Does a falling ant die when she hits?
Why don't ants die when falling from a high distance?
Sharon, Moose Jaw, Canada
It’s a hot muggy day on the steep slopes of a Malaysian rainforest. About
60 feet (20 m) above the jungle floor, a small brownish-red acrobat ant clambers
out of a nest hidden under the whitish-gray bark of a macaranga tree.
Locking clawed back feet into the tree trunk , she follows an ant-laid
chemical trail down the trunk to forage for insects. A monkey hurtles past, brushing her off. Falling, the ant wildly splays her legs like a parachute to slow
her descent, and spirals downward, picking up speed. In less than a second, she
reaches terminal velocity, about 4 mph (6.4 km/hour), and falls at that speed until
she hits ground. She crawls away — unhurt — to search for a chemical path
back home, high above.
 Acrobat
tree ants in a Paraguay rainforest. Photo courtesy of Alex Wild, Copyright 2003, used
with permission.
How do ants fall such vast distances and survive? Easy. Two
factors save them:
- They have so little mass relative to their air resistance that they fall slowly and, therefore, have little
energy to dissipate when they hit.
- Their bodies are tiny deformable tanks, well designed to
absorb blows.
Falling slowly
Ants, like all objects falling through the atmosphere, have a terminal
velocity that depends on their shape, size, and mass. An ant picks up speed as
she falls through the air. The air, in turn, resists her movement with a force
proportional to the square of her speed. Eventually she reaches a speed at which the
upward drag forces exactly balance her downward weight and she stops
accelerating. That speed is her terminal velocity.
The terminal velocity of a small to medium ant is about 4 mph (6.4 km/hour),
according to the physics department of the University of Illinois. An
ant would fall faster, given a ball-like shape, but the ant's no dummy. She thrusts her legs out,
presenting more surface to the air, to fall slower, like a flat sheet of paper
instead of a balled-up sheet.
Indeed, a man has a terminal velocity of about 125 mph (200 km/hour) with arms
and legs fully extended to catch the wind like a parachute and about 200 mph (320
km/hour) when curled into
a ball. An ant slows similarly.
But, it isn't falling that hurts, it's the sudden stop. Hitting
ground, however, reaps the big benefits of falling slowly. When the ant
hits, she must dissipate her falling (kinetic) energy in order to halt.
That kinetic energy depends on the square of the velocity — not just
velocity. So she must dissipate much less energy on impact, than say a man
falling at a higher velocity. An ant goes 4 mph when she hits ---
about 1/30th times slower than a falling man on impact. She absorbs only
1/26,000,000th times (1/26 millionth) the energy of the man (assuming an ant weighs 1/10th of an
ounce (0.3 g) and a man 180 pounds (82 kg)). No wonder the man probably dies and
the ant walks away, unhurt.
"Sufficiently small animals cannot be hurt in a fall from any height: A
monkey is too big, a squirrel is on the edge, but a mouse is completely safe,"
says biologist
Michael C. LaBarbera
of the University of Chicago.
But an ant has even more advantages to survive falls. She isn't built
like a human.
Sturdy bodies
An insect's skeleton surrounds its body like armor. But, unlike a tank's
steel plating, an insect's armor is deformable to absorb and dissipate blows.
It is made up of several layers; the outer layer is made of a tough substance
called chitin (which is similar to the keratin that makes up our fingernails).
Even if impact with the ground rips a hole in the ant's exoskeleton, the ant
is unlikely to bleed much, because insect blood has excellent clotting
characteristics, says LaBarbera.
The nervous system is distributed throughout an ant's body, so the head can
take blows, unharmed, that would probably knock a vertebrate unconscious or kill
him.
Concrete ants and others
may well impact concrete, but as Meyers points out, not so tree ants. "An
ant falling 60 feet from a tree in the Malaysian rain forest is not likely to
hit its head on a concrete sidewalk. The forest floor of vegetation and
decaying leaves would make for a pretty soft landing!" emails entomologist
John Meyer,
professor at North Carolina State University.
The circulatory system is likewise distributed. An ant has a long
tube 'heart' that runs the length of her abdomen. The exoskeleton protects
the fragile tube from impact.
Finally, some ants glide!
Glider ants of the Amazon have adapted an ant's slow fall into a glide to
better survive the return trip.
When a glider ant falls from 100 feet (30 m), she
doesn't fall to the forest floor. Instead, she falls a little
bit, slows down, twists for a backward approach, swoops to the tree trunk (like
a kid on a rope swing), hits on the back of her armor-plated abdomen, and plunks
her clawed feet on the trunk — only about 30 feet (10 m) from where she started.
Had she fallen to the ground, how could she possibly find an ant-laid
chemical trail leading home among the litter? Worse: predators
abound. She'd be unhurt from the fall, but would die, nevertheless.
Almost certain death from predators is the major evolutionary driving mechanism behind the
gliding behavior, says insect ecologist Stephen P. Yanoviak of the University
of Texas Medical Branch in Galveston, the discoverer of such ants.
Further Reading:
The
biology of B_movie monsters by
Michael C. LaBarbera, University of Chicago,
Organismal Biology & Anatomy, Geophysical Sciences, the Committee on
Evolutionary Biology
Ant
behavior by Alex Wild, Myrmecos.net
The exoskeleton by John R. Meyer, North Carolina State University
Circulatory system of insects by John R. Meyer, North Carolina State
University
An ant dropped off the Empire State Building, physics department of the
University of Illinois
Gliding
ants by Stephen P. Yanoviak, University of Texas Medical Branch at Galveston
Amazing ants 'fly' when they fall by Robin Lloyd, Live Science
(Answered Jan. 12, 2009)
Comment
Comment
Readers' Comments:
- I recently was trying to capture or help a lizard who was trapped in my
house to get outside. It was at the top of a door leading to the back porch
and suddenly jumped and fell all the way down to the ground. It seemed to be
breathing heavily and I wondered and hoped it wasn't in pain or suffered
internal bleeding or something as a result. I know they can fall onto the
forest floor and not get hurt, but this was onto concrete. It actually
responded well, and climbed into the plastic box I was trying to use to
relocate it, and then I put it outside. Will it survive that fall?
Jessica gainesville florida, USA
- REPLY: Yes, it will survive the fall. The animal is light
enough to survive.
- Thank you so much. I didn't know that would apply to lizards as they
have no exoskeleton, but it's definitely smaller than a mouse. I've
heard stories of hamsters dying from falling off a table, though.
Interesting! _Jessica
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