Nature's Engineers

Birds build nests to keep their eggs safe and warm and to give their young a place to live until they can take care of themselves. Nests are built out of a variety of materials, including sticks, grass, string, paper, and pine needles. Usually the outer part of the nest is made of larger, more loosely-woven materials; the inner part is made of finer, more tightly-woven materials. Some birds cement the nest together with mud or sticky saliva; others bond the nest with tent caterpillar silk and spider webs. Certain birds camouflage and protect the nest by covering it with a dome or roof. Building a nest can take anywhere from a few days to a few weeks depending on its complexity.

Ants are social insects. They live in colonies, some numbering more than a million ants. With numbers like that, ants need a structure which combines an apartment building, a grocery store, and a daycare. To meet their structural needs, some ants build huge hills out of sticks and dirt. These mounds often extend underground to vast tunnels and galleries.

Inside the hill, ants bring food to their queen. She lays eggs which other ants care for in nurseries. Some ant species live on fungi which they plant, grow, and take care of in underground galleries. Others build chambers in their nests using a paper-like substance made of chewed-up plant material.

Beavers like to swim around in ponds and lakes. If there isn't a pond or lake available, beavers have the structural know-how to build their own. They use the same methods to build dams as we do.

Beavers make a dam foundation by wedging large branches or logs into the bottom of the stream bed. Next they add layers of branches, held together with mud, rocks, and loose vegetation. A coating of mud seals the structure.

Beavers build lodges in which to live and raise young. Tree trunks, branches, and vegetation are woven together and coated with mud to make a solid structure. Beavers then chew or dig tunnels and rooms inside the cone-shaped lodges.

Not all spiders spin huge webs to trap their prey, but these are the most noticeable spider structures. Spiders build webs from silk produced in their abdomen. The average garden spider makes a web with a total thread length of 20 to 60 metres. During the web-building process, the spider continually makes adjustments so stresses are spread evenly across the threads. Some spiders run as many as 80 threads radiating out from the centre of the web. The angles between the threads are usually the same--the garden spider places its threads about 15 to 20 degrees apart. A spider may build as many as 100 webs in its lifetime; each weighing less than a milligram.

Spider silk may seem weak to us, but it is stronger than a piece of steel of the same size. If a spider were the same size as a human, it would be able to spin a web strong enough to catch a helicopter!

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