Geographically Bulgaria is a natural bridge between Europe and Asia. The varied relief and the climate maintain the wildlife. The 35,000 recorded species are believed to be half of what the country actually has. Insects are most numerous (30,000 species); the arachnida place second. 1200 of the animal species in Bulgaria are endemic and occur in a definite area; of them 790 are Bulgarian endemics and 410 are Balkan endemics. The vertebrata are completely studied with 730 species of which 399 bird species and 93 mammal species. This makes Bulgaria one of the countries with the greatest biodiversity in Europe.