In the countryside around Rome, a team of Italian entomologists has spent a full field season hunting for one of the least glamorous and least understood corners of the bee world: the cleptoparasitic bees, commonly known as cuckoo bees. Like their avian namesakes, these insects do not build nests or gather pollen for their young. Instead, females sneak into the burrows of other bees and deposit their eggs in the provisioned brood cells, leaving their larvae to devour the pollen stores meant for the host’s offspring. A new faunistic survey, published in the Biodiversity Data Journal, documents 417 individuals belonging to 44 species of these nest invaders from ten genera and three families, collected across four protected areas in the province of Rome between March and September 2025.

The scale of the haul is notable. The recorded community represents roughly 40 percent of all cleptoparasitic bee species ever reported for the Latium region and about 18 percent of those known from Italy as a whole, despite the survey covering only a single year, a single sampling method, and a limited set of rural sites. Five species turned out to be new records for Latium: the cuckoo bee relatives Epeolus julliani, Nomada nausicaa, Nomada carnifex, Nomada cruenta and Nomada connectens. None of them had appeared in regional or national checklists, recent regional studies, or the Global Biodiversity Information Facility, underscoring how fragmented knowledge of wild bee distributions remains even in one of the most intensively studied corners of Europe.

Cleptoparasitic bees make up around 13 percent of the roughly 20,000-plus described bee species worldwide, yet they are chronically under-sampled and poorly assessed. Because their reproduction depends entirely on the presence of suitable hosts, they act as a kind of ecological mirror: where cuckoo bees thrive, wild bee communities are typically diverse and intact. Previous work in Canadian agroecosystems and in urban nature reserves has shown that parasitic bee richness tracks overall bee diversity and declines sharply under environmental disturbance. That sensitivity makes them valuable bioindicators, but it also makes their conservation status hard to judge. The most recent European Red List of Bees flags entire genera as data deficient — Melecta stands at 64 percent, Metadioxys at a full 100 percent — partly because these bees are naturally rare and partly because their taxonomy is a mess.

The study sites themselves tell a story about landscapes. Sampling took place along fifteen fixed 200-by-2-meter transects distributed across four protected areas: the urban Pineto Regional Park and the Laurentino-Acqua Acetosa Reserve, both inside the ring motorway that encircles Rome, and the coastal Litorale Romano State Reserve and the presidential estate of Castelporziano on the Tyrrhenian shore. Transects fell across three agricultural land-use classes, from non-irrigated arable land to pastures and mosaics of farming with natural vegetation. Fieldworkers walked each transect for 50 minutes with entomological nets, only under dry, warm, low-wind conditions, with extra visits in April and May to catch the spring activity peak. Intriguingly, the two sites embedded within Rome’s urban matrix — Pineto and Laurentino — produced high species richness and the highest abundances, suggesting that sizeable agricultural pockets inside a city can still sustain functioning parasite-host communities.

Apidae dominated the catch, contributing 35 of the 44 species and 392 of the 417 specimens. Within it, the genus Nomada — the largest brood-parasite genus on Earth — accounted for 25 species and 215 individuals. The single most abundant species was Eupavlovskia obscura, with 141 specimens netted across nearly every site and month. Halictidae followed with five species and 20 specimens, and Megachilidae with four species and just five individuals. The coastal Litorale Romano site yielded the highest species richness at 26 species, while Castelporziano, despite hosting the most transects, produced the fewest — a reminder that sampling effort was not evenly distributed and that site comparisons should be read with caution.

What sets this survey apart is its integrative taxonomic approach. Rather than relying solely on morphology, the team sequenced a fragment of the mitochondrial cytochrome c oxidase I gene (COI-5P) — the standard animal DNA barcode — from leg tissue, generating 98 new sequences from 43 species and depositing them in the BOLD and GenBank public databases. Among them is the first COI-5P barcode ever recorded for Nomada nausicaa. For specimens whose identity was uncertain under the microscope, the barcode served as an arbitration tool: sequences were compared against reference libraries, and where matches fell below 97 percent similarity or contradicted the morphological call, the researchers built neighbor-joining phylogenetic trees alongside curated Western Palearctic reference sequences to see where their specimens truly sat.

In most cases, molecular clusters lined up neatly with morphological species, confirming identifications with 100 percent sequence similarity in several genera including Coelioxys and Epeolus. But the approach also exposed genuine taxonomic friction. The genus Melecta emerged as the clearest problem child: Melecta leucorhyncha proved polyphyletic, with the study’s specimens splitting into two well-supported clades alongside database sequences, and sequence similarities to references ranging from 96.4 to 99.7 percent. No comprehensive integrative revision of Melecta has ever been attempted; the last major morphological treatment dates to Lieftinck’s 1981 monograph, which itself flagged the difficulty of pinning down stable characters for M. leucorhyncha and the risk of confusing it with the polytypic M. italica. The new trees do separate those two species molecularly, but sparse sampling and an undefined barcode gap — not to mention the well-documented problem of misidentified sequences in public repositories — prevent firm conclusions. The authors conservatively assign their specimens to the melanic Italian subspecies M. leucorhyncha taormina pending a proper revision.

Nomada offered further puzzles. Sequences of N. carnifex clustered with a BOLD specimen labeled as the related N. mutabilis rather than with deposited N. carnifex, and N. connectens shared 100 percent barcode similarity with both N. connectens and N. bluethgeni references. N. sheppardana and N. minuscula, meanwhile, grouped together with N. nigrovaria in a single clade, echoing recent findings that closely related Nomada species can share barcode index numbers, blurring species boundaries. Some of these anomalies likely reflect mislabeled database entries; others may reflect genuinely shared haplotypes among young, closely related species. In every ambiguous case the team fell back on diagnostic morphology when it allowed a confident call. A divergent individual of Melecta albifrons and genetically distinct Eupavlovskia funeraria sequences add further threads for future work to untangle.

Beyond the checklist, the study carries a conservation message. Among the species recorded, Nomada rubiginosa and Nomada blepharipes are already ranked at moderate and critical risk of extinction in Italy, and the Mediterranean Basin — a global hotspot for bee diversity — is simultaneously one of the regions most exposed to warming and aridification. Because cuckoo bees respond quickly to habitat disturbance and depend on healthy host populations, targeted faunistic surveys like this one are a prerequisite for any credible Red List assessment. The authors argue that hand netting alone proved an effective method for these rare insects, outperforming the pan traps and Malaise traps often favored in standardized monitoring, and that targeted surveys consistently outperform general community censuses at detecting them.

The broader takeaway is twofold. First, even a modest, single-season, single-method survey in familiar European countryside can still add regional firsts and thousands of kilometers of distributional detail for poorly known insects — evidence that basic faunistics remain far from exhausted. Second, DNA barcoding is not just a rubber stamp for morphology; deployed critically, it is a discovery engine that flags cryptic lineages, exposes database errors, and tells taxonomists exactly where to dig next. With 98 new COI-5P sequences now in the public domain, including the first for Nomada nausicaa, the cuckoo bees of central Italy have moved a little further out of the shadows — even as the genus Melecta reminds everyone how much systematic work still lies ahead.

Subject of Research: Cleptoparasitic bee diversity and DNA barcoding in rural protected areas of Latium, central Italy

Article Title: Cleptoparasitic bees ( Apoidea , Anthophila ) in rural protected areas in Latium (Italy): a faunistic survey through an integrative taxonomic approach

Article References: Annessi, M., Riccieri, A., Polidori, C., Mei, M., & Di Giulio, A. (2026). Cleptoparasitic bees (Apoidea, Anthophila) in rural protected areas in Latium (Italy): a faunistic survey through an integrative taxonomic approach. Biodiversity Data Journal, 14, Article e193040. https://doi.org/10.3897/bdj.14.e193040

Image Credits: AI Generated

DOI: 10.3897/BDJ.14.e193040

Keywords: cleptoparasitic bees, cuckoo bees, DNA barcoding, COI-5P, integrative taxonomy, Nomada, Melecta, Latium, Italy, faunistic survey, bee conservation, BOLD