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Thatch-eating Caterpillars
Home Thatch-eating caterpillars ruined roofs DDT was the cause of the deaths of cats in Borneo A “cat-drop” occurred to replenish the cat population
  An article by a researcher for the WHO in The Bulletin of the World Health Organization (Cheng 1963, see reference below) confirms the thatch-eating-caterpillars feature of the story. After insecticide spraying to eradicate malaria was conducted by teams organized by the WHO, complaints were made by representatives of areas in Sabah and Sarawak (see map) during a conference on malaria because the spraying caused the deterioration of the thatched roofs of the buildings in those areas. As mentioned in the story, Cheng states that the reason was because the moth larvae (caterpillars) somehow avoided DDT whereas their parasite, a small chalcid wasp which injected their larvae into the caterpillars, was highly susceptible to the DDT causing their decline and the subsequent increase in caterpillar numbers. What is not stated in the cat story but related in this report is that a population study of the caterpillars in villages located in Sabah determined that DDT spraying caused a 50% increase in caterpillars per roof area over that of the normal population, but the huts sprayed with a more toxic insecticide, dieldrin, had almost no caterpillars. Oddly, then, there would have been no complaints of this sort had the more toxic insecticide been used everywhere, thus killing both moth caterpillar and wasp. Also, it is likely that versions of the cat story that contain North Borneo (Sabah) as the place, and dieldrin as the insecticide, are linked to this study.

A literature search to determine where DDT and dieldrin were used in Sarawak and Sabah resulted in several relevant articles. A report was written by the members of the WHO anti-malarial team working in Sarawak (de Zulueta and LaChance 1956). Their report describes the first efforts to spray DDT and another insecticide, BHC, in Sarawak to prevent malaria between 1952 and 1955. In essence, spraying only occurred inside dwellings, which for each village, consisted of one structure, or “longhouse”, a large thatched-roof building that could house as many as 100 families. This living arrangement was advantageous for the eradication of malaria as it meant that spraying could be localized unlike areas where people lived a nomadic or semi-nomadic existence. The report also describes the spraying technique used: DDT was mixed as a 75% solution in water and applied on walls and under beds at the rate of 2 g/m2 twice a year. This application rate was high enough to form white spots of DDT residue on surfaces (Sandosham 1959). Colbourne et al. (1960) also add that dieldrin was first used in Sarawak in 1955 because its higher toxicity required less volume to be transported through the jungles of Sarawak. According to Colbourne et al., dieldrin was used throughout “the First Division” of Sarawak, but because of its higher cost and toxicity, its use was discontinued, presumably at the end of the spraying effort in 1957. For administrative purposes, Sarawak was divided into five divisions of unequal area numbered one to five from west to east across Sarawak (Morrison 1993). Therefore dieldrin was primarily used in the westernmost part of the state which includes the capital, Kuching (Figure 1). Detailed reports on the anti-malarial program in Sabah similar to those provided by de Zulueta and LaChance (1956) and Colbourne et al. (1960) for Sarawak could not be found. However, in an analysis of the program in certain parts of Sabah, Cheng (1967) states that DDT was “the residual insecticide in use in the programme.”

The island of Borneo showing the Malaysian states of Sarawak and Sabah, and the location of the village of Bario, Sarawak. (http://commons.wikimedia.org/wiki/Image:Borneo_blank_map.svg)


  • Cheng FY. 1963. Deterioration of thatch roofs by moth larvae after house spraying in the course of a malaria eradication programme in North Borneo. Bulletin of the World Health Organization. 28:136-7.
  • Colbourne MJ, Huehne WH, Lachance F de S. 1960. The Sarawak anti-malaria project. The Sarawak Museum Journal 9:215-248.
  • de Zulueta J, LaChance F. 1956. A malaria-control experiment in the interior of Borneo. Bulletin of the World Health Organization. 15:673-693.
  • Sandosham AA. 1959. Malariology with special reference to Malaya. Singapore: University of Malaya Press.
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