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or ... The Effects of Humans on a Specific Food Web

A food web is all of the feeding relationships in an ecosystem. A food web is a complex and interconnected unit. This becomes clear to us when human actions have unexpected effects. An example of this is evident in the events on the Southeast Asian island of Borneo. In 1955, the World Health Organization used the pesticide DDT to kill mosquitoes that carry the disease malaria. Malaria is a disease of red blood cells. Severe fever and sweats characterize it. The DDT killed the mosquitoes and relieved the malaria but it caused an undesirable chain reaction on the island.


First, the island homes thatch roofs started collapsing. What could this have to do with DDT? The DDT had not only killed the mosquitoes but also wasps that ate thatch-eating caterpillars. Without the wasps, the caterpillars multiplied and devoured the thatch roofs.


Second, the DDT was killing cockroaches as well as mosquitoes and wasps. Island lizards then ate the cockroaches. The pesticide in the cockroaches damaged the lizards nervous system. When one part of the web was disturbed other parts were affected. The effect was that the lizards movement and reflexes slowed. Because they moved so slowly, most of them were caught and eaten by house cats. After they ate the lizards, the cats suffered the effects of the DDT and died in great numbers.


Without cats in the village rats from the forest moved in. The rat’s fur carried fleas. The fleas were infected with the bacteria that cause the plague. Plague is a devastating disease that can cause mass mortality. Finally, officials were forced to parachute crates of healthy cats into Borneo to control the rat population and rid the island of plague.

The chain of events on Borneo occurred because the organisms on Borneo were connected to each other in a food web. When one part of the web was disturbed, other parts were affected.


  1. How would you describe the effect that DDT had on the island of Borneo in 1955?
  2. What would you advise the island residents to do differently if they have a similar problem in the future?
  3. How could this story help us know how to deal with the world around us?
  4. Should DDT be used anywhere on Earth?
    • Explain why you made this decision.
  5. How were the animals in the story interconnected?
  6. What could happen where you live that is similar to this story?
Research the events described above and then answer the following question. What are some other methods that the residents of Borneo have used to solve its mosquito problem?

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Updated October 24, 2008 by: Glen Westbroek

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