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Carabus nemoralis

By Amy Bagby

Geographic Range

Bronze carabids (Carabus nemoralis) are found throughout the Northern United States, from the Southern coast of Alaska to Montana, and from Wisconsin to Maine. Additionally, these beetles can be seen from Portugal to central Kazakhstan (Lorenz, 2021). (Lorenz, 2021)

Habitat

Bronze carabids are found in woodland and forest habitats, as well as man-made areas such as parks and gardens (Muller, 2021). Also, they are sometimes found in agricultural settings as a biological control species (Pianezzola et al., 2013). (Lorenz, 2021; Pianezzola, et al., 2013)

  • Range elevation
    0 to 305 m
    0.00 to 1000.66 ft

Physical Description

These beetles are relatively large, with an average size around 24 mm. They are typically black with bronze, green, or purple tints (Anderson et al., 2000). Females of this species often appear more blue in color on the second bodily segment, also known as the thorax. Bronze carabids have filiform (meaning long, thin, and uniform in shape) antennae, a shield-like thorax, and mandibles used for grabbing and chewing. Also, they have long, thin legs for the fast capture of prey (Lorenz, 2021). (Anderson, et al., 2000; Bland and Jaques, 2010; Lorenz, 2021)

Larvae of bronze carabids are long and black, with many body segments and three distinct legs attached to the thorax. They have large mandibles and are typically only a few millimeters smaller than the adults (Erbland, 2014). (Erbland, 2014)

  • Sexual Dimorphism
  • sexes alike
  • sexes colored or patterned differently
  • Range length
    22 to 26 mm
    0.87 to 1.02 in

Development

Bronze carabids undergo complete metamorphosis. In other words, they must go through an egg, larval, pupal, and adult stage to complete their life cycle. Most ground beetles lay their eggs in soil where they will hatch into larvae, and bronze carabids are no exception. These larvae will then feed and mature until they pupate into adults, which can take several years (Newton, 2012). (Newton, 2012)

Reproduction

There is evidence of interspecific competition between males for females of similar looking species (such as Carabus auronitens), as they may be mistaken for bronze carabid females. If the female is receptive to the male they will mate, but both beetles will go on to reproduce with others of the species during the breeding season. It is not described if parents remain with their young, or what specific pheromones attract mates (Weber and Heimbach, 2001). (Weber and Heimbach, 2001)

Bronze carabids mate in spring, with larvae developing in the summer after the young hatch. However, it has been shown that surviving adult females may reproduce during the fall. Female bronze carabids will lay an average of around 30 eggs during their entire laying period. To do this, they will create a chamber in the ground with their abdomens and lay their eggs inside of it. Occasionally, abnormal temperature fluctuations may affect the amount of eggs laid per season. Sexual maturity occurs as soon as the adult beetles are active after metamorphosis (Weber and Heimbach, 2001). (Newton, 2012; Weber and Heimbach, 2001)

  • Breeding interval
    Bronze carabids usually breed once yearly in spring, but may breed again in the fall.
  • Breeding season
    The spring breeding season usually occurs from March to May, or in the case of fall breedings, sporadically from August onward.
  • Range eggs per season
    22 to 38
  • Range age at sexual or reproductive maturity (female)
    1 to 3 years
  • Range age at sexual or reproductive maturity (male)
    1 to 3 years

Lifespan/Longevity

These beetles can live as long as three years in the wild, but not all of them will survive until sexual maturity (occurring at 1-3 years) (Newton, 2021). As with many other beetle species, not all eggs will be fertilized or viable. Of the ones that are, some may die as eggs or larvae to disease, environmental events, predation, or developmental errors. After metamorphosis, the limiting factors become food availability, environmental events, and predation. In winter, bronze carabids will undergo diapause to survive the harsh elements that otherwise would be deadly (Weber and Heimbach, 2001). (Newton, 2012; Weber and Heimbach, 2001)

  • Range lifespan
    Status: wild
    0 to 3 years
  • Typical lifespan
    Status: wild
    0 to 3 years

Behavior

Bronze carabids are solitary, motile ground beetles known for being predacious in both the larval and adult stages. Their large mandibles allow for this. They are nocturnal and tend to hide during the day, so their favored spots are underneath debris like fallen wood or large rocks. Despite being night creatures, these carabids are very shiny and reflective, which makes them a lucky find for collectors. They mainly hunt and live on the ground but, like most beetles, can climb if need be (Bland and Jacques, 2010). Bronze carabids undergo diapause, or a time of halted development, underground in the winter to avoid the cold. They may do this for a few winters until they have completed their life cycle (Hodek, 2011). (Bland and Jaques, 2010; Hodek, 2011)

Home Range

Bronze carabids hail from the Palearctic ecozone. Though they are native to Europe, they have been introduced into North America and can be found in most of the Northern United States and Southern Canada with the exception of the Great Plains. (Lorenz, 2021)

Communication and Perception

Though not much research has focused on bronze carabids specifically, most insects tend to communicate through various mediums. Visual cues allow these beetles to watch for behaviors from predators, prey, and potential mates as well as to assess lighting conditions. Thigmotaxis lets them communicate through touch, with their antennae (a very strong sensory organ). Antennae also help with chemical cues such as pheromones that may be coming from other bronze carabids or predator/prey insects. Lastly, insects including bronze carabids possess small spines or hairs around their bodies called setae, which help them sense vibrations from movement and sound (NC State, 2015). (NC State, 2015)

Food Habits

Bronze carabids are largely known as generalist predators that will eat almost anything that crosses their paths. This includes other small arthropods, slugs and snails, worms, and decaying material. They were considered largely molluscivorous, but they eat a much larger variety of food than was previously considered (Fawki et al., 2003). Since they catch and eat many types of prey, they have large mandibles for grabbing and chewing, as well as long legs for quick pursuit of a meal (Bland and Jacques, 2010). (Bland and Jaques, 2010; Fawki, et al., 2003)

Earthworms are a favored food of bronze carabids, since they are most common in their diet. These beetles are very well known for eating multiple pest species of slugs (such as Arion vulgaris), and thus are commonly used for biological control. Some researchers have found, however, that slug meals are of lower nutritional quality to these beetles, which is a breakaway from being considered molluscivores (Fawki et al., 2003). (Fawki, et al., 2003)

  • Animal Foods
  • carrion
  • insects
  • terrestrial non-insect arthropods
  • mollusks
  • terrestrial worms

Predation

Bronze carabids are well camouflaged for hiding, but are still likely eaten by predators that pursue grounded insects. No specific accounts of predation on these beetles is recorded (Bland and Jacques, 2010). (Bland and Jaques, 2010)

  • Anti-predator Adaptations
  • cryptic
  • Known Predators
    • No specific known predators have been attributed to bronze carabids

Ecosystem Roles

Bronze carabids are important insects in that they are generalists. They hunt insects that humans may consider pests, as well as consume dead materials to break them down (Fawki et al., 2003). They are also predators of many types of slugs that are agricultural pests. By using these carabids as biological controls, they are provided with a food source, and they in turn rid our crops of unwanted slugs (Pianezzola et al., 2013). (Fawki, et al., 2003; Pianezzola, et al., 2013)

Mutualist Species

Economic Importance for Humans: Positive

This species benefits humans in that they are an asset in controlling pest populations of slugs in agriculture. One study found that net production of salad greens increased greatly after greenhouse and laboratory introductions of bronze carabids (Renkema et al., 2014). Another found that they are effective even in semi-field environments (Pianezzola et al., 2013). Humans also benefit from decreased pest species in nature due to the predacious nature of bronze carabids. (Pianezzola, et al., 2013; Renkema, et al., 2014)

  • Positive Impacts
  • research and education
  • controls pest population

Economic Importance for Humans: Negative

There are no known adverse effects of bronze carabids on humans.

  • Negative Impacts
  • household pest

Conservation Status

These beetles are either not under threat where they are found or not examined, and as such there is no conservation status attributed to them.

Contributors

Amy Bagby (author), Colorado State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

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

Palearctic

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

World Map

acoustic

uses sound to communicate

agricultural

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.

biodegradation

helps break down and decompose dead plants and/or animals

carnivore

an animal that mainly eats meat

carrion

flesh of dead animals.

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

detritivore

an animal that mainly eats decomposed plants and/or animals

detritus

particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).

diapause

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.

ectothermic

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

fertilization

union of egg and spermatozoan

forest

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

heterothermic

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.

hibernation

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.

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

molluscivore

eats mollusks, members of Phylum Mollusca

motile

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.

nocturnal

active during the night

oviparous

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

pheromones

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

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

scavenger

an animal that mainly eats dead animals

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

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

solitary

lives alone

suburban

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

tactile

uses touch to communicate

taiga

Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.

temperate

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).

terrestrial

Living on the ground.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

Anderson, R., D. McFerran, A. Cameron. 2000. The Ground Beetles of Northern Ireland. Belfast: 1st. Ed. Pub. Ulster Museum.

Bland, R., H. Jaques. 2010. How to Know the Insects. Long Grove, IL: Waveland Press Inc..

Erbland, M. 2014. "Bugguide-Carabus nemoralis" (On-line). Bugguide.net. Accessed July 17, 2021 at https://bugguide.net/node/view/957022/bgimage.

Fawki, S., S. Smerup Bak, S. Toft. 2003. Food preferences and food value for the carabid beetles Pterostichus melanarius, P. versicolor and Carabus nemoralis. The 11th European Carabidologist Meeting 2003 At: Aarhus, Denmark: 99-109. Accessed July 20, 2021 at https://www.researchgate.net/publication/261171431_Food_preferences_and_food_value_for_the_carabid_beetles_Pterostichus_melanarius_P_versicolor_and_Carabus_nemoralis.

Hodek, I. 2011. Adult Diapause in Coleoptera. Psyche, 2012: 1-10. Accessed July 20, 2021 at https://www.researchgate.net/publication/258382803_Adult_Diapause_in_Coleoptera.

Lorenz, W. 2021. "Carabus nemoralis O.F. Müller, 1764" (On-line). Global Biodiversity Information Facility. Accessed July 14, 2021 at https://www.gbif.org/species/8056040.

NC State, 2015. "Insect Communication" (On-line). NC State Agriculture and Life Sciences. Accessed July 20, 2021 at https://genent.cals.ncsu.edu/bug-bytes/communication/.

Newton, B. 2012. "Ground Beetles" (On-line). Kentucky Critter Files-Kentucky Insects. Accessed July 17, 2021 at https://www.uky.edu/Ag/CritterFiles/casefile/insects/beetles/ground/ground.htm.

Pianezzola, E., S. Roth, B. Hatteland. 2013. Predation by carabid beetles on the invasive slug Arion vulgaris in an agricultural semi-field experiment. Bulletin of Entomological Research, 103: 225-232. Accessed July 14, 2021 at https://web-b-ebscohost-com.ezproxy2.library.colostate.edu/ehost/detail/detail?vid=3&sid=ace41b5f-93a1-40f4-8b2c-78e1ae8a82ce%40sessionmgr102&bdata=JkF1dGhUeXBlPWNvb2tpZSxpcCx1cmwsY3BpZCZjdXN0aWQ9czQ2NDA3OTImc2l0ZT1laG9zdC1saXZl#AN=85740364&db=aph.

Renkema, J., G. Cutler, A. Hammermeister. 2014. Using ground beetles (Coleoptera: Carabidae) to control slugs (Gastropoda: Pulmonata) in salad greens in the laboratory and greenhouse. The Canadian Entomologist, 146(05): 567-578. Accessed July 20, 2021 at https://www.researchgate.net/publication/269366538_Using_ground_beetles_Coleoptera_Carabidae_to_control_slugs_Gastropoda_Pulmonata_in_salad_greens_in_the_laboratory_and_greenhouse.

Weber, F., U. Heimbach. 2001. Behavioural, reproductive and developmental seasonality in Carabus auronitens and Carabus nemoralis (Col., Carabidae). Mitteilungen aus der Biologischen Bundesanstalt für Land- und Forstwirtschaft Berlin-Dahlem, 382: 1-194. Accessed July 20, 2021 at https://www.researchgate.net/publication/261673139_Behavioural_reproductive_and_developmental_seasonality_in_Carabus_auronitens_and_Carabus_nemoralis_Col_Carabidae.

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