How many species of arthropods visit flowers?

Abstract

The majority of living plant species are pollinated by insects, and this interaction is thought to have played a major role in driving the diversification of modern angiosperms. But while flower–insect interactions have been well studied from the perspective of plants in the form of pollination biology, few studies have been carried out from an entomological perspective, where flowers are resources to exploit. As a consequence, it remains unknown how many insect species actually utilise floral resources, especially since many flower-visitors do not carry out pollination and may therefore be widely ignored in pollination studies. In this review, I attempt to present an overview of the taxonomic range of flower-visiting invertebrates and estimate the proportion of described species that regularly utilise flowers. The flower-visiting habit has likely evolved independently hundreds of times across more than a dozen modern invertebrate orders. I speculate, based on reviewing the literature and discussions with experts, that ~30 % of arthropod species (>350,000 described species) may regularly utilise flowers to feed, find a mate, or acquire other resources. When extrapolated to the estimated global diversity of the phylum Arthropoda, perhaps more than a million species regularly visit flowers. However, generating more accurate estimates will require much more work from the perspective of flower-visiting insects, including the often-ignored species that do not pollinate host plants. In particular, sampling techniques in addition to traditional observation protocols should be encouraged to ensure that all flower-visitors are recorded. Greater efforts to identify flower-visiting species beyond the level of order or family will also enhance our understanding of flower-visitor diversity.