Cats in 'chutes

As scientists we observe and try to explain, or we predict based on what we believe to be true.  Usually we do not get to see the results of our prediction or if we do it may be clouded with political agenda.  Well one of my most favorite stories in science cuts through all the waiting, all the politics, and comes as close to “proving” a concept as I know of. 

The main part of the story starts in the 1950’s on an island in the South Pacific called Borneo.  The natives there lived in huts with thatched roofs.  That means the roof of their house was made of dried vegetation like straw, reeds, rushes, and so on.  Of course they didn’t have doors or windows that closed tight so mosquitoes and other bugs and creepy-crawly things came in and out of their homes quite easily.

One advantage to living on an island is that it is easy to see the ecosystem pretty completely right before your eyes.  For example, there was a moth that laid its eggs on the thatch of the roof.  When the caterpillars hatched, they would eat the vegetation that made up the thatch.  This sounds like a bad thing, but there was also a wasp that laid its eggs IN the caterpillar, yes, inside the caterpillar.  When the eggs hatched and started to grow they killed the caterpillar.  This is the way nature works to keep things in balance.  Not all the caterpillars lived so they didn’t eat up the people’s houses.

A little plug for nature:  all this balance among the plants and animals went on for a long, long time before man came along to “take charge.”   But I digress…

Malaria is caused by a parasite that enters your body and begins to take over certain functions that you need to stay healthy—rather like a terrorist who invades your country and makes new rules.  The typical way that this malarial organism enters your body is through the bite of a mosquito.  The mosquito bites someone who has malaria, sucks up some of their blood which has the parasite in it.  When the mosquito bites you, the first thing it does is to “spit” some saliva into you to keep your blood from clotting while the mosquito sucks your blood out.  When it puts this anti-coagulant in, it also introduces that parasite it got from the other guy.

Well for some reason around 1950 more and more of the people of Borneo began to get malaria.  The World Health Organization (WHO), just two years old at the time, decided to step in and fix the problem.

Back in 1873, some scientists had put 14 carbon atoms together with 9 hydrogen atoms and 5 chlorine atoms in a very special way.  This new molecule looked like this

 and was called 1,1,1-trichloro-2,2-bis-(p-chlorophenyl) ethane.  Okay, that was too hard so they called it Dichlorodiphenyltrichloroethane.  By 1939, other scientists had discovered that it would kill insects—really kill them, really well!  By this time they knew that news people and marketing people would have to say the word so they just called it DDT.

DDT had become so popular in killing insects that it was used far and wide during World War II.  In fact, trucks used to drive down the beaches in the evening spraying this miracle chemical onto beach goers and in the air to keep mosquitoes away.  And it worked really well!

So, the WHO decided to spray the entire island of Borneo with DDT.  It was cheap, effective, and they would be heroes.

It worked.  Malaria cases dropped to almost zero.  HOWEVER…a while later the people of Borneo noticed their houses falling apart, and there were fewer cats, and more rats—a lot more rats, and people were getting bubonic plague spread by the fleas on the rats.

DDT works in an interesting way.  Rather than being broken down into smaller molecules and being eliminated from the body of something that it comes in contact with, DDT makes itself at home in cells of the organism.  When a larger organism eats several smaller organisms, it gets the doses of each of the organisms it ate added together.  When something higher up the chain eats it ingests the sum of all that organism ate and so on.  For example, a robin might eat many grasshoppers and a hawk might eat several robins and so on.  This is called biomagnification.

It seems that the wasp that laid its eggs in the caterpillars was killed by DDT, so the caterpillar population exploded and ate the people’s houses.  The roaches and other crawly insects were slowed or killed by the DDT and so the geckos caught and ate many more of them and the cats ate the geckos.  By this time there was enough DDT accumulation to kill the cats.  The rats flourished and the people got sick.

Now the amazing conclusion and punch line to this whole story.  What did the WHO do to solve the problem?

Illustration by Louise E. Klock

YES, drop cats in by parachute to control the rat population.  Eventually the effects of DDT began to wear off enough that the people could rebuild their huts, the cats lived and killed the rats, the people got better, and somebody at WHO got fired.

It would appear that the DDT was first consumed in small amounts by the insects and accumulated in sufficient quantity ultimately to kill mammals.  This supports the concept of biomagnification or the concentration of this poison as it moves up the food chain.  We thus have a real live experiment under ideal conditions culminating in the obvious conclusion that it is concentrated in tissues of living organisms.

In 1962, Rachel Carson wrote a book called The Silent Spring.  It is a book about a time when springtime comes but no birds come back because they have all died.  DDT keeps bird eggs from being solid enough for the birds to sit on them.  No baby birds, no singing in the spring—hence, the “silent” spring.  President John F. Kennedy read the book and began the work that led to the banning of DDT for use in the US in 1972. 

Take home message:  Rachel Carson planted the first seeds of the environmental movement in 1962 with publication of The Silent Spring.

Also, the cats were in crates which broke open when they hit the ground and released the cats…no, they did not each have their own parachute.

--klock