Mermis nigrescens

Mermis nigrescens	Contents	Rev 09/14/2026
	Classification	Hosts
	Morphology and Anatomy	Life Cycle
Return to Mermis Menu	Economic Importance	Damage
	Distribution	Management
Return to Mermithidae Menu	Feeding	References
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Classification:

Enoplea

Dorylaimia
Mermithida

Mermithina: Mermithoidea; Mermithidae; Mermis nigrescens Dujardin, 1842

Type species of the genus

Synonyms:

Mermis subnigrescens Cobb, 1926

Mermis meisseneri Cobb, 1926

Mermis kirgisica Kiryanova, Karavaeva & Romanenko, 1959

Morphology and Anatomy:

General characteristics:

Cuticle with criss-cross fibers
Mature females actively climbing to the upper parts of plants in warm moist conditions
Head rounded. Mouth apical, surrounded by slight swelling approximately 15mm in diameter and 5mm deep.
Paired lateral lip papillae (15mm high); four cephalic papillae;
Paired very small amphids posterior to level of cephalic papillae.
Tail conoid, slightly flattened ventrally, convex dorsally.
Vestigial excretory pore present.

Female:

Post-parasitic females twice the length of post-parasitic males
Generally white color with eggs in uterus showing as a core of golden brown, except at the region of the vagina.
S-shaped vagina without vulval flap
Vulva a longitudinal slit at mid-body
Mature females with a yellowish pigment (ocellar heomoglobin)near the apical end above the nerve ring (ocelli)
Thick, smooth brown eggs with polar knobs and branched filaments at the poles (byssi)

Male:

Spicules paired, separate, strongly curved; tips curving towards each other; head of spicule not wider than shaft
55-75 genital papillae arranged in three distinct single rows, except for medial row in which 3-6 papillae are alternately offset immediately anterior, and occasionally posterior, to genital opening; medial row usually longer than lateral row
Til conoid and slightly flattened ventrally.

Ref: Presswell et al., 2015

Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:

Mermis nigrescens has a wide distribution, occurring in Europe, Asia, and North and South America. It has become established in Tasmania since the introduction of European earwigs (Baker & Capinera, 1997). The species has been reported from New Zealand based on obserovations that M. subnigrescens is common in earwigs in Canterbury; M. subnigrescens has since been synonymized with M. nigrescens by Nickle (1972).

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Feeding:

As with other Mermithidae, there is a stichosome consisting of a longitudinal serial duplication of esophageal glands (stichocytes) which are exterior to the esophagus musculature, each with a duct into the esophageal lumen
In the later stages of development, stichosome separates from the intestine, which becomes a trophosome in which the walls and lumen of the intestine disappear resulting in a syncyteal structure. with no anal opening to the exterior.

European earwig host and newly-emerged juvenile of Mermis nigrescens
Scale bar 1 cm
Photograph from Presswell et al. 2015

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Biology and Ecology:

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Life Cycle:

The life cycle of Mermis species is unusual in that they infect the insect host via passive infection - the ingestion of embryonated eggs which are deposited on foliage - as opposed to that of most other Mermithidae, which hatch from the eggs in water and actively penetrate the host (Christie, 1937; Baylis, 1944, 1947; Poinar, 1983). Adult females of some Mermis species deposit eggs on vegetation from which they are ingested by herbivorous insects; others deposit eggs in soil from where hatched larvae migrate to the surface and penetrate available hosts. After ingestion, juvenile nematodes (about 750 um long), penetrate the gut wall and enter the body cavity of the host insect (Presswell et al., 2015)

Infection by Mermis nigrescens,inhibits development of the ovaries in grasshoppers, and the host may die before or after the nematodes emerge from its body.

After emerging from the host, the nematodes enter the soil where they grow to the post-parasitic adult stage in 2-4 months and become sexually mature. They may remain in the soil for up to 3 years although a two-year life cycle is usual. Adults of M. nigrescens may either mate, or the females reproduce the parthenogenetically.

Adult males of M. nigrescens are about 40-60 mm long; females 60-160 mm. Males are not as long-lived as are the females. Females with fully developed eggs migrate to the soil surface and deposit eggs on vegetation only after rainfall, often in the morning hours before the sun dries the foliage. Up to 14,000 eggs may be produced per female. When laden with eggs, the tan-colored females appear to have a dark stripe running the length of the body, but this dark coloration disappears as the eggs are deposited. The brown or reddish-brown eggs are about 50 um in diameter. They have a cluster of branched filaments at each pole. As the leaf or soil surface dries, the filaments adhere to the substrate and the eggs are anchored.

Since egg deposition occurs in moist conditions, parasitism of grasshoppers and other hosts can be enhanced irrigation.


Mermis nigrescens on foliage	Mermis nigrescens eggs on leaf	Mermis nigrescens juvenile emerging from grasshopper
Photographs from Shelton: Biological Conrol; Cornell University College of Agriculture and Life Sciences

For Ecophysiological Parameters for this species, click	If species level data are not available, click for genus level parameters

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Ecosystem Functions and Services:

Parasitic larvae of Mermis nigrescens have been reported from a large number of insect hosts, mainly of the order Orthoptera (Baylis, 1944; Baker & Capinera, 1997), and from bumblebees (Bombus) in the USA (Tripodi and Strangs, 2018). The species also occurs in the European earwig in Tasmania (Crowcroft, 1947), Canada (Wilson, 1971) and Britain (Baylis, 1944).

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Management:

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References:

Baker, G.L. &and Capinera, J.L. 1997. Nematodes and nematomorphs as control agents of grasshoppers and locusts. Memoires of the Entomological Society of Canada 171:157-211.

Baylis, H.A. 1944. Observations on the nematode Mermis nigrescens and related species. Parasitology 36:122-132.

Capinera, J.L. 1987. Observations on natural and experimental parasitism of insects by Mermis nigrescens Dujardin (Nematoda: Mermithidae). Journal of the Kansas Entomological Society 60: 159-162.

Cobb, N.A. 1926. The species of Mermis: a group of very remarkable nemas infesting insects. Journal of Parasitology 13:66-72.

Crowcroft, P.W. 1947. Notes on the occurrence of the nematode Mermis nigrescens Dujardin and its effect on the common earwig in Tasmania. Papers and Proceedings of the Royal Society of Tasmania 1947:59-62

Ferris, H. 2007. Stichosomida. McGraw-Hill Encyclopedia of Science & Technology. http://accesscience.com/abstract.aspx

Kumar, D., Nagal, P., Sidhu, H.S., Ranga, P., Kumari, P. 2023. Role of Mermithid Nematodes in the Management of Agricultural and Household Insect Pests: A review. Environment and Ecology 41:2890-2899.

Presswell, B., Evans, S., Poulin, R., Jorge, F. 2015. Morphological and molecular characterization of Mermis nigrescens Dujardin, 1842 (Nematoda: Mermithidae) parasitizing the introduced European earwig (Dermaptera: Forficulidae) in New Zealand. Journal of Helminthology 89: 267-276

Tripodi, A.D. and Strange, J.P. 2018. Rarely reported, widely distributed, and unexpectedly diverse: molecular characterization of mermithid nematodes (Nematoda: Mermithidae) infecting bumble bees (Hymenoptera: Apidae: Bombus) in the USA. Parasitology 145, 1558Ã¢â‚¬â€œ1563. https:// doi.org/10.1017/S0031182018000410Wilson, W. (1971) Nematode occurrence in Ontario earwigs (Nematoda: Dermaptera). The Canadian Entomologist 103, 1045â€“1048.