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Arctia virginalis

By Claire Walther

Geographic Range

Ranchman's tiger moths, although relatively well distributed throughout western North America, tend to have local and sporadic populations, and can be uncommon in most of their range. The species ranges from southern British Columbia into southern California, Monterrey Bay area. In the United States it can be found throughout the Pacific Northwest and across the Cascades into Nevada, Utah and Colorado. ("Arctia virginalis (Boisduval, 1852)", 2021)

Habitat

Ranchman's tiger moths have sporadic populations through the western United States, often in low elevations and riparian zones, meadows, lowland prairie and forests. Although they can be found in regions characterized by deserts, they will only live around streams, creeks, or other bodies of water.

Their preferred habitat, which holds the strongest local populations, occurs in marshy wetlands with large stands of their preferred hostplant, bush lupine (Lupinus arboreus). ("Arctia virginalis (Boisduval, 1852)", 2021; Grof-Tisza, et al., 2017)

Physical Description

The ranchman's tiger moth boasts bold colors throughout all life stages. As a caterpillar, the moth is covered head to rear in long hairs, typically black in the middle and red on each end, sometimes completely rusty red, with long white tufts also sprouting from the midsection of its body.

Adults have distinct forewings, black with bright cream to yellow spotting. The hindwings are bright as well, orange with black spots, matching the striped orange and black abdomen and orange head. Although color and patterning varies slightly, some with more black than orange on their hindwings, for example, this moth is typically easy to identify.

This species is considered large compared to other tiger moths, with forewings spanning 2.6 to 3.1 cm. ("Arctia virginalis (Boisduval, 1852)", 2021; "Species Arctia virginalis - Ranchman's Tiger Moth - Hodges#8163", 2021)

  • Average length
    3.8 - 5 cm
    in
  • Average wingspan
    2.6 - 3.1 cm
    in

Development

Although not much is known about the behavior of the ranchman's tiger moth, the species undergoes complete metamorphosis. Beginning from small, yellow-green eggs, these tiger moths likely transition through 5 instars as caterpillars, as other members of the family Erebidae do. This species overwinters as larvae, with small caterpillars hatching in summer and pausing development until spring. (Grof-Tisza, et al., 2017; "Ranchman's Tiger Moth (Platyprepia virginalis)", 2021)

Reproduction

Ranchman's tiger moths display a unique habit called "hill-topping" during the mating season. Although hill-topping occurs in other insect groups, it is uncommon in moths. Hill-topping occurs when groups of animals congregate on a hilltop in order to find one another. This increases the chances that males and females of the same species will be able to find and mate with one another. Besides this habit, little is known about adult ranchman's tiger moths. (Grof-Tisza, et al., 2017)

Adult female ranchman's tiger moths will lay clutches of eggs on or near larval hostplants throughout the summer. The caterpillars will hatch out a few weeks after being laid, however, they will not develop much until the spring. This means they spend the winter as tiny larvae in the leaf litter, and begin to grow and develop in March to April of the next year. Late instar caterpillars can continue feeding through the winter. Not much is known about the adult life stage. (Grof-Tisza, et al., 2017; Karban, et al., 2010)

  • Breeding interval
    Ranchman's tiger moths mate and lay eggs once per year.
  • Breeding season
    Adult moths breed between June and August.

Like other moths, this species does not display any parental care of its young.

  • Parental Investment
  • no parental involvement

Behavior

The adult ranchman's tiger moths are typically active from June through August in the majority of their range. Caterpillars are present from summer through the spring of the following year. Although they seem to live solitarily, they are known to congregate on hilltops to find mates, a habit called hill-topping. The adults are diurnal, and relatively short-lived. (Grof-Tisza, et al., 2017; "Species Arctia virginalis - Ranchman's Tiger Moth - Hodges#8163", 2021)

Communication and Perception

Not much is known about the communication strategies of adult ranchman's tiger moths.

Food Habits

The ranchman's tiger moth is a food generalist, feeding on the foliage of a variety of herbaceous plants including hemlock (Family: Apiaceae), seaside daisy plants (Erigeron glaucus), and bush lupine (L. arboreus). Studies show they have higher survival rates when feeding solely on bush lupine than solely on another plant. However, studies also show that a mixed diet increases survival even more, and these caterpillars are known to feed on multiple species of plant in one day. (Grof-Tisza, et al., 2017; Karban, et al., 2010; "Ranchman’s Tiger Moth (Platyprepia virginalis)", 2016)

  • Plant Foods
  • leaves

Predation

Although it is likely there are many opportunistic predators of ranchman's tiger moths, such as birds or assassin bugs, the only documented predators are ants (Formicidae) and parasitoid tachinid flies (Thelaira americana).

To defend themselves from predators, both caterpillars and adult moths display aposematic coloration as a warning. They are also covered in long hairs to deter potential predators, and protect their bodies. Additionally, their preferred habitat helps protect young caterpillars, as ant attacks are less common when the hostplant is situated in a marshy area. Finally, these caterpillars will use a diet change to help protect themselves from fly parasitoids. Studies show that when a caterpillar becomes parasitised, it is more likely to eat hemlock than lupine, and has a higher chance of surviving the fly when it does so. (Grof-Tisza, et al., 2017; Karban, et al., 2010)

Ecosystem Roles

More research needs to be done into the ecosystem roles of this species.

Commensal/Parasitic Species

Economic Importance for Humans: Positive

There is an aesthetic value associated with this recognizable caterpillar and moth, and many insect enthusiasts enjoy observing or preserving them for collections. ("Ranchman’s Tiger Moth (Platyprepia virginalis)", 2016)

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

This species has no known negative impact on humans or economics. Although they are herbivores, their populations are never dense enough to be considered a pest on their hostplants.

However, caution should be taken if attempting to handle caterpillars of this species as the hairs of related species can cause mild skin irritation. (Karban, et al., 2010)

Conservation Status

There is no special status for this species.

Other Comments

The ranchman's tiger moth has two synonymous scientific names, Arctia virginalis and Platyprepia virginalis. Although the genus Platyprepia is still widely used, the moth was moved into Arctia, and is therefore used in this species account.

Contributors

Claire Walther (author), Special Projects, 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

aposematic

having coloration that serves a protective function for the animal, usually used to refer to animals with colors that warn predators of their toxicity. For example: animals with bright red or yellow coloration are often toxic or distasteful.

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.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

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.

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

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

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

forest

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

herbivore

An animal that eats mainly plants or parts of plants.

marsh

marshes are wetland areas often dominated by grasses and reeds.

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.

motile

having the capacity to move from one place to another.

oviparous

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

polymorphic

"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.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

semelparous

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.

sexual

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

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

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).

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.

savanna

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.

References

2021. "Arctia virginalis (Boisduval, 1852)" (On-line). Pacific Northwest Moths. Accessed October 05, 2021 at http://pnwmoths.biol.wwu.edu/browse/family-erebidae/subfamily-arctiinae/tribe-arctiini/arctia/arctia-virginalis/.

2021. "Ranchman's Tiger Moth (Platyprepia virginalis)" (On-line). Insect Identification. Accessed October 05, 2021 at https://www.insectidentification.org/insect-description.php?identification=Ranchmans-Tiger-Moth.

Missoula Butterfly House and Insectarium. 2016. "Ranchman’s Tiger Moth (Platyprepia virginalis)" (On-line). Missoula Butterfly House. Accessed October 05, 2021 at https://www.missoulabutterflyhouse.org/ranchmans-tiger-moth-platyprepia-virginalis/.

Iowa State University Department of Entomology. 2021. "Species Arctia virginalis - Ranchman's Tiger Moth - Hodges#8163" (On-line). BugGuide. Accessed October 05, 2021 at https://bugguide.net/node/view/25622.

Grof-Tisza, P., Z. Steel, R. Karban. 2017. The Spatial Distribution and Oviposition Preference of the Ranchman's Tiger Moth, Platyprepia virginalis (Lepidoptera: Erebidae). The Journal of the Lepidopterists' Society, 71(1): 16-19. Accessed October 05, 2021 at https://doi.org/10.18473/lepi.v71i1.a4.

Karban, R., C. Karban, M. Huntzinger, I. Pearse, G. Crutsinger. 2010. Diet mixing enhances the performance of a generalist caterpillar, Platyprepia virginalis. Ecological Entomology, 35: 92-99.

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