|MadSci Network: Zoology|
How many species of insects are there in the world?
You are right, this is a question virtually impossible to answer.
The main difficulties are:
1.) by far not all species are discovered,
2.) it takes enormous amounts of time to describe new species and compare them with known ones and,
3.) no species is static - there are always adaptations, variations, and regional differences. It is thus difficult to define a species.
What do we know?
According to different authors we have identified 700000 to 900000 species of insects. In the following I use figures given by EO Wilson:
All organisms (plants, bacteria, fungi, animals...) total species known: 1413000 total species on earth: 10 to 100 million new species described each year currently > 10000
total species known 1032000
total species known 751000
EO Wilson again cites Erwin for an estimation of arthropods in the
tropical forests world-wide:
Examining one species of trees (Luehea seemannii) Erwin found 163 species of beetles living exclusively in the canopy of this one species. There are 50000 tropical tree species known. If the situation on Luehea seemannii is typical there should be more than 8 million beetle species.The beetles had been 40% of all arthropods found. If that proportion is typical there should be more than 20 million arthropods. There are about twice as many arthropod species in the rain-forest canopy as on the ground therefore the total number of arthropods should be greater than 30 million.
The number of insect species outside the tropics is negligibly small so that is also the estimation for the world.
It is absolutely clear that the assumptions Erwin made are not proven. Changing these assumptions would lead to totally different figures. For example Nigel Stork made a similar estimation and came to a total of 5 to 10 million arthropod species in the tropics.
EO Wilson 1992 The diversity of life, Penguin Books(see more important references here)
NE Stork (1988) Insect Diversity: Facts, Fiction and Speculation, Biological Journal of the Linnean Society 35: 321-337
T Erwin (1982) Tropical Forests: their richness in Coleoptera and other Arthropod Species, Coleopterists' Bulletin 36: 74-75
Check following WWW pages for interesting information:
World Wide Web Virtual Library: Biodiversity, Ecology, and the Environment A lot of species are listet here but: how many? or do a search under biodiversity and insects (that should give lots of starting points)
Try the links in the MadSci Library for more information on Zoology.