Mystery moth found living inside dead snail shells in England

For nearly a century, one of Britain’s most elusive micromoths seemed to have vanished altogether. Tenaga nigripunctella, a tiny tineid moth described by Haworth in 1828, was last recorded in Great Britain at Dymchurch, Kent, in 1934, and for much of the past century it was thought to be extinct there. Its biology was a complete blank: nobody knew what the larva ate, where it lived, or how it developed. Now, a team working in Dorset has finally cracked the case, reporting the first confirmed observations of the early stages of the genus Tenaga anywhere in the world, and the findings are stranger than anyone expected. The larvae, it turns out, live inside the shells of dead garden snails, feeding on the dried body tissues of their deceased hosts.

The rediscovery began in 2013, when a single adult specimen was found at East Creech Farm, Dorset, by Rachel Terry. Dissection of the genitalia confirmed the moth was indeed T. nigripunctella and not the superficially identical European species T. rhenania. Since then, adults have been seen annually in a small area of Dorset, and between 2014 and 2024 the species has been recorded at one coastal and two inland locations roughly 40 kilometres west of the 2013 site. The new study, published in Nota Lepidopterologica, reviews these modern records alongside historical specimens held in the Natural History Museum, London, documenting the moth’s prior distribution across southern England from Kent to Cornwall and north to Cheshire and Yorkshire, with records also from the Channel Islands, Ireland, and doubtfully Northumberland.

The breakthrough came in July 2023, when observers noticed adults flying close to stone walls, including a dry-stone wall and a mortared wall. On 5 July 2023, an adult was seen flying near a small hole in a mortared wall, with two apparently fresh adults sitting at the entrance to the same hole, suggesting they might have emerged from pupae within it. A large snail shell was visible at the entrance. The hole was no deeper than 15 centimetres. This observation provided the first clue that the larvae might be developing inside dead snail shells, a hypothesis that subsequent searching would confirm in remarkable detail.

Careful examination of dead snail shells lying on ledges, windowsills, and within the wall hole revealed larval frass on seven occasions, in shells identified as the Garden Snail Cornu aspersum and the White-lipped Snail Cepaea hortensis. Each of the two Cornu shells contained a living larva. One was successfully reared to the adult stage, while the other died, but its identity was confirmed from its DNA barcode. When the shells were carefully cut open, the larvae were found close to the centre, with silk and frass distributed within. The blackish gut contents of the larvae and the blackish frass found in the shells almost certainly indicate that the larvae feed on the dried body tissues of the snails, making this the first observation inferring dead molluscan tissue as a food source for a lepidopteran larva in Great Britain.

The final instar larva is translucent whitish or cream-coloured, sometimes tinged yellowish, with dark gut contents often visible through the body wall. The head is translucent pale brown or orangey brown, the prothoracic plate yellowish, and the setae whitish and long, approximately the diameter of the body. Larvae spend most of their time within a delicate silken tube adorned with frass and detritus. Prior to pupation they construct a whitish silken cocoon densely covered with frass and detritus, affixed horizontally to a surface or made within a snail shell. The pupa is over 5 millimetres long, pale brown, and exarate, with antennal appendages extending just beyond the end of the abdomen and dorsal abdominal spines present.

Beyond snail shells, larvae very likely to be Tenaga were also found in silken tubes at the base of stacked plant pots and seed trays containing a scattering of detritus including mouse faeces, dead invertebrates, plant and mineral debris, and spider cobwebs. Traces of likely feeding were observed on dry mouse droppings, where the surface appeared eaten away, and a larva was found within a dead Western Honeybee Apis mellifera. However, no direct observation of feeding has yet been made, and caution is expressed over concluding that all larvae observed were Tenaga, since larvae of the White-shouldered House-moth Endrosis sarcitrella were also found and reared from the same locations. The two species are superficially very similar, especially before the final instar, although unlike E. sarcitrella, the prothoracic plate of T. nigripunctella lacks a median suture. Further work is required to separate these species reliably in the field.

The larvae proved to be quite active, able to move outside their silken tubes many tens of centimetres over several minutes, suggesting they can readily move between food sources in the wild. This mobility fits with observations of frass but no larvae within other snail shells, indicating that larvae may graze one shell and move on to the next. Adult behaviour is equally distinctive. The moth rests characteristically in an inclining posture at about 30 degrees, raised up on extended forelegs and midlegs, and can negotiate spider webs. When disturbed, the exceptionally long antennae, longer than the forewing, wave alternately back and forth almost continually. The flight period extends from early April until the end of August, with a protracted emergence.

DNA barcoding confirmed the species identity of the dead larva. A 658 basepair barcode was obtained using Oxford Nanopore Technologies sequencing and released as GenBank accession PP391031. The sequence is identical to barcodes from specimens from Georgia, Croatia, and the United States, meaning that only a single COI-5P haplotype is known worldwide, and the new sequence is only the fourth known DNA sequence for the species. The barcode is 7.37% pairwise divergent from sequences of T. rhenania from France and Austria. The remarkable genetic uniformity across such widely separated populations suggests the species has been introduced more widely, at least to the USA, and probably also to Australia and South Africa, where it was historically recorded under different names before being synonymised.

The study also reviews the moth’s worldwide distribution, reporting new records for Lebanon and Syria. Historical introductions were temporarily established in Australia, where five examples were collected in New South Wales between 1879 and 1885 and the species is now thought possibly extinct, and in South Africa, where it was described from Cape Town. In Europe, the species is recorded from Madeira, the Azores, the Canaries, northern Spain, France, Germany, the Netherlands, Croatia, Greece, and Poland, with records from Turkey and Israel verified by dissection. Some records from Austria, Switzerland, Bulgaria, and Romania possibly represent misidentifications of T. rhenania, and a partial DNA barcode from Italy on the Barcode of Life Database represents a clear misidentification belonging to that species.

The taxonomic placement of the genus Tenaga, containing only two closely related species, remains debated. Some works retain it in the family Tineidae, subfamily Meessiinae, while Meessiidae has recently been elevated to family status based on molecular phylogenetics. The authors keep Tenaga conservatively in Tineidae, noting that the scavenging lifestyle suggested here is quite out of place for known Meessiidae, whilst it is not unusual for some Tineidae, especially the Tineinae and Hieroxestinae. The larva shows no synapomorphic characters with Meessiidae, such as anal combs for frass flicking, whereas like the Tineinae the pupa has dorsal abdominal spines. The DNA barcode alone is insufficient to place the species with certainty beyond its clear relationship with T. rhenania. The finding of T. nigripunctella and the partial elucidation of its life history in Great Britain is therefore of potential taxonomic as well as key biological interest, and more sequence data from other genes, together with detailed study of the early stages, will be needed to confirm the phylogenetic placement of this enigmatic genus.

Subject of Research: Biology and early stages of the tineid moth Tenaga nigripunctella

Article Title: First early-stage observations for Tenaga Clemens, 1862 with notes on biology and distribution of T. nigripunctella (Haworth, 1828) ( Lepidoptera , Tineidae )

Article References: Sterling, P. H., Stockwell, J., Oughton, J., & Lees, D. C. (2025). First early-stage observations for Tenaga Clemens, 1862 with notes on biology and distribution of T. nigripunctella (Haworth, 1828) (Lepidoptera, Tineidae). Nota Lepidopterologica, 48, 277-288. https://doi.org/10.3897/nl.48.124083

Image Credits: AI Generated

DOI: 10.3897/nl.48.124083

Keywords: Lepidoptera, Tineidae, Tenaga nigripunctella, snail shells, DNA barcoding, Dorset, larval biology, detritivory, Cornu aspersum, Meessiidae, First, early-stage