''Acronicta rumicis'', the knot grass moth, is a
species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of
moth
Moths are a group of insects that includes all members of the order Lepidoptera that are not Butterfly, butterflies. They were previously classified as suborder Heterocera, but the group is Paraphyly, paraphyletic with respect to butterflies (s ...
which is part of the
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
''
Acronicta
''Acronicta'' is a genus of noctuid moths containing about 150 species distributed mainly in the temperate Holarctic, with some in adjacent subtropical regions. The genus was erected by Carl Linnaeus in his 1758 10th edition of Systema Naturae, ...
'' and family
Noctuidae
The Noctuidae, commonly known as owlet moths, cutworms or armyworms, are a family (biology), family of moths. Taxonomically, they are considered the most controversial family in the superfamily Noctuoidea because many of the clades are constantly ...
. It was
first described by
Carl Linnaeus
Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...
in his 1758
10th edition of ''Systema Naturae''. It is found in the
Palearctic
The Palearctic or Palaearctic is a biogeographic realm of the Earth, the largest of eight. Confined almost entirely to the Eastern Hemisphere, it stretches across Europe and Asia, north of the foothills of the Himalayas, and North Africa.
Th ...
region. ''A. rumicis'' lives and feeds on plants located in wide-open areas. At its larval stage, as a caterpillar, it causes such a large impact as a crop pest that it has received much attention and research. ''A. rumicis'' feeds on maize, strawberries and other herbaceous plants.
The moth's evolution has been affected by the
industrial melanism
Industrial melanism is an evolutionary effect prominent in several arthropods, where dark pigmentation (melanism) has evolved in an environment affected by industrial pollution, including Sulfur dioxide, sulphur dioxide gas and dark soot deposit ...
that occurred in Europe during the late 19th and early 20th centuries, causing a dramatic increase in two aberrations (''salicin'' and ''lugubris''), which have darker grey wings. Today, ''A. rumicis'' is important to conservation efforts in the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...
, because, like many other species, it is in decline. However, as it is part of a UK Priority
Biodiversity Action Plan and receiving greater awareness and conservation, the species may become more abundant.
Description and identification
''A. rumicis'' has a wingspan of 34–44 mm. The forewings are blotched with a mixture of dark and light-grey shades, while the hindwings are dark brown.
[Alford, D. V., 2014. ''Pests of Fruit Crops: A Colour Handbook''. p.356.] A white spot is seen midway down the trailing edge of the forewing providing a distinct marker for ''A. rumicis'' not seen in other ''Acronicta'' moths. Chinese and Japanese moths tend to be larger than their European counterparts. The Asian moths also have lower forewings that have darker shades of grey.
Technical description and variation
''C. rumicis'' L. (3i). Forewing dark grey, varied in places with whitish; lines and shades black; outer line marked by a white spot on the
submedian fold; hindwings brownish fuscous Larva marbled dark and light grey: a dorsal row of red spots on black blotches, and a row of white spots on each side; a pale line below spiracles, containing orange-red tubercles; segments 5 and 12 of dorsum humped; tubercles with fascicles of fuscous and fulvous hairs— ''turanica'' Stgr., a form from Central Asia, is much paler, with the hindwings whitish. — Chinese and Japanese examples (3k) are larger than European and in all cases darker; in particular the lower half of forewing is blacker and the white spot of outer line then often obscured; possibly the scotch form figured by Curtis as ''salicis'', a melanic form, may represent this aberration, though the larva figured as belonging thereto is unquestionably that of ''menyanthidis''. — ab. ''alnoides'' Geest (3k) has the costal half of forewing grey, the inner half blackish, somewhat interrupted with a strong black dagger-shaped mark at base and above anal angle; superficially resembles a dark grey alni; recorded from Freiburg in Baden. — ab. ''euphorbiae'' Steph. nec. Hbn. is grey brown, with the stigmata and space between them pale; and ab. ''euphrasiae'' Steph. nec Dup. is pale yellowish grey with numerous black lines and the orbicular stigma faint or obsolete, occurring in Cornwall.
Taxonomy and phylogenetics
''A. rumicis'' is a moth of the genus ''Acronicta'' and family Noctuidae. Noctuidae has upwards of 21,000 species. Noctuids are commonly known as "owlet moths" because of their large eyes that shine in the dark and the colour of their wings which make them difficult to see. In their usual resting position, noctuids fold their wings back over their bodies; the forewings overlap one another. The closed wings form a tent-like shape. Almost all ''Acronicta'' larvae are brightly coloured with spiky brown hairs all along the dorsal side of the body.
[Chapman, T.A., 1890. The Genus ''Acronycta'' and its Allies. ''The Entomologist's Record and Journal of Variation'', 1(April), pp.1–4, 26–28.] According to
Thomas Algernon Chapman, the genus ''Acronicta'' can be split into three major groups: The first, characterized by a hoop-like structure of the pupa and clumped oviposition, includes: ''
A. auricoma'', ''
A. myricae'', ''
A. menthanthidis'', ''
A. venosa'', and ''
A. rumicis''. The second, characterized by terminal spines of pupa and dome-shaped ova laid apart from others, includes: ''
A. psi'', ''
A. tridens'', ''
A. strigosa'', ''
A. alni'', ''
A. megacephala'', ''
A. leporina'', ''
A. aceris''. The third group has only one species, ''
A. ligustri''.
Distribution and habitat
''A. rumicis'' is distributed throughout the
Palearctic
The Palearctic or Palaearctic is a biogeographic realm of the Earth, the largest of eight. Confined almost entirely to the Eastern Hemisphere, it stretches across Europe and Asia, north of the foothills of the Himalayas, and North Africa.
Th ...
. It is common in
northwestern China
Northwestern China () is a region in the People's Republic of China. It consists of five provincial administrative regions, namely Shaanxi, Gansu, Qinghai, Ningxia, and Xinjiang.
The region is characterized by a (semi-)arid continental climate. ...
, the
Korean Peninsula
Korea is a peninsular region in East Asia consisting of the Korean Peninsula, Jeju Island, and smaller islands. Since the end of World War II in 1945, it has been politically divided at or near the 38th parallel between North Korea (Dem ...
, and
Japan
Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...
, although it has also been found in other parts of
Eurasia
Eurasia ( , ) is a continental area on Earth, comprising all of Europe and Asia. According to some geographers, Physical geography, physiographically, Eurasia is a single supercontinent. The concept of Europe and Asia as distinct continents d ...
, including
Russia
Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
. ''A. rumicis'' is found in almost all parts of
Europe
Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
, though it is absent in some areas of north-western
Scandinavia
Scandinavia is a subregion#Europe, subregion of northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. ''Scandinavia'' most commonly refers to Denmark, Norway, and Sweden. It can sometimes also ...
. There has been much research about the species in
England
England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...
and
Scotland
Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...
.
These moths tend to spend their lives in plants located in wide-open areas like meadows, woodland clearings, gardens, and hedgerows, generally in non-humid areas.
[Winiarska, G., 1990. Communities of noctuids (Lepidoptera, Noctuidae) of linden-oak-hornbeam forests of the Mazovian Lowland. ''Fragmenta Faunistica'', 15(11), pp.143–163.
]
Food resources
Caterpillars
At the caterpillar stage, ''A. rumicis'' tends to feed on low-growing, herbaceous plants, including sorrel, dock, bramble, thistles, hop, and occasionally on the leaves of shrubs.
In addition, ''A. rumicis'' larvae favour fruit trees like ''
Prunus
''Prunus'' is a genus of flowering plant, flowering trees and shrubs from the family (biology), family Rosaceae. The genus includes plums, cherries, peaches, nectarines, apricots and almonds (collectively Drupe, stonefruit). The genus has a cosm ...
'' species and plants of the family
Polygonaceae
The Polygonaceae are a Family (biology), family of flowering plants known Common name, informally as the knotweed family or smartweed—buckwheat family in the United States. The Botanical name, name is Basionym, based on the genus ''Polygonum'', ...
.
[Cho, Y., Kwon, O. & Nam, S.-H., 2006. Ecological and morphological characteristics of the endoparasitoids of larval ''Acronicta rumicis'' (Lepidoptera: Noctuidae). ''Entomological Research'', 36, pp. 208–215.]
In research, one of the most commonly used host plants is ''
Rumex obtusifolius
''Rumex obtusifolius'', commonly known as bitter dock, broad-leaved dock, bluntleaf dock, dock leaf, dockens or butter dock, is a perennial plant in the family Polygonaceae. It is native to Europe, but is found on all temperate continents. It i ...
'', a herbaceous plant commonly found within ''A. rumicis'' range.
Parental care
Oviposition

Females tend to lay eggs on leaves of host plants in large clusters. The eggs have long longitudinal ridges, which originate and spread out from the
micropylar area of the egg. The longest ridges tend to be in a zigzag formation.
[Dolinskaya, I. V., 2014]
Egg Morphology of some Noctuidae (Lepidoptera)
''Vestnik Zoologii'', 48(4), pp. 353–364. The eggs have a flattened shape, making clustering and clumping easier.
Life history
''A. rumicis'' species generally have two broods: the first generation flies in May and June, while the second flies in August and September. However, the number of generations can differ based on location; in southern Europe, it tends to have three broods, while in the north, it has only one, most likely due to
diapause
In animal dormancy, diapause is the delay in development in response to regular and recurring periods of adverse environmental conditions.Tauber, M.J., Tauber, C.A., Masaki, S. (1986) ''Seasonal Adaptations of Insects''. Oxford University Press It ...
.
The number of broods may be determined by the duration of light and temperature ranges. The larvae tend to feed from the summer onwards until winter, during which ''A. rumicis'' spend its time in the pupae stage in cocoons.
Egg
Eggs are laid in clusters, in almost regular, overlapping rows on host plants. The egg stage lasts about 5 to 10 days. The eggs have a round flattened shape like a sand dollar and has a
micropylar area that has 20 long ridges that radiate from the center, almost like a child's drawing of a sun and its rays.
The flattened structure allows for stability while resting on the host plant.
Caterpillar
When larvae hatch, they tend to nibble out the round opening of the egg. Usually, ''A. rumicis'' larvae are ready to pupate after 30 days. They tend to be about 40 mm long, having dark brown bodies, with white spots along both sides of the body and red spots along the centre of the back. Body hairs grow in
tufts
Tufts University is a private research university in Medford and Somerville, Massachusetts, United States, with additional facilities in Boston and Grafton, as well as Talloires, France. Tufts also has several Doctor of Physical Therapy progr ...
, arranged in rows: two rows along each side of the body and one row along the centre of the back.
Pupa
Once the winter months near, fully grown caterpillars pupate in cocoons on leaves or leaf litter. The cocoon has tough white silk with one simple layer of grass, twigs, or leaves for better concealment from predators.
Adult
Adult moths tend to emerge in June but can also appear in earlier months if the weather is consistently warm.
Enemies
Predators
Although the general cause of trouble in the life of ''A. rumicis'' is parasitism via
parasitoid
In evolutionary ecology, a parasitoid is an organism that lives in close association with its host (biology), host at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major evolutionarily stable str ...
s, another group of predators includes small birds. These birds, like the
great spotted woodpecker
The great spotted woodpecker (''Dendrocopos major'') is a medium-sized woodpecker with pied black and white plumage and a red patch on the lower belly. Males and young birds also have red markings on the neck or head. This species is found acros ...
, tend to breed and nest in agricultural regions. In one study from Slovenia, the birds were nested in a hop field.
Hop is a popular food resource for ''A. rumicis'', while caterpillars are the primary food source for these birds.
Parasites
Parasitism in ''A. rumicis'' generally occurs in the months of May and October. Rates are lower in the months of June and July for reasons yet unknown. Most parasitoids affecting ''A. rumicis'' are
parasitic wasp
Parasitoid wasps are a large group of hymenopteran superfamilies, with all but the wood wasps ( Orussoidea) being in the wasp-waisted Apocrita. As parasitoids, they lay their eggs on or in the bodies of other arthropods, sooner or later causi ...
s in the
Braconidae
The Braconidae are a family of parasitoid wasps. After the closely related Ichneumonidae, braconids make up the second-largest family in the order Hymenoptera, with about 17,000 recognized species and many thousands more undescribed. One analysis ...
and
Ichneumonidae
The Ichneumonidae, also known as ichneumon wasps, ichneumonid wasps, ichneumonids, or Darwin wasps, are a family of parasitoid wasps of the insect order Hymenoptera. They are one of the most diverse groups within the Hymenoptera with roughly 25 ...
families, as well as parasitic flies.
One of the most common parasitoids of ''A. rumicis'' is ''
Glyptapanteles liparidis'', a larval parasitoid that is highly distributed throughout
Eurasia
Eurasia ( , ) is a continental area on Earth, comprising all of Europe and Asia. According to some geographers, Physical geography, physiographically, Eurasia is a single supercontinent. The concept of Europe and Asia as distinct continents d ...
.
[CHO, Y.-H., NAM, S.-H. & KWON, O., 2006. Interaction of ''Acronicta rumicis'' (Lepidoptera: Noctuidae) and its larval parasitoid, ''Glyptapanteles liparidis'' (Hymenoptera: Ichneumonidae). ''Entomological Research'', 36, pp. 79–84.] ''G. liparidis''
oviposit
The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typical ...
s on the surface of the moth larvae; once hatched, the wasp larvae feed on the ''A. rumicis'' larvae and eventually cause death.
Based on one study in South Korea, ''G. liparidis'' affects ''A. rumicis'' in its first, second, third, and fourth
instar
An instar (, from the Latin '' īnstar'' 'form, likeness') is a developmental stage of arthropods, such as insects, which occurs between each moult (''ecdysis'') until sexual maturity is reached. Arthropods must shed the exoskeleton in order to ...
.
The same study also discovered that the second-instar larvae were apparently the best food source for this parasitoid, as the second-instar larvae had the highest mortality rate in comparison to the other three larval stages. As the ''G. liparidis'' continuously grows and utilizes the resources produced internally by ''A. rumicis'' larvae, the feeding habits of these larvae change as well. On average, parasitized larvae consume more plant material than those not parasitized; the second instar larvae tend to consume the most food in comparison to the first, third, and fourth instars, supporting the idea that most ''G. liparidis'' feed most efficiently on the second instar larvae of ''A. rumicis''.
Genetics of colour patterns
Pigmentation and structural colouration
Industrial melanism
Industrial melanism is an evolutionary effect prominent in several arthropods, where dark pigmentation (melanism) has evolved in an environment affected by industrial pollution, including Sulfur dioxide, sulphur dioxide gas and dark soot deposit ...
exists within the species, meaning the moths evolved during the industrial period in
England
England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...
when dark soot was deposited into the environment. The aberration ''salicis'' Curtis, which is commonly found throughout the moth's distribution range, has darker grey-blotched sections on wings and retains the ''A. rumicis'' identifying marker, the white spot on its forewings. Aberration ''salicis'' is commonly found distributed in England,
Wales
Wales ( ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by the Irish Sea to the north and west, England to the England–Wales border, east, the Bristol Channel to the south, and the Celtic ...
, and
Ireland
Ireland (, ; ; Ulster Scots dialect, Ulster-Scots: ) is an island in the North Atlantic Ocean, in Northwestern Europe. Geopolitically, the island is divided between the Republic of Ireland (officially Names of the Irish state, named Irelan ...
.
The aberration ''lugubris'' Schultz is almost completely black, lacking the mixed-grey mottling on the wings, but still retains the prominent white spot marker on its forewings.
[West, B.K., 2005. ''Acronicta rumicis'' L. ( Lep.: Noctuidae) extreme melanic ab. ''lugubris'' Schultz in Kent, and continued decline in melanism. ''Entomologist's Record and Journal of Variation'', 2005(4), pp. 174–175.] Aberration ''lugubris'' can be found mainly in England. According to B.K. West, since the late 1990s, melanism in ''A. rumicis'' has become less and less prevalent; in 1995, about 20% of ''A. rumicis'' were observed to be melanic, but over the course of five years the percentage decreased to 6.1%. By 2004, only 2.8% of population were melanic.
With the industrial period in the past and resting surfaces less darkened by soot, it is reasonable to see that evolutionarily, the melanic variations are no longer as favourable.
Physiology
Diapause
In ''A. rumicis'', duration of light and temperature are two major factors causing
diapause
In animal dormancy, diapause is the delay in development in response to regular and recurring periods of adverse environmental conditions.Tauber, M.J., Tauber, C.A., Masaki, S. (1986) ''Seasonal Adaptations of Insects''. Oxford University Press It ...
, the slowing or stopping of development in an insect when environmental conditions are not optimal. In one study, the onset of diapause was observed after varying photoperiods, while constantly rearing ''A. rumicis'' larvae at 27-28 °C. When ''A. rumicis'' were exposed to light on a short day, or 6–15 hours in the experiment, during the larval feeding period, almost all individuals underwent diapause after reaching pupal stage.
[Lee, A.D., 1955. ''The Physiology of Diapause in Arthropods'' 4th ed., Cambridge Monographs in Experimental Biology.] As the daily photoperiods extended past 17 hours, the incidence of diapause began to drop, not causing any change to the development of the pupae in the cocoon.
The ability of ''A. rumicis'' to undergo diapause allows for the completion of two generations while its host plants are available.
[Saulich, A.K., Sokolova, I. V & Musolin, D.L., 2015]
Seasonal development of the dark spectacle ''Abrostola triplasia'' (L.) (Lepidoptera, Noctuidae) and its environmental control
''Entomological Review'', 95(6), pp. 687–692. The first generation develops under longer photoperiods, therefore the pupae are physiologically active, while the second generation grow under shorter photoperiods, meaning it is more beneficial for pupae to form diapause as they overwinter through the cold.
Interactions with humans
Pests of crop plants
''A. rumicis'' is a minor pest of various of fruit plants, mostly strawberries. However, they can also cause damage to blackberry, raspberry, loganberry, apple, pear, and cherry. Usually the larvae cause defoliation as they feed on the newly grown leaves.
''A. rumicis'' also attacks beans, ground nuts, wheat, maize,
brassica
''Brassica'' () is a genus of plants in the cabbage and mustard family (Brassicaceae). The members of the genus are informally known as cruciferous vegetables, cabbages, mustard plants, or simply brassicas. Crops from this genus are sometim ...
s, and others.
According to a study in Poland, ''A. rumicis'' has also taken over maize populations, feeding until the leaves of the corn plants are no longer fresh and new because of the shift into harvesting season. During the spring and summer, the larvae of these moths damages both the leaves and silks of the cobs, occasionally eating soft kernels as well. When the second brood came in the fall, they only ate the leaves. This study in Poland further supports that ''A. rumicis'' larva prefer to eat fresh and newly grown leaves.
Conservation
Overall, the population of ''A. rumicis'' is in a sharp decline. Focusing on the moths in the United Kingdom, current research suggests that moths are in danger due to habitat loss, poor habitat management, global warming, and environmental deterioration from pesticides and pollution.
[Coulthard, E., 2015. ''Habitat and landscape-scale effects on the abundance and diversity of macromoths (Lepidoptera) in intensive farmland''. The University of Northampton.] Since 1969, the population of ''A. rumicis'' has declined by nearly 75%. Recently, ''A. rumicis'' was assigned as a Priority
Biodiversity Action Plan (BAP) species, meaning the moth was identified as most threatened and will immediately be part of conservation efforts.
[Anon, 2016. UK BAP priority species. ''Joint Nature Conservation Committee''.]
Researchers are realizing that the conservation of woodland areas is a high priority, in order to sustain as many populations of BAP species as possible; they also found a positive correlation between the species richness of herbaceous plants and the population density of moths.
Habitat loss and migration issues

According to Emma Coulthard,
hedgerow
A hedge or hedgerow is a line of closely spaced (3 feet or closer) shrubs and sometimes trees, planted and trained to form a barrier or to mark the boundary of an area, such as between neighbouring properties. Hedges that are used to separate ...
s in close proximity to crop plants and farmlands are highly important to the survival of moths like ''A. rumicis''. Habitats like hedgerows tend to provide food resources, shelter, and a place for females to lay eggs. In addition, recent studies have shown that hedgerows may act as guides for moths when flying from one location to another. As moths are nocturnal, it is highly unlikely that they use visual aids as guides, but rather are following olfactory markers.
However, recently, hedgerows have been removed to increase agricultural efficiency. Removing key habitats like hedgerows not only limits the basic necessities of survival (i.e. food, shelter), but also prevents the moth from navigating properly; eventually, the moth would lose its trail and then potentially die.
Even the smallest gaps between two bunches of hedgerows can cause a moth to go astray; one metre of no hedgerow can make an impact.
Therefore, it is crucial for agriculturalists to figure out a way to pursue their plans while conserving the homes of moths like ''A. rumicis''.
References
* ''The flight season refers to the
British Isles
The British Isles are an archipelago in the Atlantic Ocean, North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner Hebrides, Inner and Outer Hebr ...
. This may vary in other parts of the range.''
External links
Fauna EuropaeaLepiforim.deUK MothsVideo about the Knott Grass Moth's caterpillar
{{Taxonbar, from=Q474590
Acronicta
Moths described in 1758
Moths of Africa
Moths of Asia
Moths of Europe
Moths of the Middle East
Taxa named by Carl Linnaeus