Worlds of David Darling > Children's
Encyclopedia of Science > Spiderwebs to Skyscrapers > Chapter 6
SPIDERWEBS TO SKYSCRAPERS:
The Science of Structures
a book in the eXperiment! series by David Darling
6. Home Grown
Many of the world's most amazing structures are not made by human beings
at all. Termites, for example, build tall towers of mud and saliva, a mixture
that sets hard as concrete. Rising up to twenty feet high, these towers
provide ventilation for the main nest, which is below ground level.
Spiders build webs from a silky substance than is stronger than steel if
stretched out to the same thickness. In fact, at an army research center
near Boston, scientists are trying to develop superstrong lightweight fibers
based on spiders' silk. These could be used, for example, in parachutes
or bullet-proof clothing. We can learn much from the structures and building
materials of animals and plants.
Webs: A Fly's-Eye View
You will need:
- A magnifying glass
- A microscope and clean slide
- A spider's web
What to do:
Find a spider's web and examine it carefully with the magnifying glass.
Sketch or describe any features you can see on the strands. If possible,
identify the type of spider that made the web.
Place the slide behind a section of the web and lift it away so that
one or two strands stick to the middle of the glass. Put the slide
under the lowest power of the microscope. Make a careful sketch of
what you see. Do some strands of this web appear different than others?
Increase the magnification and see if this brings any more detail
Repeat these observations with webs made by other kinds of spiders.
The webs of spiders work in two main ways. Some webs have "capture" threads
that are covered with small sticky droplets to ensnare prey. Other webs,
built by a different family of spiders, are dry. These dry webs consist
of a fuzz of fine threads with loops and barbs for holding on to their victims.
The Master Builder
The largest and most spectacular animal constructions are the dams and lodges
built by beavers in North America. The beaver's long front teeth grow throughout
its life and are kept to a manageable length by gnawing at the trunks and
branches of trees. A beaver can fell a tree three feet thick. It floats
the wood down the river to the site where the dam is to be built. The animal
carries mud and stones in its forepaws and adds them to the branches to
form the dam wall.
|Activity in and around a beaver
Some distance behind the dam, in the lake that has been formed, the beavers
build a dome-shaped "lodge." This provides a warm, safe shelter for one
or more family groups. The entrances are underwater so that they remain
open even when the surface is frozen over in winter.
Beavers can strip the lake shore of all trees to a distance of several hundred
yards. When they have done this, they simply move on to a new site. Eventually,
the old site becomes clogged with mud. New vegetation then grows on the
rich soil created by the beavers' building.
Make Like a Bird
You will need:
- An abandoned bird's nest
- Rubber gloves
- Several sheets of paper
- Measuring scales
- Various materials for building your own nest, such as twigs,
feathers, and mud
What to do:
Make sure that the bird's nest is no longer in use before you touch
or remove it. Use rubber gloves if you wish, since the nest is likely
to contain various bugs. Weigh the whole nest. Observe closely how
it has been made. How does it hold itself together? How have the various
materials been used in its construction? Carefully pull the nest apart
over a sheet of paper and sort the contents into piles – twigs
on one sheet of paper, feathers on another, and so on. Weigh the various
piles and work out what percentage each represents of the total weight
of the nest.
|An American robin's
Now attempt to make your own nest from scratch. Can you equal or improve
on the bird's design? Remember, only use building materials that would
be available to the bird, though these could include human-made articles
that have been thrown out.