About Butterflies and Moths – Part 1
By Mary Free, Extension Master Gardener
In North America (north of Mexico), the order Lepidoptera comprises about 12,800 recognized butterfly and moth species, with the latter being most abundant. Butterflies and moths have many things in common. The life cycles of both, during which they undergo complete metamorphosis, include four distinct stages: egg, caterpillar (larva), pupa, and adult (imago). Each species develops at its own pace, so a general time range is applied to each stage described below. The time during which a species may experience a developmental delay during a certain stage is not included in that range (see the section on diapause). Depending on the species, there may be one to multiple generations per season.
Left to right: Luna moth (Actias luna) eggs, caterpillar, male pupa, male adult.
Egg and Caterpillar Stages
Female lepidopterans prefer particular plants for their offspring and use taste sensors on their feet to make sure they choose a suitable host on which to lay their eggs. (See Gardening to Attract Butterflies and Moths and Nectar and Host Plants for Selected Mid-Atlantic Butterflies and Moths posting later this week for a information about and a list of some host plants.) Depending on the species, females may lay each egg singly (like monarchs, Danaus plexippus) or in clusters (like eastern tent caterpillar moths, Malacosoma americanum). Eggs take from about four days to three weeks to develop. Once a caterpillar hatches, it feeds for the next two to six weeks. A caterpillar might increase its body mass 10,000-fold in 2 weeks (Lin et al. 2011), so each time it outgrows its outer protective layer or cuticle, the larva sheds it in a process called molting. It often consumes the shed layer before devouring more plant food. Caterpillars usually molt from four to six times. The larvae between the molts are called instars.
Before it pupates, a butterfly caterpillar positions itself in a particular manner. Brush-footed butterflies (like monarchs) find a support like a twig on which they spin a silk pad. To this they anchor an abdominal hook called a cremaster and hang upside down. Swallowtails and the whites and sulphurs often have both a cremaster and a silk girdle that supports their mid-section. Gossamer-winged butterflies move to the ground or near it and may use a silk girdle. Once positioned, these butterflies molt for a final time revealing the outer shell of the pupa or chrysalis. A moth caterpillar does not produce a chrysalis. Instead, it usually spins a silk cocoon to encase itself before it molts for the last time and forms a pupa, although some moth species pupate underground. During the pupal stage, a caterpillar transforms into a winged adult within a couple of weeks or so.
Adults are vulnerable as they finally emerge from their pupae (the emergence process is called eclosion) as they have to wait for their wings to expand and harden before they can fly away. Unlike caterpillars, whose purpose was to eat and grow, the mission of adults is to mate and reproduce. Mandibles used by caterpillars for chewing leaves, seeds, or other solid foods have been replaced by a long, tubular proboscis used for sipping flower nectar, tree sap, and other liquids, which provide energy. (See Nectar and Host Plants for Selected Mid-Atlantic Butterflies and Moths later this week for a list of some nectar plants.) However, some adults emerge without a mouth, like the luna mouth (Actias luna), which may survive up to a week on stored nutrients. Most adult lepidopterans live only one day to three weeks or so. However, a last generation monarch butterfly that migrates to Mexico to overwinter and then returns to the United States to reproduce in spring can live up to nine months. (See what you can plant to help monarchs later this week)
Left to right: Adult female luna moth (Actias luna) emerging from pupa, expanding wings, about 9.5 hours after emergence.
Many lepidopteran species are genetically predisposed to suspend their development and go into a dormant period or diapause as a normal part of their life cycles. Other species may prolong diapause as a survival mechanism in the face of unfavorable environmental conditions such as extreme temperatures or potential food or rainfall shortages.
It is not unusual for diapause to occur at the egg stage over the winter. For example, a female invasive spongy moth (Lymantria dispar, formerly known as gypsy moth) lays her eggs in early summer on tree trunks or branches near to where she pupated (since she cannot fly). The embryonic larvae develop during the summer. Once mature, they cease development and enter diapause. Insensitive to cold temperatures, they overwinter in the eggs. Once their host plants have leafed out the following spring, they hatch and begin to feast.
Did you know that several moth species have flightless females? Although the female spongy moth has fully formed wings, they cannot lift her heavy body. Phigalia females with drastically reduced wings cannot fly but do some limited crawling. Adult female tussock (Orgyia) and bagworm (Psychidae) moths that are (practically) wingless usually remain in their cocoons or pupation cases. The flying male moths find female mates by the pheromones they exude (Patterson 2007).
Studies show that the arctic wooly bear moth (Gynaephora groenlandica) may have a typical seven-year life cycle with seven instars that experience intermittent diapause during their larval stage (Morewood & Ring 1998). Each instar is active only in June when it molts and alternates between basking to raise its body temperature and foraging/eating. Following this mobile period, it spins a light silk hibernaculum, which it anchors to the base of a rock where it remains for about eleven months, mostly in a frozen state, until the next June. It repeats this cycle each year until it reaches the final instar. Then, “pupation, emergence, mating, egg laying, eclosion and moulting to first and second instar larvae occur in 3–4 weeks in a single summer season” (Kukal & Dawson 1989).
Left to right: Female spongy moth with eggs, arctic wooly bear caterpillar, eastern black swallowtail chrysalis, question mark butterfly, migrating monarchs.
Eastern black swallowtails (Papilio polyxenes) produce two generations in the north and three in the south. The pupal stage for the first brood(s) is two to three weeks. But like other swallowtails, the last generation pupae enter diapause and overwinter as chrysalides as part of their normal life cycle. However, there are lepidopterans that have been known to prolong pupal diapause depending on environmental conditions. In the Mediterranean region, the frequency of extended diapause in the pupae of pine processionary moths (Thaumetopoea) increased in areas where winter temperatures were colder or warmer than normal (Salman et al. 2019). A scarce green-striped white (Euchloe falloui), which inhabits the Negev desert in Israel, reportedly emerged from its pupa after fifteen years (Benyamini 2008). In experiments conducted in Nevada and California, yucca moths (Prodoxus y-inversus) successfully emerged from their pupae after 20, 25, and 30 years in diapause (Powell 2001).
Some adult stage butterflies also experience diapause. Mourning cloak (Nymphalis antiopa), eastern comma (Polygonia comma), and question mark (Polygonia interrogationis) butterflies hibernate in tree hollows, gaps in loose bark or shingles, or wood piles over the winter. Several consecutive warm winter days may beckon out mourning cloaks that have been observed in flight in Massachusetts in every month (French, accessed 2022). A mourning cloak adult can live up to eleven months.
Some monarch adults experience reproductive diapause. A hormone needed for reproduction is (nearly) lacking in the last generation adults that migrate to Mexico. A reproductive adult cannot go into diapause and does not migrate. The migratory monarchs do not become sexually active until mid-February when they are about to begin their travels back north.
Note: Click on images to see enlarged photos, captions, and photo attributions.
On a mobile phone, click on the information symbol (circle with a letter ℹ︎ symbol).
- All About Butterflies. Department of Horticulture. University of Kentucky. (accessed March 13, 2022).
- Beck J, Fielder K. January 2009. Adult life spans of butterflies (Lepidoptera: Papilionoidea + Hesperioidea): broadscale contingencies with adult and larval traits in multi-species comparisons. Biological Journal of the Linnean Society, 96(1): 166–184. doi: 10.1111/j.1095-8312.2008.01102.
- Benyamini D. 2008. Is Euchloe falloui Allard, 1867 (Pieridae) the butterfly with the longest diapause? Nota Lepidopterologica 31(2):293-295.
- Discover Butterflies and Moths, Frequently Asked Questions. Florida Museum of Natural History. (accessed March 14, 2022).
- Ebling FJG. Arthropods. Encyclopedia Britannica. (accessed March 14 2022).
- Flockhart DT, Wassenaar LI, Martin TG, Hobson KA, Wunder MB, Norris DR. 2013. Tracking multi-generational colonization of the breeding grounds by monarch butterflies in eastern North America. Proc Biol Sci. 280(1768):20131087. doi:10.1098/rspb.2013.1087
- French T. Mourning Cloak. Butterfly Atlas Species Accounts. Mass Audubon. (accessed April 8, 2022).
- Kukal O, Dawson TE. 1989. Temperature and Food Quality Influences Feeding Behavior, Assimilation Efficiency and Growth Rate of Arctic Woolly-Bear Caterpillars. Oecologia, 79(4): 526–532.
- Macpherson F. February 10, 2021. What’s the difference between a moth and a butterfly? BBC Science Focus Magazine.
- Mahr S. Black swallowtail, Papilio polyxenes. Wisconsin Horticulture, Division of Extension.University of Wisconsin-Madison. (accessed March 15, 2022).
- Morewood WD, Ring RA. July 1998. Revision of the life history of the High Arctic moth Gynaephora groenlandica (Wocke) (Lepidoptera: Lymantriidae). Canadian Journal of Zoology. doi: 10.1139/z98-085
- Oberhauser K. Monarch Butterfly Frequently Asked Questions (FAQs). U.S. Department of Agriculture. U.S. Forest Service. (accessed March 13, 2021)
- Obregón R, Fernández Haeger J, Jordano D. 2017. Adaptive significance of the prolonged diapause in the western Mediterranean lycaenid butterfly Tomares ballus (Lepidoptera: Lycaenidae). Eur. J. Entomol. 114: 133–139. doi: 10.14411/eje.2017.018
- Patterson B. 2007. Flightless Females. Entomology Hobby Page. Mississippi State University.
- Pohl GR, Patterson B, Pelham JP. 2016. Annotated taxonomic checklist of the Lepidoptera of North America, North of Mexico. Working paper published online by the authors at ResearchGate.net.
- Powell JA. 2001. Longest Insect Dormancy: Yucca Moth Larvae (Lepidoptera: Prodoxidae) Metamorphose After 20, 25, and 30 Years in Diapause. Annuals of Entomological Society of America. 94(5): 677-680. doi.org: 10.1603/0013-8746(2001)094[0677:LIDYML]2.0.CO;2
- Salman MHR, Bonsignore CP, El Alaoui El Fels A, Giomi F, Hodar JA, Laparie M, Marini L, Merel C, Zalucki MP, Zamoum M, Battisti A. 2019. Winter temperature predicts prolonged diapause in pine processionary moth species across their geographic range. doi: 10.7717/peerj.6530. PMID: 30842907. PMCID: PMC6397759.
- Sommer S, Knight D, McDowell S, Burton S, Harker E. The Butterflies of Idaho. (accessed March 14 2022).
- Taylor OR. 2009. Monarch Butterfly Press Briefing. Monarch Watch.