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Phlox Subulata (moss pink) in landscape. Photo © Elaine Mills

The Life Cycle of Butterflies & Moths

Pollinator Week June 20-26, 2022

About Butterflies and Moths – Part 1

By Mary Free, Extension Master Gardener

Monarch Life Cycle–Egg to Chrysalis
Stages of Monarch Development–Egg to Chrysalis.
Photo © Brett Billings/USFWS CC BY 2.0

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.

Luna moth (Actias luna) eggs.
Luna moth (Actias luna) caterpillar.
Luna moth (Actias luna) pupa.
Luna moth (Actias luna) adult male.

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.

Eastern black swallowtail caterpillar before (1:37 pm) and after (1:53 pm) molt. Photos © Mary Free
Newly molted eastern black swallowtail (Papilio polyxenes) late instar consumes its shed outer layer. Video © Mary Free

Pupa Stage

Monarch chrysalis hanging from ornamental grass
Monarch chrysalis attached to ornamental grass with a silk pad and cremaster. Photo © Mary Free

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.

Adult Stage

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)

Adult female luna moth emerging from pupa.
Adult female luna moth with expanding wings.
Adult female luna moth with expanding wings.
Adult female luna moth with hardening approximately 9.5 hours after emergence.

Left to right: Adult female luna moth (Actias luna) emerging from pupa, expanding wings, about 9.5 hours after emergence.

Diapause

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).

Female spongy moth (Lymantria_dispar) with egg mass.
Arctic Woolly Bear Moth (Gynaephora groenlandica) caterpillar.
Eastern black swallowtail (Papilio polyxenes) supported by a silk girdle in October will overwinter
Polygonia interrogationis (question mark)
Monarchs stop to feed on a collarette dahlia late season along their migration path to Mexico

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.

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References

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