Village Gat Koto (35°03'38"N, 71°36'59"E; Altitude = 2333.12 m) (Fig. 1), Shahikot, Tehsil Barawal Bandi, District Dir Upper, Malakand Division, Khyber Pakhtunkhaw Province, Pakistan. Over freshly fallen snow (Fig. 2A, B), collected on 27^th December 2021.

Male from type locality, anterior, posterior and mid body segments (1 cm each) as SEM sample, rest of the body preserved in 96% ethanol. Deposited in the Pakistan Museum of Natural History (accession number: PMNH-ZSD-INV-NEMA-0001).

Female from type locality, anterior, posterior and mid body segments (1 cm each) as SEM sample, rest of the body preserved in 96% ethanol. Locality of the allotype is the same as that of the holotype (35°03'38"N, 71°36'59"E; Altitude = 2333.12 m). Deposited in the Pakistan Museum of Natural History (accession number: PMNH-ZSD-INV-NEMA-0006).

Anterior, posterior and mid body segments (1 cm each) of two males and one female as SEM sample and rest of the specimens preserved in 96% ethanol. One further male specimen with the anterior end mounted on a slide and the rest preserved in 96% ethanol. All these paratypes belong to the same locality as type locality (35°03'38"N, 71°36'59"E; Altitude = 2333.12 m). Accession numbers for the paratypes are: PMNH-ZSD-INV-NEMA-0002 to PMNH-ZSD-INV-NEMA-0005.

Fragments of 11 further specimens preserved in 96% ethanol (n = 6 from Gat Koto, 35°03'38"N, 71°36'59"E, the type locality and n = 5 from Shaltaloo, 35°03'26"N, 71°37'33"E) (Fig. 1, type locality and location 1) and 4 specimens from Karang (35°28'43.8"N, 72°57'39.8E District Upper Kohistan; Fig. 1, location 2) as gold coated SEM stubs are in possession of QJ in the Institute of Zoological Sciences, University of Peshawar, Peshawar, Pakistan.

Further confirmed spotting on snow and from water are reported to the authors from the following locations: village Hattan Dara, District Dir Upper Khyber Pakhtunkhwa, Pakistan (35°12'30"N, 71°52'29"E), altitude: 1447.68 m (Fig. 1, location 3); Dir Bazar, District Dir, Upper Khyber Pakhtunkhwa, Pakistan (35°11'30.0"N, 71°52'29.0"E) (Fig. 1, location 4); village Jijal, Tehsil Pattan, District Lower Kohistan Khyber Pakhtunkhwa, Pakistan (35°12'29"N, 71°52'29"E), altitude: Altitude = 1551.11 m (Fig. 1, location 5); village Chatal Kayal Khar, District Lower Kohistan, Khyber Pakhtunkhwa, Pakistan (35°10'08"N, 73°01'34"E), altitude: 1418. 87 m (Fig. 1, location 6); Kakul Road, District Abbotabad, Khyber Pakhtunkhwa, Pakistan (34°10'22"N, 73°14'09"E), altitude: 1223.15 m (Fig. 1, location 7); Mian Kaley Munda, District Lower Dir, Khyber Pakhtunkhwa, Pakistan (34°49'19"N, 71°40'21"E) , Altitude = 779.8 m (from rice paddy) (Fig. 1, location 8); Fatehpur, Tehsil Khwazakhela Distrct Swat, Khyber Pakhtunkhwa Pakistan (35°04'10"N, 72°29'11"E), Altitude = 1418. 87 m (from water) (Fig. 1, location 9). These specimens were not investigated morphologically.

The word “nix” is Latin for snow. The species epithet “nixus”, therefore, is chosen as the worms were collected over freshly fallen snow.

Male (n = 11); Length/width (n = 04):185 mm/1 mm, 165 mm/1 mm, 110 mm/0.9 mm, 183 mm/0.9 mm; color: yellowish brown to light brown when alive, turned dark brown after preservation in 70% ethanol. Live specimens carried light creamy white spots on the cuticle, which were in greater density on anterior to mid-body and became scant towards posterior; spots almost lacking in the posterior region. Two creamy lines, prominent in the anterior, extended along the midline of the body dorsally. Anterior tip with white calotte followed by a dark black collar (Fig. 2D). Posterior end with semi-circular postcloacal crescent, and two blunt lobes (Fig. 2F; length and width measured in two specimens = 0.6 mm/0.32 mm, 0.7 mm/ 0.3 mm). The lobes had depressions on inner ventro-medial side towards proximal end in scanning electron micrographs (Fig. 3E, F). Cuticle surface smooth throughout, sometimes with roundish to polygonal imprints (Fig. 3B). Spines are present in the anterior end (Fig. 3A, C). They showed greater density at the anterior half of the body and decreased towards posterior. Spines in the cloacal region and over the tail lobes were sparsely distributed and short (Fig. 3D–F). The cloacal opening could not be observed very well, as it was either covered by dirt (Fig. 3E) or appeared to be absent (Fig. 3F). The postcloacal crescent is semicircular and directly at the level where the tail lobes divide (Fig. 3D–F).

Figure 3.

Scanning electron micrographs from male specimens. A. Dense bristles on the anterior end of new male 1; B. Magnification of bristles and cuticular surface; C. Bristles on the anterior end of the holotype; D–F. Lateral or ventral views on the posterior ends of several specimens, showing the cloacal opening (co) and the postcloacal crescent (pcc).

Female (n = 13); Length/width (n = 05): (160 mm/1 mm, 175 mm/1.1 mm and 255 mm/1 mm, 210 mm/1 mm, 187 mm/1.1 mm); Color: yellowish brown to brown in life (Fig. 2E) and turned dark brown in 70% ethanol. Like males, living females also carried light creamy white spots on the cuticles that were dense on anterior till mid body but became scarce towards posterior. These spots are almost always lacking in the posterior end. Two creamy lines, prominent in anterior region, were running along the dorsal midline of the body. The anterior tip had a white calotte followed by a dark black collar. The anterior region had a dense covering of fine bristles visible in glycerin mounted 10% KOH cleared specimen (Fig. 2C) and scanning electron micrograpy (Fig. 4B–E). Spines become much less abundant and shorter in the middle and posterior body region. The cuticular surface is smooth, as in males (Fig. 4A). Posterior end round, bearing a vase-like cloacal opening at the tip (Fig. 4B). Some females had a sperm drop on their posterior end (Fig. 2E).

Figure 4.

Scanning electron micrographs from female specimens. A. Smooth cuticle in female specimen from Kohstan; B, C. Dense bristles in the anterior end of allotype (B) and female specimen from Kohstan (C); D. Magnification of bristle; E. Lateral view on bristles; F. Posterior end with cloacal opening (co) in the female paratype; G. Bristles in the anterior end.

The smooth cuticle as well as the morphology of the male and female posterior end correspond to several other species in the genus Gordius and do not set the specimens from Pakistan apart from other species. What is unique is the dense presence of spines in the anterior end. Several Gordius species have sparsely distributed short spines on the body cuticle (see character 4 in table 1 in Schmidt-Rhaesa 2010), but to our knowledge only in two species bristles were described in the anterior end. In Gordius terrestris from North America, there are very fine bristles (see e.g. image 1B in Anaya et al. 2019), in some specimens these seem to be lacking (e.g. image 3B in Analya et al. 2019). Gordius terrestris has polygonal areoles on the cuticle, in contrast to the Parkistan specimens. The other species with bristles in the anterior region is Gordius wulingensis from China (Zou et al. 2025), but in smaller number than in the specimens from Parkistan. As most diagnostic characters for identifying species in the genus Gordius are so far found in the male posterior end, less attention might have been put to the anterior end. Nevertheless, the presence of dense bristles in the anterior end is a unique character and justifies the description as new species.

Mid-body segments of adult male fixed in 70% ethanol and mounted in Puri’s medium for insect clearing and mounting took a year to become clear enough for microscopy. Female specimens preserved in 70% ethanol for a week when placed in 10% KOH, also an insect and arachnid clearing agent, overnight was completely dissolved leaving behind a shroud cuticle all along body except the anterior collar (calotte was also dissolved) and posterior tip (Fig. 3A inset, B). The collar and posterior cloaca containing tips, however, became nicely cleared for microscopy. This treatment also helped revealing bristles on the cuticle around collar (Fig. 3B). Adult mated females (Fig. 2E with sperm on the posterior end) lived for more than 2 months in spring water when reared in lab from 21^st December, 2020 to 5^th March 2021 (n = 2) and 29^th December, 2021 to 13^th March, 2022 (n = 3) at room temperature with average day and night temperature of 20 °C and 5 °C December through February.

The finding of nematomorphs on snow is quite remarkable. As this was observed repeatedly, we believe that this is a natural occurrence. However, the life cycle of Gordius nixus remains completely unknown. No host species was found close to where worms were found. The life cycle of horsehair worms is still not well understood, but at least in temperate regions the life cycle seems to be coupled to seasons. For example in central Europe, free living specimens are found most abundantly in summer and fall and at least in some species there appear to be species-specific time windows of occurrence (e.g. Schmidt-Rhaesa et al. 2005). Adult specimens die after deposition of gametes and nematomorphs might survive the winter either as eggs, larvae or within the intermediate host (e.g. Bolek et al. 2013). There are some occasional records of finding adult nematomorphs during winter and under icy conditions (e.g. in Mühldorf 1913), but such records are rare and seem to be the exception.

The association of G. nixus with snow is a new and exceptional phenomenon among nematomophs and deserves further observations concerning seasonality, partner finding and hosts.

Gordius nixus sp. nov. is the first formal description of a horsehair worm from Pakistan. As we are aware of further, unpublished observations of horsehair worms, we are sure that their diversity and distribution is much higher in Parkistan than currently known.

Like Parkistan, little is known about the Nematomorpha from neighboring countries. There is no record from Afghanistan and only three records (Chordodes anthophorus, C. bipilus, Parachordodes sp.) from Iran, all from the northern region (Kirjanova 1957; Mohtasebi et al. 2021, 2022). From India, a total of 22 species (and some further unidentified records) are known, but the majority of them are from Eastern India (Yadav et al. 2021) and only three records come from northwestern regions, namely Punjab (Paragordius stylosus, see Camerano 1912) and Uttarakhand (Acutogordius doriae and Parachordodes roccatii, see Camerano 1908, 1912). From China, 17 species from 5 genera are reported, including 6 Gordius-species (Schmidt-Rhaesa 2013). With the exception of Gordius wulingensis (Zou et al. 2025), the Gordius species are not sufficiently well described to allow an in-depth comparison.

Although part of the region is dry, there are other parts, which have streams and rivers and appear well suited for nematomorphs. Therefore, the biodiversity of horsehair worms in Pakistan as well as in the neighboring regions is expected to be considerably higher than the current records suggest. Hopefully, records such as this one help to motivate the search for horsehair worms and report them.