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Eastern Red-rumped Swallow Built a Mud Nest on a Pre-existing Wasp Nest in South Korea

Eastern red-rumped swallow collecting mud for nest building
Research · Behaviour

Citizen scientists in Miryang, South Korea, documented Eastern red-rumped swallows (Cecropis daurica) building a mud nest against a pre-existing, inactive wasp nest beneath a railway bridge. Three to four adults were first seen repeatedly entering and leaving the wasp nest in mid-May 2025.

No nest construction was recorded during June. In early July, the swallows began carrying mud and attaching it to the side of the wasp nest, which served as a physical supporting substrate. By mid-July, the external mud structure was largely complete, but adults were no longer observed entering it. No eggs or nestlings were detected during the observation period.

By early August, the central part of the swallow nest had collapsed. The authors note that the papery, porous and relatively rough surface of the inactive wasp nest may have aided the initial attachment of mud. They also consider the frequent vibrations from passing trains beneath the railway bridge a likely contributor to the structural failure.

The observation provides a documented example of C. daurica using a biological structure built by another animal as a nesting substrate. The authors describe such use as rarely reported for the species and present the record as additional evidence of the range of substrates it can use during nest construction.

Sources and image credit

  1. Lee, H.-J., Kim, J.-R., Lee, Y., Heo, A., & Lee, S.-Y. (2026). Use of a pre-existing wasp nest by the Red-Rumped Swallow (Cecropis daurica): A record based on citizen science. Proceedings of the National Institute of Ecology of the Republic of Korea, 7(2), 63–66. https://doi.org/10.22920/PNIE.2026.7.2.63Primary open-access case report dated 30 May 2026 in South Korea’s national digital knowledge record. The article is distributed under CC BY-NC 4.0. Citizen-science monitoring beneath a railway bridge in Miryang documented three to four adult Cecropis daurica investigating an inactive wasp nest, attaching mud to it in July 2025, largely completing the nest, and later abandoning it without eggs or nestlings before the structure collapsed in early August.

Image: Shatruhanray / Wikimedia Commons — Eastern red-rumped swallow (Cecropis daurica) collecting mud for nest building in Nepal, photographed 12 April 2025; representative behaviour image, not from the South Korean observation · CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ · Source

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