Mermis nigrescens

Geographic Range

Mermis nigrescens is reported from many locations in North America and Europe. Related species are known from Africa. (Christie, 1937; Webster and Thong, 1984)


Adults of Mermis nigrescens live buried in the soil, while larva live as parasites inside grasshoppers. The species is more frequently found in grasslands, meadows, clearings, and other well-vegetated but not tree-covered habitats. (Christie, 1937)

Physical Description

This is a large species of nematode. Adult males range from 40 to 50 mm long, while the females range from 80 to 200 mm long. The body of the worm tapers in the front, with the head slightly offset and rounded in the front. Larvae and adult males are generally cream colored, as are females if their uterus is empty. If the uterus contains eggs, the female will appear brownish or black because of the coloration of the eggs she contains. Males have two spicules, one of which is used in reproduction. Both sexes possess two laterally-placed anterior chemoreceptors called amphids, but they lack posterior phasmids. Both sexes also possess a terminal mouth with two lateral papillae close to it and four head papillae further back.

In adult females, there is an orange/red area behind the head, which is associated with a unique light sensitive organ. Mohammed et al (2007) give details of the structure and function of this organ. It serves to allow the female to know where to go when laying eggs. (Christie, 1937; Mohammed, et al., 2007; Webster and Thong, 1984)

  • Sexual Dimorphism
  • female larger
  • sexes colored or patterned differently
  • sexes shaped differently
  • Range length
    40 to 200 mm
    1.57 to 7.87 in


Embryos begin to develop in the eggs while still in the female. By the time the eggs are laid (in late spring or early summer) the offspring are already stage 2 larvae. If an egg is ingested by a grasshopper or other orthopteran, the outer layer of the egg rubs off and within minutes the larva begins to move out of the inner shell.

Once hatched, the larva pierces the gut wall of the host and enters the body cavity. Larval worms feed on host body fluids and tissues and grow. They emerge from the host in approximately 3-6 weeks. The worms develop faster in warmer temperatures. Size and species of hosts affects developmental time, and larval worms stay longer and grow larger in mature adult hosts than in nymph or young adult hosts. Female worms tend to remain in the host longer than males, and are larger at emergence than males. Worms puncture the host body wall and emerge as 4th stage larvae (the host and any remaining worms die). They crawl 15-20 cm into the soil where they molt, become mature adults and mate. Males die after mating. Females spend the winter in diapause in the soil and emerge on rainy or dew mornings in the following spring/summer to climb up on to plants and lay their eggs. (Christie, 1937; Webster and Thong, 1984)


Males mate with many females, while the female will only mate with one male. Males have a flexible tail including one of the spicules which they use to wrap around the female and hold the female in place during copulation. (Christie, 1937)

After spending the winter in the soil, emerge in the late spring or early summer on damp or rainy mornings, and climb on the leaves of plants, usually 30-60 cm above soil level and lay thousands of dark brown eggs on the leaves. The eggs are attached with threads of adhesive.

Eggs from unmated females have been found to be viable, so apparently parthenogenesis is possible in this species. (Christie, 1937; Webster and Thong, 1984)

  • Breeding interval
    Breed once yearly
  • Breeding season
  • Range number of offspring
    2000 (low)
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    1 years

No parental care is provided after eggs are laid. Females provision the eggs with a coating that protects them from sunlight damage, and glue to hold them onto leaves. (Christie, 1937; Webster and Thong, 1984)

  • Parental Investment
  • pre-fertilization
    • protecting
      • female


Most Mermis nigrescens complete their lifecycle in one year, but in the absence of rains or other moisture to trigger egg-laying, females can persist in the soil for 2-3 years. Females die shortly after climbing out of the soil to lay eggs. (Chapman, et al., 1990; Christie, 1937; Webster and Thong, 1984)

  • Range lifespan
    Status: wild
    3 (high) years
  • Typical lifespan
    Status: wild
    1 (high) hours


The larvae of M. nigrescens are endoparasitic. During their larva stages they infect the body cavity of grasshoppers. They may be located anywhere within the host's hemocoel. Once juveniles burrow out of a host, they will dig into the soil where they molt into adults. They are dormant in the winter.

The action of females crawling on plants in order to deposit their eggs on vegetation above ground is considered an important behavior modification for insect parasitism, and is an unusual behavior in nematodes. Most nematodes will move away from light, but adult females of this species are positively phototaxic when laying eggs. (Atkins, 2004; Belovsky, et al., 2000; Mohammed, et al., 2007)

Home Range

This species does not have a home range.

Communication and Perception

Little is known about communication in this species. It is likely to be based on touch and chemo-sensing. These worms can sense chemicals, touch, and moisture, and adult females have an unusual (for nematodes) light-sensing structure. (Christie, 1937; Mohammed, et al., 2007; Webster and Thong, 1984)

Food Habits

Larva feed on amino acids, lipids, and carbohydrates from the hemolymph of the host. The free-living adults do not eat. (Atkins, 2004; Belovsky, et al., 2000)

  • Animal Foods
  • body fluids


The predators of this species are unknown, but likely include predators of soil invertebrates, such as carabid beetles, centipedes, and shrews. (Belovsky, et al., 2000)

Ecosystem Roles

Larva of this nematode are parasites of orthopteran insects, and can sometimes have substantial effects on host populations. (Atkins, 2004; Belovsky, et al., 2000; Webster and Thong, 1984)

Species Used as Host

Economic Importance for Humans: Positive

These worms could potentially be used as control agents for pest grasshoppers. However, nematode ecology is poorly understood, especially in nature. (Belovsky, et al., 2000; Chapman, et al., 1990; Webster and Thong, 1984)

Economic Importance for Humans: Negative

Normally these worms have no known adverse effects on humans. There are a very small number of cases of M. nigrescens finding its way into humans, but this is extremely rare. Poinar and Hoberg (1988) describe a case where a female was found in an infant's mouth, and give references to the few similar cases. (Poinar, Jr. and Hoberg, 1988)

Conservation Status

The status of populations of this species are unknown, but it is not believed to require special conservation. The species has not been rated by the IUCN, or other agencies.


George Hammond (author, editor), Animal Diversity Web.



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map


living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map


living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat


Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.


uses smells or other chemicals to communicate


active at dawn and dusk


a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.

  1. active during the day, 2. lasting for one day.

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


union of egg and spermatozoan


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.


the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

internal fertilization

fertilization takes place within the female's body


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death


development takes place in an unfertilized egg


chemicals released into air or water that are detected by and responded to by other animals of the same species


having more than one female as a mate at one time


"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

seasonal breeding

breeding is confined to a particular season


remains in the same area


offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.


reproduction that includes combining the genetic contribution of two individuals, a male and a female


lives alone


living in residential areas on the outskirts of large cities or towns.


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.


A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.


uses sight to communicate


Atkins, W. 2004. Adenophorea (Roundworms). Pp. 283-291 in M Hutchins, D Thoney, M McDade, eds. Grzimek's Animal Life Encyclopedia, Vol. Vol. 1: Lower Metazoans and Lesser Deuterostomes, 2nd Edition. Detroit, Michigan, USA: Gale. Accessed January 29, 2009 at

Belovsky, G., D. Branson, J. Chase, J. Barker, G. Hammond. 2000. "Mite and Nematode Parasites of Grasshoppers" (On-line). Accessed November 25, 2007 at

Chapman, R., A. Joern, D. Streett, M. McGuire. 1990. The Biology of Grasshoppers. New York: Wiley-Interscience.

Christie, J. 1937. Mermis nigrescens, a Nematode Parasite of Grasshoppers. The Journal of Agricultural Research, Volume 55 Issue 5: 353-364.

Mohammed, A., C. Burr, A. Burr. 2007. "Unique Two Photoreceptor Scanning Eye of the nematode Mermis nigrescens" (On-line). Accessed November 25, 2007 at

Poinar, Jr., G., E. Hoberg. 1988. "Mermis Nigrescens (Mermithidae: Nematoda) Recovered from the Mouth of a Child" (On-line). Accessed November 25, 2007 at

Webster, J., C. Thong. 1984. Nematode Parasites of Orthopterans. Pp. 697-721 in W Nickle, ed. Plant and Insect Nematodes. New York City, New York, USA: Marcel Dekker Inc..