Pollen Specialist Cuckoo Bees of the United States

Jarrod Fowler (2026)

Holcopasites heliopsis

Nomada obliterata

Stelis louisae

Triepeolus concavus

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Introduction

This website compiles associations among native cuckoo bees, native pollen specialist bees, and native host plants from the United States. First, pollen specialist cuckoo bees are defined and methods are described. Next, a table composed of cuckoo bees with associated host bees and host plants is presented. Last, advice about conserving native pollen specialist cuckoo bees is provided. Please note that this compilation is very incomplete and in progress. Many hosts of kleptoparasitic bees are unknown, incompletely known, or incorrect. Researchers are invited to add information to this website. Email records to: j@jarrodfowler.com

Visit:
Fowler, J. (2020). Pollen Specialist Bees of the Western U.S.
Fowler, J. (2020). Pollen Specialist Bees of the Central U.S.
Fowler, J. & Droege, S. (2020). Pollen Specialist Bees of the Eastern U.S.

Pollen Specialist Cuckoo Bees

Roughly 20% of ~3,600 species of bees native to the United States are cuckoo bees*. Cuckoo bees are kleptoparasites who neither construct nests nor collect pollen. Cuckoo bees lay eggs in the nest cells of other pollen-collecting bee species. Cuckoo bee larvae hatch, kill host eggs, larvae, or other brood parasites using modified mandibles, and steal cell provisions.

Regionally, 25% to 60% of U.S. native bees are pollen specialists who only collect pollen from one plant family, a few related plant genera, or only one plant genus or species. Pollen specialist cuckoo bees are herein defined as species of cuckoo bees who only kleptoparasitize pollen specialist bees and whose larvae only eat pollen from particular plants.

Cuckoo bees are the apex of bee communities: diverse populations of cuckoos indicate ecological health. However, cuckoo bees often are rare, have small populations, rely on specific hosts, and can be more prone to extinctions than other bees. Therefore, restoration of native plants that feed pollen specialist bees who host cuckoo bees should be prioritized.

*There are more species of cuckoo than social bees, such as Bumble Bees.

Methods

Records of native cuckoo bees observed in or near nests of host bees were compiled from online sources, peer reviewed articles, technical bulletins, and personal communications. If cuckoo bees were indigenous to the United States without human intervention, then cuckoo bees were defined "native". This study only includes bees that are native and documented as present in at least one county of at least one of the 48 contiguous states.

Definitions of bee conservation status were averaged across ranges. If there were on average: between one and 100 records, then bees were defined "Rare"; between one and 500 records, then bees were defined "Uncommon-Rare"; around 500 records, then bees were defined "Uncommon"; between 500 and 1000 records, then bees were defined "Common-Uncommon"; around 1000 or more records, then bees were defined "Common".

Results

Pollen specialist cuckoo bee species of the United States are alphabetically tabulated with associated host bees and pollen plant families in Table 1. Three families, four subfamilies, 17 tribes, 24 genera, nine subgenera, and 76 species of pollen specialist bees were listed. The bee family with the most pollen specialists was Apidae (73 spp.), while the most speciose subfamily was Nomadinae (67 spp.), tribe was Epeolini (31 spp.), genus was Nomada (17 spp.), and subgenus was Oreopasites (four spp.). The most recurrent authorities (N = 24 authors) were Ezra Townsend Cresson (1838–1926, 20 spp.), Theodore Dru Allison Cockerell (1866–1948, 12 spp.), and Charles Robertson (1858–1935, eight spp.). Most species were first described during years 1878 (nine spp.), 1962 (seven spp.), and 1863 (five spp.).

The states most inhabited by pollen specialist cuckoo bees were: Arizona (38 spp.), California (38 spp.), and Minnesota (34 spp.). Of the 76 species of pollen specialist cuckoos, three spp. were recorded only in California and two species were recorded only in Arizona and zero species were recorded across all 48 states. Overall, 44 bee species were considered "Rare", while 22 spp. were “Uncommon-Rare", 5 spp. were "Uncommon", 4 spp. were “Common-Uncommon", and only one species was "Common" (Nomada pygmaea Cresson, 1863). The months of activity for specialist cuckoo bees were July (52 spp.), June (47 spp.), August (47 spp.), May (43 spp.), September (34 spp.), April (25 spp.), October (12 spp.), March (11 spp.), February (1 spp.), November (0 spp.), December (0 spp.), and January (0 spp.). Oftentimes, pollen specialist cuckoo bees had three month (18 spp.), four month (18 spp.), or five month (14 spp.) flight periods.

Ninety-one species of host pollen specialist bees were listed. The most recurrent host bee family (N = six) was Andrenidae (43 spp.), genus was Colletes (25 spp.), and species were Dieunomia (Dieunomia) heteropoda (Halictidae: Nomiinae) (three spp.) and Svastra (Epimelissodes) obliqua (Apidae: Apinae: Eucerini) (three spp.). Pollen specialist cuckoos often parasitized one (53 spp.) or two (14 spp.) species of host bee. The most recurrent host plant family was Asteraceae (25 cuckoo bee spp.). The most recurrent host plant genera (N = 92) associated with pollen specialist bee species were all members of Asteraceae: Helianthus L. (20 spp.), Solidago L. (16 spp.), Rudbeckia L. (14 spp.), Symphyotrichum Nees (13 spp.), Grindelia Willd. (11 spp.), and Verbesina L. (10 spp.).

Tables

Table 1. Pollen specialist cuckoo bee families (N = three), genera (N = 24), and species (N = 76) with taxonomic authorities, distributions according to records from 48 states, national conservation status (Common, Uncommon, or Rare), phenology, host bee species (N = 89), and host plant families or genera. Cuckoo bee families with member genera, subgenera, and species are presented in ascending alphabetical order; families, subfamilies, and tribes link to BugGuide profiles; species link to Discover Life species profiles. Arthropoda: Hexapoda: Insecta: Hymenoptera: Aculeata: Anthophila (Apoidea):

Recommendations

Pollen specialist cuckoo bees of the United States were most often associated with the most frequent pollen specialist bee family (Andrenidae) and keystone plant family (Asteraceae) of the U.S.. Pollen plants were regularly community dominant species or had ephemeral early/late season blooms and easily accessible floral morphologies. Pollen specialist cuckoos had 30 singular associations with single host bees and eight unique relationships with single host plants: Calochortus, Erythronium, Hydrophyllum, Lysimachia, Packera, and Verbena.

Nearly 87% of the pollen specialist cuckoo bees listed were rare (58% = "Rare" + 29% = "Uncommon-Rare"). Pollinator habitat restoration projects should prioritize practices that foster diverse communities of host plants for pollen specialist cuckoos. Practices including beetle banks, companion plants, cover crops, field borders, hedgerows, insectaries, meadows, pastures, and riparian buffers should be composed primarily of host plants for specialist bees. Regional native plant horticulturists and nurseries should prioritize the propagation of ecoregional pollen plants for specialist bees.

Restoration practices can protect native pollen specialist cuckoo bees from population declines and extinctions, while identically supporting other managed and wild beneficial insects, providing wildlife habitat, reducing weeds and erosion, improving soil health and water quality, regulating pests, offering harvestable products, and bettering aesthetics. Therefore, habitat restoration for native pollen specialist cuckoo bees works synergistically to promote strong sustainability across the United States.

Acknowledgements

Hannah Cave Stout, Heather Holm, and Sam Droege for comments. John Ascher for state attributions. Authors for descriptions. BugGuide and Discover Life groups for information.

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Updated: II-2026