizontally,
and the escape jumps, launched from the
ground, cover shorter distances but greater
heights, up to 8 cm. Even more impressive
than the distances covered, though, is the
fashion in which they’re covered. They don’t
just slap their mandibles against a surface;
a stereotyped set of behaviors sends the ant
spinning head over all six heels, with a spin
rate that can peak at more than 60 revolutions per second.
One wonders what football analogy can
be used to place that feat in human terms. The
world record for “fastest spin on ice skates”
set by Natalia Kanounnikova at Rockefeller
Center in New York City, is 308 revolutions
per minute. During jumps, ice skaters can
reach 420 rpm, or about 7 revolutions per
second. But that’s about one-ninth the spin
rate of a trapjaw ant. Football players don’t
routinely spin, at least by design, but in terms
of spinning things on a football field, even
the football doesn’t measure up to a trapjaw
ant. Typically, a tossed football manages
about 8-10 revolutions per second, with an
acceleration of about 8 m/second. So, the
next time a football player is bragging about
his physical prowess, maybe a comparison
with the trapjaw ant will shut him up—but
even if it does, it’ll likely take longer than
100 nanoseconds.
References
Borror, D. J., D. M. DeLong, C.A. Triplehorn,
1981. An Introduction to the Study of Insects. New York: Holt, Rinehart & Winston.
McFarlan D, N. D. McWhirter, D. A. Boeh, 1990. Guinness Book of World Records. Sterling
Publishers.
Milius, S., 2008. Built for speed. Science News
174 (4): http://www.sciencenews.org/view/feature/id/34758/title/Built_for_Speed
Patek, S. N., J. E. Baio, B.L. Fisher, A.V. Suarez,
2006. Multifunctionality and mechanical
origins: Ballistic jaw propulsion in trap-jaw
ants. Proc. Natl. Acad. Sci. USA 103:12787
-12792.
May Berenbaum is a professor and head of the Department of Entomology,
University of Illinois, 320
Morrill Hall, 505 South
Goodwin Avenue, Urbana,
IL 61801. Currently, she
is studying the chemical
aspects of interaction between herbivorous
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surface area can’t keep pace with volume. Muscle strength increases with cross-sectional area, so a small organism (like a flea) has
muscles with a relatively high cross-sectional
area moving a relatively small volume. The
muscles themselves aren’t stronger—they’re
just doing smaller jobs relative to their size. A six-foot flea would have about the same
muscle strength as a six-foot man, so in all
probability, it wouldn’t be able to leap over
any goalposts unless they were knocked flat
and lying on the ground.
In fact, insect muscles might not even be
as strong as vertebrate muscles on an absolute basis. As the great twentieth-century
biologist J.B.S. Haldane famously wrote in
his essay “On Being the Right Size,”
“…the height to which an animal can jump
is more nearly independent of its size than
proportional to it. A flea can jump about
two feet, a man about five. To jump a given
height, if we neglect the resistance of air,
requires an expenditure of energy proportional to the jumper’s weight. But if the
jumping muscles form a constant fraction
of the animal’s body, the energy developed
per ounce of muscle is independent of the
size, provided it can be developed quickly
enough in the small animal. As a matter
of fact an insect’s muscles, although they
can contract more quickly than our own,
appear to be less efficient; as otherwise a
flea or grasshopper could rise six feet into
the air.”
Although insect muscles may be less efficient, they’re still capable of some amazing
feats. Some insects have muscles that function in ways unlike any muscles humans have
(or any other organism, for that matter).
Odontomachus bauri is one of a group of
ants collectively called trap-jaw ants; these
ants are capable of snapping their jaws shut
with incredible speed. Using an extremely
sophisticated high-speed camera recording
at 100,000 frames per second, my colleague Andy Suarez and his collaborators
measured, on average, closing speed ranging from 35.5 to 64.3 meters per second
and accelerations of 100,000 g (Patek et al.
2006). O. bauri can shut its mouth in less
than 100 nanoseconds. These investigators
also determined that the jaws exert a force
of 47 to 69 milliNewtons when they close,
which is approximately 370-500 times their
own body weight. The speed of the jaws
changes through the arc of closing, with the
mandibles slowing down past the midline,
possibly to reduce the risk of smashing them
if they hit each other. This spectacular mandibular prowess
raises the question as to why any organism
has a need to snap its jaws shut with such
force and speed. These remarkably versatile
ants can use their trapjaws to ensnare prey,
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