According to a report published by the Zoological Society of London, one-fifth of invertebrates are in danger of extinction. This proportion is similar in vertebrates and plants, but to date no systematic research has been carried out on invertebrates, and many are missing for inclusion in the Red List of threatened species. Scientists of the London association have not investigated all species, but a representative sample of 1,500 species. The data show that some freshwater species are the ones with the highest risk, such as some snails and crabs. The lowest risk is shown by some cantilevers such as butterflies and brooches.