A FAMOUS estimate of the number of species on Earth could be a very long way off, according to a new study.

In 1982, Terry Erwin said that a rough estimate of the numbers of different plants, fungi and animals on our planet would be 30 million.

Andrew Hamilton of the University of Melbourne, Australia, has done some work on the subject and says that 5.5 million is more likely. The main problem for scientists in this area is finding the number of arthropods, the group that includes spiders and insects. Hamilton got his result by finding out how many different beetle species lived exclusively on certain trees in Papua New Guinea. He then scaled up his result for the whole planet and said that there are around three million species of arthropods.

Hamilton’s study is similar to the 1982 work, only much larger in size. This means that it will be more accurate, although the fact that it still only looked at one country is a big drawback.