Gynandromorphy refers to the simultaneous occurrence of male and female morphological traits within one individual. The phenomenon has fascinated entomologists since the nineteenth century, when the first cases in the order Hymenoptera—the bees, wasps, and ants—were described, and it is considered one of the most dramatic of all teratological, or malformation-type, developmental anomalies. In bees alone, more than one hundred cases have now been published, yet the true incidence of gynandromorphism in wild populations is thought to be extremely low, which is why each new specimen attracts attention. A comprehensive review distinguishes three categories of gynandromorphic organization: bilateral, in which male and female traits are divided between the two halves of the body; transversal, in which the division runs across body segments; and mosaic, in which the traits are scattered irregularly.

The underlying causes of these dual-sex bodies are believed to lie in the peculiar genetics of Hymenoptera. Bees and their relatives use haplo-diploid sex determination: males typically develop from unfertilized haploid eggs carrying one set of chromosomes, while females develop from fertilized diploid eggs with two sets. When things go wrong early in embryonic development—through chromosome loss, nondisjunction, or anomalies in fertilization—cell lineages with different ploidy levels can arise side by side. This genetic mosaicism then produces the phenotypic mosaicism visible in the adult. Researchers have also hypothesized that reproductive manipulation by bacterial symbionts of the genus Wolbachia may occasionally generate gynandromorphs, and experimental work has shown that environmental stresses such as temperature shocks during early development can raise the frequency of these anomalies in laboratory systems.

The Andrena florivaga specimen was collected with an insect net on 20 May 2025 in the Schottenbruch nature reserve near Niedermeiser in Hesse, a calcareous semi-dry grassland in the Diemel Valley. Its dual-sex nature became apparent immediately under the stereomicroscope. DNA barcoding of the CO1 gene, performed on internal tissue to preserve the external morphology and sequenced on a portable Oxford Nanopore device, confirmed the species identification with a 100 percent sequence match to a reference sequence of Andrena florivaga. The specimen is thus the first confirmed gynandromorph of its species and one of the most cleanly organized ever described in the genus Andrena.

What makes the mining bee remarkable is the consistency of its bilateral pattern. The left side of the body is predominantly male, the right side predominantly female, and this division runs continuously across the mesosoma, the legs, and the metasoma, affecting both secondary sexual characters and terminal structures. The hair fringe on the left is short and whitish, the typical male condition, while the right side carries short yellowish hairs. Even the punctation of the mesonotum differs: on the left, the punctures are sparse and widely spaced, more than twice a puncture diameter apart, whereas the right side shows the regular, dense punctation of a female, with spacing of only one to two puncture diameters.

The legs tell the story particularly vividly. From the middle legs onward, the left metatarsus is narrow, darkened at its base, and covered with yellowish-white male-type hairs, while the right leg segments are enlarged and broadly orange with orange-yellow pubescence. The right hind leg bears a fully developed orange scopa—the dense pollen-carrying brush of a female bee—along with a well-developed yellow flocculus. The head and forelegs, by contrast, are entirely female on both sides, with no bilateral differentiation at all. This means the bilateral split begins behind the head, a transversal deviation from the otherwise bilateral plan that researchers interpret as the result of temporally offset sex-determination processes acting during embryogenesis.

The terminal region of the specimen is more ambiguous, as is common in these anomalies. A partially developed orange apical fringe and a half-developed pygidium are present only on the right side, and the sting apparatus survives on the right while a deformed male sternite 8 appears on the left. The genital apparatus combines male and female structures without a clearly traceable bilateral boundary, producing a curved, bow-like stinger alongside a gonocoxite that merges diffusely into a setose structure. The authors caution that this limited assignability reflects the limits of purely morphological analysis of complex genital structures rather than a true mosaic organization.

The second specimen, a Nomada lathburiana collected on 6 April 2024 in the Moosheide nature reserve near Hövelhof in North Rhine–Westphalia, presents an entirely different organization. This cuckoo bee, which lays its eggs in the nests of other bees, shows a mainly bilateral separation of male and female traits in the tergites, sternites, mesosomal pubescence, and leg coloration—but within certain body regions the assignments alternate and the transitions blur, making it a predominantly bilateral gynandromorph with mosaic-like elements. The head is mostly female, with red clypeus, labrum, and facial pubescence, yet the area between the eyes and the clypeus and the mandibles are yellow, matching the male. Small nodules, a male trait, appear on the left antenna. On the mesonotum, the left side carries white hairs and yellow tegulae and scutellar spot, while the right side shows red pubescence and reddish-brown structures of the female.

The most striking feature of the cuckoo bee is the decoupling of sex-specific traits within single structures. On the second tergite, the left side shows a narrow female-type yellow spot while the right side carries a large male-type yellow spot; on the third tergite the pattern reverses, with male traits on the left and female traits on the right. The fourth and fifth tergites likewise alternate, and the sting apparatus, though present, bears a bizarre second diverging tip. This intermediate form—neither strictly bilateral nor restricted to the head like the two previously documented gynandromorphs of the same species—demonstrates that gynandromorphic patterns do not follow a uniform appearance even within a single species, and that male and female characters can be distributed independently within the same body region, reflecting complex developmental pathways.

Together, the two specimens expand the known range of gynandromorphic phenotypes in wild bees and underline how much these rare individuals can teach. Because the anomalies affect multiple body segments in clearly defined patterns, they allow precise functional and morphological comparisons of sex-specific traits and provide clues about the temporal dynamics of sex determination. In the genus Andrena, most previously reported cases involved male traits limited to the head, while one Chinese species showed an almost perfectly bilateral split; the new German specimen adds an anterior modification to that bilateral plan. The authors conclude that the considerable variability of gynandromorphic expression, occurring even within a single species, is likely determined by the interaction of several temporally offset developmental processes—rare accidents of embryology that, once in a while, hand scientists a living blueprint of how insect bodies decide what sex to become.

Subject of Research: Gynandromorphy in wild bees: first record in Andrena florivaga and a new case in Nomada lathburiana

Article Title: First record of gynandromorphy in Andrena florivaga and an additional case in Nomada lathburiana from Germany ( Hymenoptera , Apoidea )

Article References: Kettermann, M., Klaren, J., Rupprecht, C., Bleidorn, C., & Fartmann, T. (2026). First record of gynandromorphy in Andrena florivaga and an additional case in Nomada lathburiana from Germany (Hymenoptera, Apoidea). Journal of Hymenoptera Research, 99, 1009-1023. https://doi.org/10.3897/jhr.99.206068

Image Credits: AI Generated

DOI: 10.3897/jhr.99.206068

Keywords: gynandromorphy, wild bees, Andrena florivaga, Nomada lathburiana, Hymenoptera, sex determination, haplo-diploidy, developmental anomaly, bilateral gynandromorph, mosaic traits, Germany, morphology