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Leptarctia californiae

By Claire Walther and Galen Burrell

Geographic Range

California tiger moths (Leptarctia californiae) are native to the Nearctic region. They are mainly present in the western half of the United States, throughout the Intermountain West and along the Pacific Coast. There are also populations in western parts of northern Mexico and southern parts of British Columbia, Canada. Presently, California tiger moths seem to occupy an area similar to their historical range, but populations are dispersed and are less common compared to historic records. (Crabo and Hammond, 2021)

Habitat

California tiger moths primarily inhabit forests and are most active in open areas, such as open-canopy woodlands, clear-cuts, or meadows. They are typically found in montane areas at intermediate elevations and are uncommon in arid regions, although they occupy coastal dunes along the Pacific Coast. The exact range of elevations that California tiger moths occupy is unknown. (Crabo and Hammond, 2021)

Physical Description

California tiger moth adults are small or intermediate in size, with forewings measuring between 26 and 34 mm. California tiger moths are highly polymorphic, with a wide range of morphological variation between populations. This makes it difficult to identify them consistently by appearance alone. Their forewings vary in color, but are typically dark gray or black with white spots, faint white stripes, or white marbling. The hindwings of California tiger moths are usually bright orange or red, but can range from white to almost entirely black. Their hindwings also have black stripes or splotches along the posterior edges, but there is still a great deal of intraspecific variation. For example, populations with darker hindwings tend to have white, yellow, or orange markings. The ventral sides of their wings are often much brighter, and can be almost entirely orange or red, matching the dorsal sides of their hindwings. California tiger moths usually have dark bodies, but can have white or cream-colored hairs along their margins and near their heads. Although there is very little sexual dimorphism, males have more pronounced pectinate antennae compared to females.

California tiger moth larvae are small, reaching 1.5 to 2 cm in length. They are initially light colored with rows of black tubercles along their dorsal and lateral sides. From each tubercle sprouts a cluster of long urticating hairs, which protect larvae from predators. As larvae progress into later instars, their heads develop a reddish-brown color and their bodies become dark gray with faint orange ventral spots and a faint orange dorsal line. Their urticating hairs also become darker, and the hairs on their posterior ends grow longer than those on the rest of their bodies. California tiger moth larvae use a combination of silk and their own hairs to create a cocoon, in which they pupate before emerging as adults. Pupae are dark brown and approximately 1 cm in length. (French, 1889; "Species Leptarctia californiae - Hodges#8126", 2021; McLeod, 2019)

  • Sexual Dimorphism
  • sexes alike
  • Range wingspan
    26 to 34 mm
    1.02 to 1.34 in

Development

There is relatively limited information regarding the development of California tiger moths specifically. Females lay eggs on vegetation beginning in March and April and larvae eclose anywhere from 4 to 21 days after eggs are laid. Larvae develop through five instar stages, growing in size and darkening in color with each instar. Larvae spend about 4 to 7 days in each of the first four instars, typically reaching the fifth instar by early to mid-July. Larvae spend 40 to 60 days in their fifth instar, although French (1899) observed that they reach full size within a few days and are inactive for the majority of this period. Fifth instar larvae build cocoons and pupate beginning around August and September. Pupae enter diapause and overwinter for 6 to 7 months in leaf litter, emerging as adults in early to mid-spring.

It should be noted that the timing of various developmental stages may be impacted by local climates, especially given the large range of latitudes that California tiger moth occupy. Other wide-ranging tiger moths (subfamily Arctiinae) in North America have one brood per year (univoltine) at higher latitudes and two or more broods (multivoltine) at lower latitudes. Furthermore, the timing of larval activity and pupation for populations in arid regions often coincides with rainy and dry periods, respectively. (Conner, 2008; French, 1889; Mays, 1966)

Reproduction

There is limited information regarding the mating behavior of California tiger moths specifically. Males show an attraction to pheromones released by unmated females, but do not show the same attraction to females that have already mated. It is therefore likely that California tiger moths are polygynous, but this has not been confirmed. (Mays, 1966)

There is limited information regarding the mating behavior of California tiger moths specifically. Adult activity typically begins in the beginning or middle of spring, although at higher altitudes they may be active into summer. They are most active during the warmest parts of the day and in sunny conditions. Females fly infrequently and often only short distances, spending most of their time resting on vegetation or leaf litter. Conversely, males fly regularly and erratically in open areas or along forest edges. Males likely locate females using a combination of chemical and visual stimuli. Females sit on low-lying vegetation and release pheromones that attract mates. Copulation lasts between 2 and 5 hours, after which mating pairs separate and females seek oviposition sites.

Females begin depositing eggs within a day of mating, laying clusters of 10 to 40 eggs on low vegetation, such as the undersides of leaves. Females lay between 200 and 400 eggs in total, often within a week of copulation. Eggs are about 0.75 mm in diameter, round, and pearly white. Under laboratory conditions, eggs may hatch in a matter of 4 to 7 days, whereas observations under field conditions demonstrate that eggs may take up to 21 days to hatch. Larvae are immediately independent at birth and typically pupate beginning in August or September. Adults eclose from pupae the following spring. (French, 1889; Mays, 1966)

  • Breeding interval
    California tiger moths breed once yearly.
  • Breeding season
    California tiger moths breed from early March to early May.
  • Range eggs per season
    200 to 400
  • Range gestation period
    1 to 7 days

California tiger moths exhibit no parental investment beyond the act of mating. Females select oviposition sites on low-lying vegetation, often on the undersides of leaves, which may provide some protection from predators. Larvae are independent upon hatching. Immediately after hatching, larvae eat some or all of their egg cases, which thus serve as an important first meal. (Conner, 2008; Mays, 1966)

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

There is limited information regarding the maximum lifespan of California tiger moths. Larvae hatch from eggs in mid-spring and complete metamorphosis early the following spring. Adult moths are estimated to live 2 to 3 weeks at most, meaning California tiger moths likely complete their life cycle in about one year. (Mays, 1966)

Behavior

Adult California tiger moths are diurnal and motile. They are often found in open areas near woodlands, either walking on low-lying vegetation or flying just above it. Adults are mostly active in spring and early summer, often during the warmest parts of the day (i.e., early afternoon) and especially in sunny weather. Adults become active sooner at lower elevations or in warmer climates. Indeed, emergence dates have occurred earlier in recent years, likely due to elevated spring temperatures as a result of climate change. At higher altitudes, where conditions are cooler, adult emergence occurs later and activity continues into July or early August. California tiger moths are becoming more common at higher altitudes as the climate continues to warm.

California tiger moth larvae spend most of their time feeding on foliage of various plant species. Early instars exhibit both diurnal and nocturnal feeding activity, whereas later instars preferentially feed nocturnally. Early instar larvae often feed on the undersides of leaves, which likely reduces the chances of detection by predators. When larvae are not actively feeding, or if they are disturbed, they descend to ground level and hide in leaf litter.

California tiger moths pupate in late summer or early fall, as daily temperatures decrease. Larvae seek shelter in ground litter and pupate inside of cocoons made of silk and urticating hairs. California tiger moths overwinter as pupae in a state of diapause. Adults emerge as temperatures warm again in spring. (French, 1889; Maurer, et al., 2018; Mays, 1966)

Home Range

There is limited information regarding the home range of California tiger moths. Larvae disperse seemingly randomly from where they hatch. However, research on Ranchman's tiger moths (Arctia virginialis), another day-flying species, suggests that larvae do not disperse far from the areas where they hatch. Ranchman's tiger moth adults exhibit hilltopping behavior, dispersing towards local high points to improve their chances of locating mates. After mating, they do not always return to their own natal areas, sometimes moving over 500 m before selecting oviposition sites.

It is unclear whether California tiger moths exhibit the same dispersal patterns as Ranchman's tiger moths. However, given the similarities in life history between the two species, it is possible that their dispersal patterns are also similar. California tiger moths do not appear to defend territories, either as larvae or as adults. (Mays, 1966; Pepi, et al., 2022)

Communication and Perception

There is limited information regarding communication and perception in California tiger moths specifically. Caterpillars likely rely on chemical stimuli to locate suitable food sources, but may also use visual and tactile cues to respond to predation threats. Adults also rely primarily on chemical and visual stimuli to find mates. Females sit conspicuously on vegetation in open areas and release pheromones to attract males. Tactile stimuli are important during copulation, as mating pairs must align their genitalia to successfully fertilize eggs. Adults may also use visual stimuli to avoid diurnal predators.

Tiger moths (subfamily Arctiinae) have tympana capable of detecting acoustic stimuli produced by echolocating bats. Many species also have tymbals, which produce sounds that disrupt the accuracy of bat echolocation. In most diurnal species these tympana and tymbals are greatly reduced in size and function. However, some diurnal species still respond to certain acoustic stimuli with evasive behaviors or produce sounds using their tymbals. It is unclear whether California tiger moths have retained functionality in these organs, but it is possible that they are still capable of communicating or perceiving their environment with acoustic stimuli. (Conner, 2008; Mays, 1966)

Food Habits

California tiger moth larvae are considered generalist herbivores. Common host plant genera likely include brackenfern (genus Pteridium), mallows (genus Malva), brambles (genus Rubus), currants (genus Ribes), beardtongues (genus Penstemon), plums (genus Prunus), oaks (genus Quercus), and willows (genus Salix).

It is unclear whether California tiger moths feed as adults. There is little information regarding their mouthpart morphology and there are no known observations of California tiger moths visiting flowers for nectar. ("California Tiger Moth", 2021; Mays, 1966)

  • Plant Foods
  • leaves
  • flowers

Predation

There is limited information regarding specific predators of California tiger moths. Larval predators include the larvae of green lacewings (family Chrysopidae) and adult Audouin's night-stalking tiger beetles (Omus audouini). California tiger moths have also been found in the stomach contents of Trowbridge's shrews (Sorex trowbridgii) and are probably eaten by other small mammals. Additional predators likely include other arthropods as well as amphibians, reptiles, and insectivorous birds.

California tiger moth adults vary widely in color between populations, but most morphs have bright orange, yellow, or red markings on their wings. The rest of their wings and bodies are dark in color and often have disruptive coloration. The combination of crypsis and aposematism protects adult California tiger moths from many predators.

California tiger moth larvae are covered in long urticating hairs, which are irritating when touched and provide protection from predators. Larvae also exhibit behaviors that help them avoid predation. Early instar larvae frequently feed on the undersides of leaves, possibly to avoid detection from above. Furthermore, larvae reduce their daytime activity as they grow larger and more visible to diurnal predators. When disturbed, larvae curl into balls and drop from vegetation into ground litter below. They often seek shelter among leaf litter when threatened or not actively foraging. If larvae are threatened and cannot escape, they raise their posterior ends, where their urticating hairs are longest, and thrust them towards the disturbance. Larvae also excrete feces and liquid matter when threatened, a defense mechanism that is common among larvae of many butterflies and moths (order Lepidoptera).

As larvae, some species of tiger moths (subfamily Arctiinae) are able to process toxic chemicals from host plants and incorporate them into their bodies, which can make them distasteful or toxic when consumed. These toxins can also be maintained through metamorphosis and expressed in adults and their eggs, providing further defense against predators. However, it is unclear whether California tiger moths express toxins obtained from their diet. (Conner, 2008; Mays, 1966; Yates, 2020)

Ecosystem Roles

There is little information regarding the ecosystem roles that California tiger moths serve. As generalist herbivores, they may impact the health of various herbaceous plant species. However, both larvae and adults may serve as an important food source for arthropods, small mammals, reptiles, amphibians, and birds. Under beneficial environmental conditions, some species of tiger moths (subfamily Arctiinae) can reach high levels of local abundance. Under such outbreak conditions, the effects that tiger moths have on the surrounding ecosystem can be intensified.

There are no known accounts of mutualisms in which California tiger moths are involved. The only reports of parasitism involved microsporidians present in laboratory conditions. California tiger moths are also hosts for parasitoid ichneumon wasps (family Ichneumonidae). (Conner, 2008; Mays, 1966; Yates, 2020)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

California tiger moths provide no clear economic benefits, although the roles they play in maintaining functioning ecosystems are not fully understood. More research is needed to determine the impacts, both direct and indirect, that California tiger moths have on human populations.

Economic Importance for Humans: Negative

California tiger moths have no known negative economic impacts. Because they are generalist herbivores, they may defoliate crop plants such as currants (genus Ribes), plums (genus Prunus), and bramble berries (genus Rubus). However, their impact on the agricultural industry has not been evaluated and may be insignificant. More research is needed to determine the impacts, both direct and indirect, that California tiger moths have on human populations. ("California Tiger Moth", 2021)

Conservation Status

California tiger moths have no special status on the IUCN Red List, in the CITES appendices, or on other national or international conservation lists. They are considered to have stable populations throughout their geographic range.

Other Comments

Much of the information presented in this account is based on a few landmark studies on California tiger moths at field sites in Oregon or in lab conditions. While the descriptions of morphological variants may represent the species as a whole, it is possible that populations in different geographic regions exhibit physiological or behavioral traits not described by the studies cited.

Contributors

Claire Walther (author), Special Projects, Galen Burrell (author), Special Projects.

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.

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.

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.

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.

internal fertilization

fertilization takes place within the female's body

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.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

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

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

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.

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

tactile

uses touch to communicate

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.

visual

uses sight to communicate

References

Calscape. 2021. "California Tiger Moth" (On-line). California Native Plant Society. Accessed November 15, 2021 at https://calscape.org/lep/Leptarctia-californiae-(California-Tiger-Moth)?srchcr=sc5ee8ba08481da.

Iowa State University Department of Entomology. 2021. "Species Leptarctia californiae - Hodges#8126" (On-line). BugGuide. Accessed November 15, 2021 at https://bugguide.net/node/view/48977.

Conner, W. 2008. Tiger Moths and Woolly Bears: Behavior, Ecology, and Evolution of the Arctiidae. Oxford, UK: Oxford University Press.

Crabo, L., P. Hammond. 2021. "Leptarctia californiae (Walker, 1855)" (On-line). Pacific Northwest Moths. Accessed November 09, 2021 at http://pnwmoths.biol.wwu.edu/browse/family-erebidae/subfamily-arctiinae/tribe-arctiini/leptarctia/leptarctia-californiae/.

French, G. 1889. Preparatory stages of Leptarctia californiae Walker, with notes on the genus. The Canadian Entomologist, 21 (12): 221-226. Accessed May 16, 2023 at https://doi.org/10.4039/Ent21221-12.

Maurer, J., J. Shepard, L. Crabo, P. Hammond, R. Zack, M. Peterson. 2018. Phenological responses of 215 moth species to interannual climate variation in the Pacific Northwest from 1895 through 2013. PLoS one, 13 (9): 1-16. Accessed November 15, 2021 at https://doi.org/10.1371/journal.pone.0202850.

Mays, D. 1966. Biology and adult variability in an Oregon population of Leptarctia californiae (Walker) (Lepidoptera: Arctiidae). Corvallis, OR: Oregon State University. Accessed May 16, 2023 at https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rf55zc263.

McLeod, R. 2019. "Leptarctia californiae" (On-line). BugGuide. Accessed May 12, 2023 at https://bugguide.net/node/view/48977.

Muma, K., J. Fullard. 2004. Persistence and regression of hearing in the exclusively diurnal moths, Trichodezia albovittata (Geometridae) and Lycomorpha pholus (Arctiidae). Ecological Entomology, 29 (6): 718-726. Accessed May 19, 2023 at https://doi.org/10.1111/j.0307-6946.2004.00655.x.

Pepi, A., P. Grof-Tisza, M. Holyoak, R. Karban. 2022. Hilltopping influences spatial dynamics in a patchy population of tiger moths. Proceedings of the Royal Society B, 289: 1-9. Accessed May 19, 2023 at https://doi.org/10.1098/rspb.2022.0505.

Yates, M. 2020. Variation of the Trowbridge’s shrew (Sorex trowbridgii) diet across forest types in the Oregon Cascades. Corvalis, OR: Oregon State University. Accessed May 13, 2023 at https://ir.library.oregonstate.edu/concern/honors_college_theses/7s75dk21k.

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