A new study on mayflies of the genus Ecdyonurus illustrates just how multifaceted and surprising reproductive behavior in nature can be. Entomologists at the State Museum of Natural History Stuttgart (SMNS), using state-of-the-art computed tomography, have analyzed the mating rituals of these insects in detail for the first time. The results reveal surprising mechanisms of specially adapted reproductive organs that enable the mayflies' acrobatic mating flight. The study not only provides fascinating insights into the extraordinary sexual behavior of these short-lived creatures but also contributes significantly to our understanding of the evolution of complex reproductive mechanisms in flying insects. The findings were published in the journal Insect Systematics and Diversity.
“Swarm Kamasutra”: An Acrobatic Aerial Mating Ritual
The life of adult mayflies, whose larvae develop in freshwater, is brief. After emergence, the insects have very little time, which they use for an impressive mating dance that usually takes place in swarms over bodies of water. Copulation itself is an acrobatic act in the air: the male approaches the female from below, grasping her at the thorax with elongated forelegs and at the rear with specialized genital forceps (claspers), curving his abdomen upward to initiate mating.
“The acrobatic mating flight, combined with direct internal fertilization and a unique posture, is a highly specialized behavior and evolutionarily remarkable,” explains Benedict Stocker, lead author of the study and entomologist at the SMNS. “Our research provides valuable insights into the extraordinary lifestyles and anatomical peculiarities of these animals and contributes to a better understanding of insect evolution.”
Micro-CT images: New Insights Thanks to Modern Imaging
To understand exactly what happens inside the female during mating, entomologists of the SMNS collaborated with computed tomography experts from the Karlsruhe Institute of Technology (KIT). To study the animals, mating pairs were caught mid-air with a net and immediately fixed in their mating position using freezing spray. Using micro-CT scans, the scientists then succeeded in creating the first three-dimensional representation of the interplay of the genitalia during mating and clarifying the underlying mechanisms.
A Reproductive Organ with a Sophisticated Mechanism
The investigations revealed remarkable facts: male mayflies are equipped with a 0.8 mm long, paired penis, consisting of a common shaft and two separate penis lobes, each with its own genital opening. Correspondingly, the females possess two oviducts that open separately into a copulatory pouch located on the underside of the abdomen. Particularly conspicuous in the male genitalia are two penial spines, which play a special role during mating.
“During mating, powerful muscles cause a deformation of the penis so that the penis lobes fold over, the spines extend, and they prick into the female's copulatory pouch. This stretches the pouch, allowing it to receive the sperm. At the same time, these ‘sex spines’ ensure that the organ is securely anchored during copulation,” says Dr. Arnold Staniczek, mayfly expert and curator of aquatic insects at the SMNS.
Significance for Insect Evolutionary Research
The acrobatic mating flight, combined with internal fertilization and a specialized posture, represents an extraordinary behavioral trait and an evolutionary innovation of mayflies. The study shows that, unlike in other insects, the male reproductive organ in mayflies is paired and undergoes a change in shape during mating to serve as an anchor within the female. Overall, these findings offer valuable insights into the reproductive biology of mayflies and expand our understanding of the evolution of mating behavior in insects.
For editorial offices
Original publication:
Stocker, F.C.B., Gamba, R., Van de Kamp, T., Hamann, E., Zuber, M., Vagovič, P., Staniczek, A.H. (2026): When mayflies have an erection: Functional morphology of the genitalia in Ecdyonurus (Insecta: Ephemeroptera: Heptageniidae). Insect Systematics and Diversity 10(2): ixag011.
DOI: https://www.doi.org/10.1093/isd/ixag011
Publication Date: 12.03.2026
Science Blog:
You can find an article by the authors on the Science Blog of the State Museum of Natural History Stuttgart at:
https://www.naturkundemuseum-bw.de/en/research/science-blog/better-safe-than-sorry-the-bizarre-sex-life-of-mayflies
Contact:
Dr Arnold Staniczek
State Museum of Natural History Stuttgart, Germany
Department of Entomology, Curator for Aquatic Insects
T: ++49/(0)711/8936/239
E: arnold.staniczek(at)smns-bw.de
M.Sc. Benedict Stocker
State Museum of Natural History Stuttgart, Germany
Department of Entomology
T: ++49/(0)711/8936/2817
E: benedict.stocker(at)smns-bw.de
Dr. Arnold Staniczek and Benedict Stocker are happy to answer your questions and are available for interviews.
Media contact:
Meike Rech
State Museum of Natural History Stuttgart, Germany
Communications/Press Department
T: ++49/(0)711/8936/107
E: meike.rech(at)smns-bw.de
Image material:
Image 1: 1_ Mayfly Ecdyonurus venosus_SMNS_Staniczek
Image description: Male of the mayfly species Ecdyonurus venosus.
Copyright: SMNS/A. Staniczek
Image 2: 2_ Mating of the mayfly Ecdyonurus venosus_SMNS_Staniczek
Image description: Ecdyonurus venosus mating. The female is on top, the male below. Their body length is approximately 1.2 cm.
Copyright: SMNS/ A. Staniczek
Image 3: 3_Penis_Ecdyonurus_dorsal_SMNS_Stocker_Gamba
Image description: Penis of Ecdyonurus venosus, ventral view. Left: at rest; Right: during mating. Reconstruction from µ-CT data.
Copyright: SMNS, B. Stocker/R. Gamba
Image 4: 4_Penis_ Ecdyonurus venosus_lateral_SMNS-Stocker_Gamba
Image description: Penis of Ecdyonurus venosus, dorsal view. Left: at rest; Right: during mating with extended penial spines. Reconstruction from µCT data, length of penis approx. 0.8 millimetres.
Copyright: SMNS, B. Stocker/R. Gamba
Image 5: 5_Female Ecdyonurus venosus_SMNS_Staniczek
Image description: Female of the mayfly species Ecdyonurus venosus.
Copyright: SMNS/A. Staniczek
The use of this image material is permitted only with the appropriate copyright notice and exclusively in the context of reporting on this press release. Thank you.
State Museum of Natural History Stuttgart:
The State Museum of Natural History Stuttgart is a future-oriented research and communication institution. Its research collections, the archives of diversity, comprise over 12 million objects. The museum researches the evolution of life, analyses the biodiversity of various ecosystems and communicates research findings to the public.