Plankton
in the Sky?
Observing Aerial Plankton
Background
The American Heritage Dictionary defines plankton as "plant and animal
organisms, generally microscopic, that float or drift in great numbers in fresh
or salt water." But entomologists and people who study certain birds have
long known that some tiny insects and spiders drift through the sky in the
same way that plankton drifts in an ocean. These tiny bugs floating through
the air are called "aeroplankton" or "aerial plankton."
Ballooning Spiders Falling from the Sky
Dr.
Jerome Rovner, a leading arachnologist (authority on spiders), told Journey
North, "Ballooning spiders indeed make up a large component of the
aerial plankton. Darwin noted a mass landing of spiders on THE BEAGLE
when 200 miles off the coast of South America. About 15 or so years ago,
some Californians panicked at the sight of mysterious--and probably alien!--material
falling from the sky (the silk threads of a major spider ballooning event)."
How Many Airborne Insects and Spiders?
One
entomologist, Dr. Gilbert Waldbauer, calculated that during daylight
in May, a volume of air 1 mile square extending from 20 feet above the
ground to an altitude of 500 feet contained 32 million arthropods! He
wrote that "This amounts to 6 arthropods per 10 cubic yards of air.
Ten cubic yards is quite a small space, about the size of a small clothes
closet." Dr. Waldbauer adds that the number of airborne insects
and spiders decreases the higher up you go, and notes that the creatures
in aerial plankton at night are only about half as numerous as those
during day. You must wonder: Why would there be more insects and spiders
floating in the air during daytime than at night? Click
here for the answer!
Counting
Aerial Plankton
It's hard to identify the little creatures that make up aerial
plankton because they're so tiny. Scientists can collect them in traps
and sweep nets from airplanes. In 1926, the year before Charles Lindbergh
made his first famous flight across the Atlantic, some entomologists
at Tallulah, LA trapped insects in traps under the upper wing of a biplane!
Your class probably doesn't have access to an airplane, but there are
some ways you can observe aerial plankton. Enjoy the activities below
as you watch for ballooning spiders and other aerial plankton.
Try This! Viewing Aeroplankton
- View
at Night. Shine a flashlight into the dark sky and see what
flies and floats in its beam. You won't be able to identify
the specks,
but will gain an idea of how many "flying specks" there
are.
- View
in daylight. Set up an insect net on a pole near the ground. For
comparison at a slightly higher altitude, set up an insect net out
the second floor window or higher. Some school buildings have flat
roofs that are safe to walk on; an adult may be able to set up an
insect net on a pole on the roof. See what gets trapped inside! If
you live in a city with any very tall buildings, a fire tower, or
some other tall structure, the building superintendent may allow
setting up the net there for another sample from an even higher altitude.
- If you
don't have a very fine-woven insect net, try making one! Pantyhose
provides a good fabric fine enough to trap very tiny insects and
spiderlings. Use a stretched-out metal coat hanger for a rim, and
sew pieces of pantyhose together to make the net. Or you can use
a whole pair of pantyhose as a silly-looking but effective net by
rolling the waistband onto the hanger. That long net can trap a lot
of aerial plankton! Orient the net so it billows out when the wind
blows toward it. Then the wind will sweep insects and ballooning
spiders into the net. Write or draw to record what you find!
For More. . .
Just how far can "floating" spiders travel with their balloons? Read how Hawaii got its Happy Face spiders:
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