Co-evolution Numbers of species
 Many species are parasites or are specialised to live in one or a few hosts. A single species of tropical tree is, on average, a host to 162 host-specific beetle species. The data comes from fieldwork where virtually all the insects in a tree's canopy are collected and analysed. The number is 30 million. Erwin T.L. 1982. This contrasts rather strongly with the total of 1.4 to 1.8 million species which have already been described.