Gynaephora groenlandica

Arctic woolly bear moth
Arctic woolly bear caterpillar, Baffin Island
Scientific classification
Kingdom:Animalia
Clade:Euarthropoda
Class:Insecta
Order:Lepidoptera
Superfamily:Noctuoidea
Family:Erebidae
Genus:Gynaephora
Species: G. groenlandica
Binomial name
Gynaephora groenlandica
(Wocke, 1874)
Synonyms
  • Dasychira groenlandica Woke, 1874[1]

Gynaephora groenlandica, the arctic woolly bear moth, is an erebid moth endemic to the high Arctic, specifically the Canadian archipelago and Greenland.[2] It is best known for its slow rate of development, as its full caterpillar life cycle may extend up to 15 years, and 4 years may elapse between molts. This species remains in a larval state for the vast majority of its life.[2][3] Unique among Lepidoptera, it undergoes an annual period of diapause that lasts for much of the calendar year, as G. groenlandica is subject to some of the longest, most extreme winters on Earth.[4][5] In this dormant state, it can withstand temperatures as low as −70 °C.[4]

This species has an alpine subspecies which is notable for its geographic distribution south of the High Arctic. Females generally do not fly, while males are much more active in this capacity.[4][6] The arctic woolly bear moth also exhibits the behavior of basking, which aids in temperature regulation and digestion and affects both metabolism and oxygen consumption.[2][3] G. groenlandica may also represent a useful indicator species for the effects of global warming in the High Arctic due to temperature-based feeding tendencies.[7]

Description

In general, G. groenlandica larvae are large (~300 mg) and coated in soft hair.[7][8] While they have a distinctive tan-brown cast, their color may vary.[7] They are characterized by a distinct hair tuft, which has been referred to as a "rudimentary hair pencil", on their eighth abdominal segment .[4][7] Later larval instars are notable for the color pattern of this dorsal hair tuft. They can also be identified by the form of their hairs, which are spineless, in contrast to the finer, feather-like hairs of their close relative, G. rossii.[7] They may also be distinguished from G. rossii in terms of wing pattern: G. groenlandica lack the broad, dark band along the edge of their hind wings that is characteristic of G. rossii. In general, G. rossii also have more wing patterning than G. groenlandica.[7]

Geographic range

The arctic woolly bear moth is endemic to the Canadian Arctic Archipelago and Greenland, or above approximately 70°N latitude. It is therefore officially classified as a High Arctic endemic species[2][7] It is known as one of the most northern members of the Lepidopteran order in the Northern hemisphere.[4] Data published in December 2013 presented the first records of G. groenlandica south of the Arctic Circle. Specifically, they were found in the alpine environment of the southwest Yukon, 900 kilometers south of their previously defined range. These populations were subsequently categorized as the subspecies G.g. beringiana.[7]

This species is also noteworthy for its presence on Ellesmere Island. This was highlighted in BBC's sequel to Planet Earth, called Frozen Planet, which was broadcast on BBC One in autumn 2011 (with the US broadcast following on Discovery Channel in spring 2012).[6]

Habitat

G. groenlandica is well-adapted to living in conditions of extreme cold in the High Arctic.[4]

At two distinct field sites on Ellesmere Island, it was discovered that G. groenlandica, when in a diapausal state, tend to exist in specific micro-habitats rather than in a random geographic distribution. Hibernacula are frequently found secured to the base of rocks, as opposed to being attached to vegetation. At one investigation site, hibernacula were observed primarily on the lee-ward side of rocks (that is to say, on the side sheltered from the wind), suggesting that wind direction plays a role in the selection of hibernation sites.[7][5]

In captivity, G. groenlandica have also been observed anchoring themselves to leaf litter of Salix arctica during this diapausal period.[5]

Home range and territoriality

The G. groenlandica caterpillar moves up to several meters per day, primarily in order to acquire necessary resources.[9] In comparing a group of caterpillars physically transferred between Salix arctica (arctic willow) plants and a second group in which each individual was restricted to a single willow for the duration of the larval active period, it was observed that transferred larvae demonstrated higher herbivory and growth rates compared to the stationary group. This implies that the acquisition of high quality resources may be a primary reason for the movement of G. groenlandica larvae between host plants.[9]

Food resources

Host plant preferences and selection

Salix arctica, the arctic willow, is the larva's primary host plant.

As G. groenlandica spends much of its life in a larval state, food resources are relevant to its larval stage of development. Salix arctica, the arctic willow, is the primary host plant and food source for this species.[9][3] G. groenlandica larvae may also feed on plants of other families, such as the flowers of Saxifraga oppositifolia and the senescent leaves of Dryas integrifolia. Less than 3% of larvae, however, have been found to choose these alternatives.[2]

Compared to High Arctic populations, in lower and warmer sites in Canada, G. groenlandica larvae eat less S. arctica. For comparison, the G. g. beringiana subspecies found in the alpine environments of southwest Yukon feed on a broader spectrum of plants than more northern populations.[7][10][11] The highest levels of herbivory for this species have been discovered at sites of intermediate temperature for its range in Canada. This can be attributed to the narrow thermal adaptation of this species, implying that it cannot increase its levels of herbivory at warmer sites within its geographical distribution.[11]

While larvae rarely eat the catkins (petal-less flower clusters) of S. arctica,they readily consume the plant's leaves. 97% of larvae which actively eat at the onset of their feeding season are consuming the new leaf buds of this plant. It has also been shown, by comparing the nutrient concentrations of plant leaves compared to those of larval frass, that larvae remove both nitrogen and potassium from the plant when feeding.[9] Through further examination, it has been noted that larvae only feed in June, which is when the leaves of S. arctica reach their peak concentrations of nutrients and total non-structural carbohydrates. The caterpillars decrease their food intake towards the end of the month and into the summer. At this time, the levels of total non-structural carbohydrates and nutrients in S. arctica leaves tend to decrease, and concentrations of phenols and tannins increase.[2][3][12] This decrease in nutrients and carbohydrates, combined with an increase in secondary metabolites, may account for this decline in consumption.[12]

Life history

The life history traits of G. groenlandica are dictated by the short, cold nature of summers in the High Arctic.[10] Due to its restricted seasonal growth period, G. groenlandica has a life cycle of approximately 10 years. That being said, its lifespan has been known to extend to at least 14 years at the Alexandra Fiord lowland and at Ellesmere Island.[2][3][7] In contrast, its lifespan is much shorter (2–3 years) in warmer, alpine environments.[7] Arctic woolly bear moths remain larvae for the vast majority of their lives, with the exception of up to 3–4 weeks of a single summer.[3] This extended developmental period is not only attributed to low environmental temperatures, but also to the nutrition provided by its host plants .[7] While they remain in their extended larval stage, G. groenlandica experience annual winter diapauses that commence in late June or early July.[4][5] Larval mortality in an experimental caged environment on the tundra was found to be 10%.[13]

Life cycle

This species spends the vast majority of its life as a late larval instar; its early larval and adult stages represent only 6% of its full life cycle. It is the later instars which experience multiple annual periods of diapause.[12] During this dominant stage of their lives (from the third to sixth instar phases), G. greenlandica only molt every 3–4 years.[12]

Larval activity is confined to a short period following snowmelt. The High Arctic presents a short growing season of 45–70 days, and the G. groenlandica cease foraging at the end of June, prior to mid-summer.[2] Larvae tend to spend 95% of their time either basking in the sun, feeding, or moving, and only 5% of their time fully immobile. More specifically, about 60% of their time as larvae is spent basking, 20% is spent feeding, and 15% is spent moving.[12]

In late June or early July, the larvae prepare to overwinter by weaving silken hibernacula and entering diapause until the subsequent snowmelt.[4][5][7] This typically occurs when daytime temperatures are at a maximum of 5-10 °C. In their diapausal state, G. groenlandica can withstand temperatures as low as -70 °C, and winter mortality is limited to, on average, a maximum of 13% of the population.[4][12][14]

The developmental stages of pupation, emergence, mating, egg laying, eclosion, and molting to the second instar stage are all confined to a period of 3–4 weeks during a single summer. Emergence and reproduction may occur in a 24-hour period.[2][7]

Because the lifespan of fully mature adult individuals is very brief, adult moths of this species are difficult to find in the wild.[7]

Enemies

Predators

G. groenlandica has a distinct defense reaction to bat signals.[4] Some species of Arctic moths show evidence of degradation of defensive reactions to bats, presumably due to spatial isolation from this predator. G. groenlandica, however, continues to possess this defensive behavior. When arctic woolly bear moths are exposed to bat-like ultrasound (26 kHz and 110 dB sound pressure level root mean square at 1m), males respond by reversing their flight course. Responses to the sound have been observed from up to 15-25m away. Females, however, have a degenerating bat-sensing system. There are two presumed reasons for this. Firstly, females tend to be flightless and thus do not require this adaptation. Secondly, an auditory system would compete for space with the ovaries, and the cost of this defense mechanism may outweigh the benefit of having fully functional reproductive organs.[15]

Parasitoids

The primary enemies, and primary mortality factor, of G. groenlandica caterpillars are parasitoids, namely Exorista thula and the ichneumonid wasp Hyposoter diechmanni.[9][13][16] In general, more than two thirds of Gynaephora are killed by parasitoids, and parasitism in G. groenlandica causes more than 50% mortality.[3][11] The probability of parasitism increases towards the end of the species’ active period, which coincides with declining rates of feeding.[4]

The tachinid fly Exorista thula also poses a threat to G. groenlandica. A solitary parasitoid, it kills roughly 20% of the third and fourth instars of its host.[17]

The hibernaculum, in which larvae spend a dominant portion of their lives, acts as a defensive barrier to parasitism.[13]

Genetics

Subspecies and hybridization

While G. groenlandica is generally classified as a High Arctic endemic species, an article published in December 2013 contained the first reports of G. groenlandica in alpine environments. Specifically, two neighboring populations were discovered in the southwest Yukon, 900 kilometers south of their previously defined southern distributive border. Due to the distinct habitat, geography, DNA barcode haplotype, and wing phenotype of these two populations, they were classified as the subspecies G.g.beringiana.[7]

While G. groenlandica is a close relative of G. rossii, the two species are reproductively isolated and no hybridization occurs.[7]

Physiology

Flight

While females of this species have fully developed wings and may take flight for a short time, they usually do not fly. It is worth noting, however, that while Arctic-inhabiting females tend to remain flightless, females of the more southern alpine subspecies are often more mobile.[4][7]

In contrast, males tend to fly high, fast, and erratically during the day.[7]

Thermoregulation

The period of maximal activity for G. groenlandica is in June, during the annual period of maximal solar radiation (24 hours of sunlight) in the High Arctic; however, temperatures at this time continue to be extremely low. Ground temperatures in June, for instance, are usually less than 10 °C.[3][12] At this time, the body temperatures of feeding larvae tend to be similar to those of molting and spinning larvae, while those of “basking” larvae tend to be higher.[3] G. groenlandica larvae spend approximately 60% of their time basking, including during periods of pupation.[12] The behavior of basking is characterized as the action of a caterpillar orienting its body so as to maximize sun exposure and avoid wind. Larvae tend to follow the direct angle of the sun’s rays in order to maintain maximal absorption of sunlight. They do this by orienting perpendicularly to the sun’s angle of insolation.[3] Through the act of basking, G. groenlandica larvae may raise their body temperature by up to 20 °C. Generally, maximal body temperature is approximately 30 °C.[2][4][3] This peak temperature is generally only reached when larvae lie in midday sun, surrounded by snow, on a day with minimal wind.[3]

Solar radiation promotes larval growth, and thus basking may increase developmental rates.[2][3] When comparing larval growth rates at 5, 10, and 30 °C, respectively, growth and metabolic rates were found to be lowest at 5 °C and maximized at 30 °C.[2] This trend exhibits a specific relationship: as body temperature increases due to basking, metabolic rates increase exponentially. This was found to hold true even when larvae were starved or seemingly inactive.[2][3]

In general, feeding larvae tend to have lower body temperatures than basking larvae. Therefore, larvae tend to feed when temperatures are highest, and they bask when they cannot reach the higher temperatures (more than 5 -10 °C) needed for activity.[2] It has been suggested that without the help of basking in 24-hour sunlight during High Arctic summers, larvae would rarely exceed their developmental threshold of ~5 °C.[12] This may account for the unique tendency of the arctic woolly bear moth to have short feeding periods during times of peak insolation, followed by lengthier periods of basking and digestion.[12]

In early to mid-June, larval metabolism tends to be greatly impacted by food intake and rising temperature. Later in the active season, they become much more metabolically insensitive to temperature, and energy obtained via food consumption is conserved.[18]

Changes in metabolic state and body temperature also affect oxygen consumption.[2][3] Oxygen consumption was found to be much lower when larval body temperatures were below 10 °C.[3] Low oxygen consumption was also observed in inactive larvae. In contrast, it was found to be higher for caterpillars that were moving or starved, higher still for digesting larvae, and highest for feeding larvae.[2]

Digestion

Larvae frequently bask for roughly 5 hours after feeding before moving to a new site.[2][3] A consequent increase in body temperature stimulates gut enzyme activity, promoting a higher digestion rate.[3] G. groenlandica’s level of efficiency for the conversion of ingested food exceeds the mean value of efficiency of other Lepidopteran species.[2]

Diapause

G. groenlandica experiences a period of winter diapause during which it remains dormant within a hibernaculum. In this state, it can withstand temperatures as low as -70 °C.[4] Encasing itself within a hibernaculum during diapause serves several functions: protection from parasitoids, avoidance of diminished nutrient concentration in their primary food source, Salix arctica, degradation of mitochondria linked to hypometabolism and antifreeze synthesis, and general conservation of energy reserves.[3][4][17]

These cocoons are made of silk and consist of two layers, into which larval hairs are incorporated.[7][14] In a 1995 study of experimentally caged larvae in the Canadian High Arctic Archipelago, 81% of larvae spun hibernacula.[13]

During the active season, larvae orient towards solar radiation, and each spins their respective hibernaculum over a 24-hour period.[4][5] They generally pupate with their head facing south, in a north-south orientation.[3] This cocoon helps the larvae to accumulate heat more effectively.[4]

G. groenlandica often anchor their hibernacula to the base of rocks. In captivity, G. groenlandica have also been observed to attach themselves to Salix arctica leaf litter during the diapausal period.[5] In the 1995 study mentioned above, in which larvae were kept in a cage-controlled environment on the High Arctic tundra, more hibernacula were actually observed on the predominant plant cover of Dryas integrifolia (mountain avens) and Cassiope tetragona (Arctic white heather) as opposed to on their principal host plant, S. arctica.[13] Almost half of the larvae which spun hibernacula did so in conjunction with other larvae, forming joint cocoons. Upwards of three caterpillars were occasionally observed sharing a common hibernaculum, but the most common case was that of two individuals sharing a joint cocoon. Higher rates of communal hibernacula occurred at lower population densities per cage.[13]

As temperatures decrease in the late Arctic summer, larvae begin synthesizing cryoprotective compounds, such as glycerol and betaine. Accumulation of these "antifreezes" (which protect cells from cold conditions) is aided by the bottlenecking of oxidative phosphorylation through mitochondrial degradation. While the larvae continue to produce energy from stored glycogen in their frozen state, this mitochondrial degradation causes their metabolism to drop so low as to almost stop entirely, inducing dormancy. Mitochondrial functioning may be fully restored in the spring after mere hours of resumed larval activity.[4][19]

Conservation

Warming temperatures and herbivory

At warmer temperatures, arctic moth larvae generally tend to have higher respiration rates and lower growth rates. They also tend to shift their diets to more nutrient-rich foods in this type of environment. For instance, the herbivory rate of the main food source for G. groenlandica, S. arctica, is altered at elevated temperatures.[7] This implies environmentally dependent host plant plasticity in G. groenlandica. It also suggests that an increase in temperature due to global warming may have significant effects on the behavior of northern herbivore invertebrates such as G. groenlandica, as well as effects on the herbivory rates of their food sources. Thus, G. groenlandica may represent a potential indicator species for future studies on climate change.[4][10][7]

See also

References

  1. ↑ von Homeyer, Alexander (1874). "Lepidopteren". Wissenschaftliche Ergebnisse. Die zweite Deutsche Nordpolarfahrt. 2. Leipzig: F. A. Brockhaus. pp. 409–410.
  2. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Kukal, Olga; Dawson, Todd E. (1989-06-01). "Temperature and food quality influences feeding behavior, assimilation efficiency and growth rate of arctic woolly-bear caterpillars". Oecologia. 79 (4): 526–532. Bibcode:1989Oecol..79..526K. doi:10.1007/BF00378671.
  3. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Kukal, Olga (March 24, 1988). "Behavioral Thermoregulation in the Freeze-Tolerant Arctic Caterpillar, Gynaephora groenlandica" (PDF). The Company of Biologists Limited.
  4. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Makarova, O. L.; Sviridov, A. V.; Klepikov, M. A. (2013-04-01). "Lepidoptera (Insecta) of polar deserts". Entomological Review. 93 (2): 225–239. doi:10.1134/S0013873813020115.
  5. 1 2 3 4 5 6 7 Bennett VA, Lee RE Jr, Nauman JS, Kukal O. Selection of overwintering microhabitats used by the arctic woollybear caterpillar, Gynaephora groenlandica. Cryo Letters. 2003 May-Jun;24(3):191-200.
  6. 1 2 Levin, Gary (April 8, 2008). "Another sweeping nature special when 'Planet' freezes over". USA Today. Retrieved May 25, 2010.
  7. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Barrio, Isabel C.; Schmidt, B. Christian; Cannings, Sydney; Hik, David S (December 2013). "Fist Records of the Arctic Moth Gynaephora groenlandica (Wocke) South of the Arctic". Arctic. 66: 429–434. doi:10.14430/arctic4329.
  8. ↑ Barrio IC, Hik DS, Peck K, Bueno CG. 2013 After the frass: foraging pikas select patches previously grazed by caterpillars. Biol Lett 9: 20130090. https://dx.doi.org/10.1098/rsbl.2013.0090
  9. 1 2 3 4 5 Greyson-Gaito, Christopher J.; Barbour, Matthew A.; Rodriguez-Cabal, Mariano A.; Crutsinger, Gregory M.; Henry, Gregory H. R. (April 2016). "Freedom to move: Arctic caterpillar (Lepidoptera) growth rate increases with access to new willows (Salicaceae)". The Canadian Entomologist. 148 (6): 673–682. doi:10.4039/tce.2016.22.
  10. 1 2 3 Barrio, I. C.; Hik, D. S.; Liu, J. Y. (May 2014). "Diet breadth of Gynaephora groenlandica (Lepidoptera: Erebidae): is polyphagy greater in alpine versus Arctic populations?". The Canadian Entomologist. 147 (2): 215–221. doi:10.4039/tce.2014.35.
  11. 1 2 3 Birkemoe, Tone; Bergmann, Saskia; Hasle, Toril E.; Klanderud, Kari (2016-10-01). "Experimental warming increases herbivory by leaf-chewing insects in an alpine plant community". Ecology and Evolution. 6 (19): 6955–6962. doi:10.1002/ece3.2398.
  12. 1 2 3 4 5 6 7 8 9 10 Lee, Richard (2012-12-06). Insects at Low Temperature. Springer Science & Business Media. ISBN 9781475701906.
  13. 1 2 3 4 5 6 Kukal, Olga (1995-04-01). "Winter mortality and the function of larval hibernacula during the 14-year life cycle of an arctic moth, Gynaephora groenlandica". Canadian Journal of Zoology. 73 (4): 657–662. doi:10.1139/z95-077.
  14. 1 2 Laity, Peter R.; Holland, Chris (2017-02-01). "Thermo-rheological behaviour of native silk feedstocks". European Polymer Journal. 87 (Supplement C): 519–534. doi:10.1016/j.eurpolymj.2016.10.054.
  15. ↑ Rydell, J., et al. “Persistence of Bat Defence Reactions in High Arctic Moths (Lepidoptera).” Proceedings of the Royal Society B: Biological Sciences, vol. 267, no. 1443, 2000, pp. 553–557., doi:10.1098/rspb.2000.1036.
  16. ↑ Varkonyi, Gergely; Tomas Roslin (2013). "Freezing cold yet diverse: dissecting a high-Arctic parasitoid community associated with Lepidoptera hosts". Canadian Entomologist. 145: 193–218. doi:10.4039/tce.2013.9.
  17. 1 2 Morewood, W. Dean; D. Monty Wood (2002). "Host utilization by Exorista thula Wood (sp. nov.) and Chetogena gelida (Coquillett) (Diptera: Tachinidae), parasitoids of arctic Gynaephora species (Lepidoptera: Lymantriidae)". Polar Biology. 25: 575–582. doi:10.1007/s00300-002-0382-y.
  18. ↑ Hodkinson, Ian D. (2005). "Adaptations of invertebrates to terrestrial Arctic environments" (PDF). Transactions of the Royal Norwegian Society of Sciences and Letters: 28–29 – via ResearchGate.
  19. ↑ Hoffmann, Klaus H. (2014-12-19). Insect Molecular Biology and Ecology. CRC Press. ISBN 9781482231892.

Further reading

  • Heinrich, Bernd (1993). The hot-blooded insects: strategies and mechanisms of thermoregulation. Harvard University Press.
  • Chapman, R. F. (1998). The insects: structure and function. Cambridge University Press. ISBN 978-0-521-57890-5.
  • Kukal, O.; Kevan, P.G. (1987). "The influence of parasitism on the life history of a high arctic insect, Gynaephora groenlandica (Wöcke) (Lepidoptera: Lymantriidae)". Can. J. Zool. 65: 156–163. doi:10.1139/z87-022.
  • Kukal, O (1988). "Caterpillars on ice". Natural History. 97: 36–41.
  • Kukal, O.; Duman, J.G.; Serianni, A.S. (1988). "Glycerol metabolism in a freeze-tolerant arctic insect: An in vivo 13-C NMR study". J. Comp. Physiol. B. 158: 175–183. doi:10.1007/bf01075831.
  • Kukal, O.; Heinrich, B.; Duman, J.G. (1988). "Behavioural thermoregulation in the freeze-tolerant arctic caterpillar, Gynaephora groenlandica". J. Exp. Biol. 138: 181–193.
  • Kukal, O.; Dawson, T.E. (1989). "Temperature and food quality influences feeding behavior, assimilation efficiency and growth rate of arctic woolly-bear caterpillars". Oecologia. 79: 526–532. Bibcode:1989Oecol..79..526K. doi:10.1007/bf00378671.
  • Kukal, O.; Duman, J.G.; Serianni, A.S. (1989). "Cold-induced mitochondrial degradation and cryoprotectant synthesis in freeze-tolerant arctic caterpillars". J. Comp. Physiol. B. 158: 661–671. doi:10.1007/bf00693004.
  • Kukal, O. 1990. Energy budget for activity of a high arctic insect, Gynaephora groenlandica (Wöcke) (Lepidoptera: Lymantriidae). In: C.R. Harington (ed) Canadian Arctic Islands: Canada's Missing Dimension. National Museum of Natural History, Ottawa, Canada.
  • Kukal, O. 1991. Behavioral and physiological adaptations to cold in a freeze-tolerant arctic insect. In: R.E. Lee and D.L. Denlinger (eds) Insects at Low Temperature. Chapman and Hall, N.Y.
  • Kukal, O. 1993. Biotic and abiotic constraints on foraging of arctic caterpillars. In: N.E. Stamp and T.M. Casey (eds) Caterpillars: Ecological and Evolutionary Constraints on Foraging. Chapman and Hall, N.Y.
  • Kevan, P.G.; Kukal, O. (1993). "A balanced life table for Gynaephora groenlandica (Lepidoptera: Lymantriidae) a long-lived high arctic insect, and implications for the stability of its populations". Can. J. Zool. 65: 156–163.
  • Danks, H.V.; Kukal, O.; Ring, R.A. (1994). "Insect cold-hardiness: Insights from the arctic". Arctic. 47 (4): 391–404. doi:10.14430/arctic1312.
  • Kukal, O (1995). "Winter mortality and the function of larval hibernacula during the 14-year life cycle of an arctic moth, Gynaephora groenlandica". Can. J. Zool. 73: 657–662. doi:10.1139/z95-077.
  • Bennett, V. A; Kukal, O.; Lee, R.E. (1999). "Metabolic opportunists: Feeding and temperature influence the rate and pattern of respiration in the high arctic woollybear caterpillar, Gynaephora groenlandica (Lymantriidae)". J. Exp. Biol. 202: 47–53.
  • Bennett, V.A.; Lee, R. E. Jr.; Nauman, J.S.; Kukal, O. (2003). "Selection of overwintering microhabitats used by the arctic woollybear caterpillar, Gynaephora groenlandica". CryoLetters. 24 (3): 191–200.
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