Ecology is the science of the interactions of organisms in their natural environment. This field of study has developed over the past four decades since its genesis in the early 1960’s when an awareness of the large-scale impact of mankind’s activities on the environment first became apparent. The early ecologists emphasized the need to understand the myriad interconnections that link the various forms of life in even “simple” ecological settings such as a pond or desert area. Awareness of these interconnections, they often wrote, comes as a consequence of mankind’s interference in some aspect of these “food webs” that result in unforeseen negative outcomes. One of the most often-told events of this sort involves a situation in Borneo that has become famous not so much for how it illustrates the unintended disruption of closely linked organisms as for the bizarre nature of the solution proposed. A typical example is given below and found on the web [Click Here].

“In the early 1950s, there was an outbreak of a serious disease called malaria amongst the Dayak people in Borneo. The World Health Organization tried to solve the problem. They sprayed large amounts of a chemical called DDT to kill the mosquitoes that carried the malaria. The mosquitoes died and there was less malaria. That was good. However, there were side effects. One of the first effects was that the roofs of people's houses began to fall down on their heads. It turned out that the DDT was also killing a parasitic wasp that ate thatch-eating caterpillars. Without the wasps to eat them, there were more and more thatch-eating caterpillars. Worse than that, the insects that died from being poisoned by DDT were eaten by gecko lizards, which were then eaten by cats. The cats started to die, the rats flourished, and the people were threatened by outbreaks of two new serious diseases carried by the rats, sylvatic plague and typhus. To cope with these problems, which it had itself created, the World Health Organization had to parachute live cats into Borneo.”

Detail of drawing in “Operation Cat Drop” (Harrison, 1965)

Other versions of the “cat story” can be found here.

These versions include:

• The plague and typhus actually did break out
• The cats were parachuted by the Royal Air Force
• 14,000 cats were parachuted
• The United States was involved
• Planes sprayed the DDT

The wide range of variations of the story suggests the making of a modern myth; a story containing some essence of truth but embellished to emphasize an underlying theme. Therefore, a search was conducted to determine the truth of the various aspects of the story, in particular whether:

• 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

The details of the literature review of this story are given in the links above but below are the essential results of the review:

• DDT was sprayed to reduce malaria in Borneo
• “thatch-eating” caterpillars did manage to avoid the DDT and proliferated with the result of enhancing the decay of thatch-roofed by this means
• DDT caused the death of cats in some areas where DDT was sprayed indoors. However, the deaths were caused by direct ingestion of the DDT when the cats licked their fur contaminated with DDT and, therefore, the deaths were not caused by the biomagnification of DDT through a food chain as suggested in the cat story.
• A “cat drop” did occur to replenish a cat population in Borneo. The only written evidence for this states that the drop occurred in one remote village of northern Borneo, Bario, in the Malaysian state of Sarawak. A number in excess of 20 cats were dropped in a special container designed to withstand the parachute drop by a large transport plane operated by the Royal Air Force.

Given the facts found, a revised version of the cat story is offered:

As part of anti-malarial campaign in the northern states of the island of Borneo in the late 1950’s, the World Health Organization sprayed DDT and other insecticides to kill the mosquito vector for malaria. During this campaign, DDT was sprayed in large amounts on the inside walls and ceilings of the large “long houses” that housed an entire village in these areas. As a consequence of this effort, the incidence of malaria in the region fell dramatically. However, there were two unintended consequences of this action. There was an increase in the rate of decay of the thatched roofs covering the long houses because a moth caterpillar that ingests the thatch avoided the DDT but their parasite, the larvae of a small wasp, did not. Also, the domestic cats roaming through the houses were poisoned by the DDT as a consequence of rubbing against the walls and then licking the insecticide off their fur. In some villages, the loss of cats allowed rats to enter, which raised concerns of rodent-related diseases such as typhus and the plague. To rectify this problem in one remote village, several dozen cats were collected in coastal towns and parachuted by the Royal Air Force in a special container to replace those killed by the insecticides.

This version of the story indicates that there were certainly unintended consequences associated with spraying DDT to control malaria, however the aspect of the original that made it an often-repeated ecological tale is now missing. There is no evidence to suggest that the cats died via biomagnification of DDT through a food chain and so this important aspect of the original story is now missing. So how did this aspect of the story originate?  Certainly, it is suggested by Tom Harrisson in his original account of the story (see links above for all references). However, Harrison did not write his account of the cat drop until five years after the event took place in early 1960. Meanwhile, in the interim year of 1962, Rachel Carson’s Silent Spring was published. It is therefore possible that, being a conservationist, Harrisson likely read the book, realized his association with a DDT-related event, and naively ascribed the cat deaths in the area of Bario to the biomagnification of DDT in the manner explained by Carson. Gordon Conway then accepted that explanation and added the factual information concerning the thatched-roofs. Gordon Harrisson then related the story in a popular nature magazine, Natural History, in 1968 without naming Conway or Harrisson, and therefore broke the link to Harrisson as the source. The story then became the most famous, and only found, example of mammalian deaths due to the biomagnification of DDT.

Prepared by:

Patrick T. O’Shaughnessy

An associate professor at the University of Iowa in Iowa City, Iowa.