Species richness is one of the fundamental metrics of biodiversity. Estimating species richness helps spotlight taxonomic groups that are particularly under-studied, such as the highly diverse Darwin wasps. The only available estimate of the number of Darwin wasps in the Afrotropics proposed almost 11,000 species, compared to the 2,322 recorded species. However, it relied exclusively on the ratio of morphospecies to described species in Henry Townes' personal collection. We provide an updated estimate of the Afrotropical Darwin wasp species, using empirical data from multiple sources, including the increase in species numbers following generic revisions, morphospecies sorting in natural history collections, and diversity patterns of better-studied insects (butterflies) for extrapolation. Our analyses suggest that our knowledge of Darwin wasps is highly incomplete, with only 13-22% of species known in the five most extensively studied countries in the Afrotropics. We estimate 9,206-15,577 species of Darwin wasps within the entire Afrotropics, with the highest concentration expected in the Equatorial Afrotropics and Madagascar. Due to data constraints, our approach tends to underestimate diversity at each step, rendering the upper estimate (15,577 species) more realistic. We highlight reasons contributing to the gap between recorded and estimated species richness, including logistical and financial factors, as well as post-colonial influences.

Agricultural Research Council Plant Health and Protection Biosystematics Pretoria South Africa

Biology Centre of the Czech Academy of Sciences Institute of Entomology Ceske Budejovice Czech Republic

Canadian National Collection of Insects Arachnids and Nematodes Agriculture and Agri Food Canada Ottawa Ontario Canada

Department of Biological Sciences University of Cape Town Cape Town South Africa

Department of Biology University of Central Florida Orlando Florida United States of America

Department of Life Sciences University of Siena Siena Italy

Faculty of Science University of South Bohemia Ceske Budejovice Czech Republic

Naturhistorisches Museum Basel Basel Switzerland

Naturhistorisches Museum Wien Wien Austria

Research and Exhibitions Department South African Museum Iziko Museums of South Africa Cape Town South Africa

The Natural History Museum Cromwell Road London United Kingdom

University of Bern Institute of Ecology and Evolution Bern Switzerland

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