2022-23 Monarch Butterfly Winter Numbers Decreased
Every year the Monarch population is estimated by counting the number of hectares (one hectare = 2.5 acres) that contain Oyamel Fir trees inhabited by Monarchs at their central Mexican overwintering grounds. The 2022-23 count which was just released showed a 22 percent decrease from the previous year.
The Monarch population has been declining since counts began roughly 30 years ago. Scientists feel the most important influences are climate change, herbicides and habitat. The weather in the southern United States in the spring, when monarchs are migrating north from wintering in Mexico, is crucial as is summer weather. The creation of genetically modified herbicide-tolerant crops has had a devastating effect on milkweed growth in corn and soybean fields, where it used to flourish. As the Monarchs’ sole source of egg-laying vegetation and larval food, milkweed species are essential to their well-being.
Creating more milkweed habitat appears to be the single most effective way of coming to the Monarchs’ aid. Be it your back yard, school yard, or road sides, disperse those milkweed seeds far and wide! The butterflies that left New England last fall are starting their journey north right now. They will lay eggs and die along the journey, but their offspring will benefit from the efforts we make now. (Photo: Monarchs overwintering on Oyamel Fir trees in the Transvolcanic Mts. of central Mexico; photo and information resource: http://www.journeynorth.org )
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A Monarch’s First Instar
Monarchs, like other butterflies and moths, undergo complete metamorphosis — they have an egg, larva (caterpillar), pupa (chrysalis), and adult stage. During a monarch’s larval stage it eats almost constantly, pausing only to shed its skin. The period between each shedding of the skin, or molt, is called an instar. Monarchs have five larval instars and during their larval stage grow to almost 2,000 times their original mass.
The first meal a monarch larva has is its eggshell and it quickly moves on to milkweed leaf hairs. Soon thereafter it begins to eat the leaf in earnest, often making an arc-shaped cutting.
During this first instar, which typically lasts one to three days, the larva’s appearance changes considerably. When it hatches, the monarch larva is pale green or grayish-white, shiny, and almost translucent. It has no stripes or other markings. It’s about 2 mm long, with front tentacles appearing as tiny little bumps. Its back tentacles are barely visible. By the end of the first instar it begins to have a pattern of black (or dark brown), yellow and white bands, and the 6mm-long body no longer looks transparent and shiny.
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Did you know…
…that mating butterflies face away from each other? (Photo: mating Banded Hairstreaks)
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2nd Brood of Black Swallowtails Emerging
The process of transforming from a caterpillar to a chrysalis is a miraculous one, but it’s especially intriguing when it comes to Black Swallowtails (Papilio polyxenes). For one thing, their chrysalises vary in color from green to brown, depending on the object on which they choose to attach themselves. Equally impressive, while it is still a caterpillar the Black Swallowtail spins a thread of silk from which it suspends itself. It uses this silk sling as support for the chrysalis that is revealed once the caterpillar splits and sheds its exoskeleton (see it dangling beneath the chrysalis).
The second brood of Black Swallowtails (Papilio polyxenes) is already emerging from their chrysalises this summer, mating and laying eggs during their two week adult life span. Look for the caterpillars dining on members of the Parsley family, including Queen Anne’s Lace, dill, parsley, fennel, celery and carrot foliage. (Photos from left to right: Black Swallowtail larva preparing to pupate, chrysalis (with cast off larval exoskeleton) and adult male Black Swallowtail)
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Mourning Cloak Butterflies Mating
Often the first butterfly you spot in early spring is the Mourning Cloak butterfly. Having overwintered as adults under loose bark, Mourning Cloaks are on the wing as early as March. Due to the lack of nectar-bearing flowers at this time of year, these butterflies seek sustenance from the sap of broken branches. They are still present in April and May when mating takes place, after which they die. The next generation emerges as adults in late May or June, feed and then spend July and August in a state of torpor (estivate). They become active in late August or September and again feed before hibernating in the fall.
Mourning Cloaks are referred to as the longevity champions of the butterfly world, as they live up to ten or eleven months. The life span of a butterfly varies greatly among species, but on average most butterflies live about a month. (Note ragged edge of wings, due to old age.)
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Monarch Roosts
Monarch migration is in full swing. Some of the migrating butterflies from the Northeast travel as far as 3,000 miles to reach their winter destination in the Sierra Madre Mountains of Mexico. In addition to finding sources of nectar along their migration pathways to build their fat reserves Monarchs must also seek shelter at night, roosting on land when it cools down and they can no longer fly.
It appears that roosting is critical for migrating Monarch survival. Just before dark these solitary diurnal migrants gather in clusters called roosts. A roost can consist of just a few butterflies up to thousands clinging to leaves and branches on a single tree. Cedar, fir, and pine are common species of trees used for roosts, but deciduous trees are also used.
Most roosting trees are along a principal flyway, located in a cool, moist area, provide shelter from the wind and are near a source of nectar. Often roosts last for only a night or two but can last a week or two. Monarchs can but do not necessarily use the same resting sites year after year. It’s generally accepted that these roosts are an anti-predation tactic, employing the strategy of safety in numbers. To see a map of documented 2021 roosts, go to Journey North’s site: https://maps.journeynorth.org/map/?map=monarch-roost-fall&year=2021.
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Mourning Cloak Caterpillars Pupating
Having overwintered as an adult, the Mourning Cloak butterfly (Nymphalis antiopa) is one of the first butterflies seen in early spring. Mating takes place and eggs are laid in a cluster encircling a twig of a willow, cottonwood, elm, birch or hackberry tree. The hatching caterpillars stay together until they move off their host plant to pupate, which is what is happening right now and why you can find these distinctive spiny black and red caterpillars at this time of year. Adult Mourning Cloaks emerge in midsummer, enter a state of dormancy until fall and then seek a sheltered spot in which to hibernate until spring.
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Mourning Cloak Butterflies Emerging
With the recent warm temperatures, Mourning Cloak butterflies have been seen gliding through fields and leafless woods. Unlike most butterflies, Eastern Commas, Question Marks, Red Admirals and Mourning Cloaks overwinter as adults, seeking shelter in protected spots such as under loose bark. When spring arrives, they slip out from their winter quarters and take to the air.
Mourning Cloaks resemble dead leaves so much that from a distance the entire insect seems to disappear when it lands on the forest floor. Up close you can see the velvety texture of the wing scales, said to resemble the clothing mourners used to wear; hence, their common name. Mourning cloaks live up to ten months — an impressive life span for a butterfly. As they age, the yellow border of their wings fades to an off-white.
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Cabbage Whites Mating
Cabbage White butterflies (Pieris rapae) are seemingly common, rather ordinary and unremarkable butterflies. That is, until you become acquainted more intimately with their reproductive idiosyncracies. The male’s sperm, along with a nutritious snack, is contained within a package called a spermatophore. It is the size of the spermatophore that defies belief, as it makes up 13 percent of the male’s body weight. Translated into human terms, a 150 male would possess a 20-pound package of sperm.
The male Cabbage White deposits its spermatophore into a pouch within the female’s reproductive tract and the sperm proceed to swim to a second pouch where they are used to fertilize the female’s eggs. The female absorbs the nutrients that accompanied the sperm and uses them to make approximately half the eggs she lays.
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Canadian Tiger Swallowtails Puddling
In April, during mud season, living on a dirt road can be a curse. But in May and June, when swallowtails emerge, it can be a blessing as you often witness a phenomenon called “puddling.” This phenomenon consists of clusters of butterflies (predominantly males) gathering to obtain salts and minerals that have leached from the soil into standing puddles and moist dirt.
Because butterflies do not have chewing mouthparts they must drink their meals. While nectar is their main source of nutrition, males often supplement their diet with minerals. The sodium uptake aids in reproductive success, with precious nutrients often transferred from the male to the female during mating. This extra nutrition helps ensure that the eggs survive.
Pictured are Canadian Tiger Swallowtails puddling. They are easily mistaken for Eastern Tiger Swallowtails as they look very much alike and their ranges overlap. To determine which you have seen, look at the underside of the butterfly’s forewing and see if the yellow band along the margin is solid and continuous (Canadian Tiger Swallowtail, Papilio canadensis), or if it is broken up into spots (Eastern Tiger Swallowtail, Papilio glaucus).
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Monarchs Splitting Exoskeleton For The Fifth And Final Time
In the Northeast there appears to be an amazingly large number of Monarch larvae this year, and most of these larvae will complete their metamorphosis by transforming into a beautiful green chrysalis. Once mature, the larva, or caterpillar, wanders about and finds a suitable spot (usually protected and stable) to spend the next two weeks hanging precariously in the wind. It then spins a silk mat in this location, and puts a silk “button” in the middle of the mat. It clasps the button with its last set of prolegs (it has three pairs of true legs, and five pairs of so-called prolegs) and spends about 18 hours hanging in a “J,” with its head down, preparing to split its exoskeleton for the last time and reveal the chrysalis within it.
Ba Rea, a Monarch specialist (and publisher of my children’s book, Milkweed Visitors), informs her “Monarchchaser’s Blog” (https://monarchchaser.wordpress.com/about-monarchs/) readers that even though the visible changes between the larval and pupal (chrysalis) stages of a Monarch are sudden, inside the caterpillar these changes are taking place gradually and long before we can see them. “The parts that will transform the caterpillar into a butterfly are present from the time that the egg hatches. Inside the caterpillar are “imaginal disks.” As wonderfully fanciful as the word imaginal sounds, it is actually referring to the adult stage of the monarch which is called the imago. These disks are the cells that will become the butterfly’s wings, legs, proboscis and antennae, among other things. By the time the caterpillar is half an inch long its butterfly wings are already developing inside it. “
After eight to fifteen days, the adult Monarch emerges from its chrysalis and heads towards Mexico (butterflies that emerge after the middle of August migrate). It is the great grandchildren and great great grandchildren of these migrating monarchs that will return next summer. (Photo: Monarch hanging in a “J” from Jewelweed, also known as Touch-Me-Not — not the sturdiest of plants to hang from!)
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Survival Through Mimicry: The Viceroy Butterfly
The survival of Viceroy butterflies in all of their life stages is significantly enhanced by mimicry. A Viceroy egg resembles a tiny plant gall. Both larva and pupa bear a striking resemblance to bird droppings. And the similarity of a Viceroy to a Monarch is well known. For years it was thought that this mimicry was Batesian in nature – a harmless organism (Viceroy) mimicking a poisonous (Monarch) or harmful one in order to avoid a mutual predator. However, recently it’s been discovered that the Viceroy butterfly is as unpalatable as the Monarch, which means that mimicry in its adult stage is technically Mullerian – both organisms are unpalatable/noxious and have similar warning mechanisms, such as the adult butterfly’s coloring.
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Monarch Butterfly Larvae Are Cannabalistic
The very first meal that a Monarch Butterfly caterpillar eats is its own eggshell. In order to hatch, it eats its way out of the egg, and then polishes off the remainder of the eggshell. It then starts to wander around the leaf and if it finds another Monarch egg, it will start to eat it.
Female Monarch Butterflies lay 300-500 eggs over two to five weeks of egg-laying. Normally, a Monarch only lays one egg at a time (on the underside of a tender, young milkweed leaf). It is fairly rare to find more than one egg on a leaf, or even on the same plant. After a female lays an egg, several seconds up to a minute goes by before she lays another egg (referred to as a refractory period). During this time she usually moves on and finds another milkweed plant on which to lay the next egg. This lapse of time between the laying of each egg probably evolved to discourage the laying of multiple eggs on one leaf and to encourage the dispersal of a female’s eggs on different milkweed plants so as to decrease the chances of cannibalism occurring.
According to Dr. Lincoln Brower, renowned Monarch entomologist, a cluster of Monarch eggs on any given milkweed leaf indicates that either milkweed is in short supply, or the female that laid the eggs is either sick, very old or she has been flying for a very long time and several eggs have matured.
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Black Swallowtails Laying Eggs
Looking every bit like the Golden Alexander (Zizia aurea) flower buds on which they were laid, the pale yellow eggs of a Black Swallowtail (Papilio polyxenes) are next to impossible to find unless one is fortunate enough to see them in the act of being laid. Members of the parsley family (Golden Alexander, Wild Parsnip, Queen Anne’s Lace, Dill, Carrot) are host plants for most ravenous Black Swallowtail larvae, and thus that is where you will find their eggs. As they eat, the caterpillars absorb toxins from their host plant, which does not harm them but makes them distasteful to avian predators.
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A Butterfly’s Proboscis May Act More Like A Paper Towel Than A Straw
The chewing mouthparts of a butterfly larva, or caterpillar, undergo changes when the larva develops into an adult butterfly. They are turned into a tube consisting of two parts, or galeae, that when joined form a structure called a proboscis. The proboscis looks like a straw, and has long been thought to act like one. It is often referred to as a sipping tool through which nectar is obtained by butterflies. However, recent discoveries have scientists thinking that the proboscis works more like a paper towel than a straw.
The liquid that a butterfly feeds on in addition to nectar – animal tears, juice inside decomposed fruit, tree sap, sweat, liquid contained in scat – is so viscous that sipping or pumping it through the proboscis, or feeding tube, would require an enormous amount of pressure. It’s been suggested by entomologist Konstantin Kornev of Clemson University that butterflies draw liquid upwards using capillary action – the same force that pulls liquid into a paper towel. The proboscis actually resembles a rolled-up paper towel, with tiny grooves that pull the liquid upwards along the edges, carrying along the bead of liquid in the middle of the tube. (Photo: Sulphur Butterfly on New England Aster)
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Viceroys — Master Mimics
A plump caterpillar is irresistible to many insect-eating birds, and some of them (notably Viceroys and Giant Swallowtails) have outfoxed their predators by assuming the appearance of bird droppings, which one assumes is a far less appealing meal. They do this using color, pattern, choice of resting place and even position – contorting their bodies to match the shape of bird droppings. The Viceroy (Limenitis archippus) uses this technique during its later larval and pupal stages.
The adult Viceroy butterfly also uses mimicry to enhance its survival, but it mimics another butterfly — the Monarch — not bird droppings. Both the Viceroy and the Monarch are unpalatable and contribute to each other’s protection from birds with this strategy, a relationship known as Mullerian mimicry.
In New England there can be up to three broods of Viceroys, with the larvae of some of the second brood and all of the third brood overwintering and pupating in the spring.
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Eastern Black Swallowtails Laying Eggs
Eastern Black Swallowtail (Papilio polyxenes) butterflies are mating and laying eggs. The female Eastern Black Swallowtail can appear quite frantic as she visits multiple host plants just long enough to leave a very tiny, spherical, pale yellow egg before heading on to the next plant. In the wild, Queen Anne’s Lace, Wild Parsnip, Golden Alexander and Poison Hemlock are favorite host plants; in vegetable gardens you frequently find larvae (if you should miss the eggs) on dill, fennel and parsley. Entomologists have found that host plant odor is one of the cues involved in the Eastern Black Swallowtail’s choice of where to lay eggs.
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First Brood of Pearl Crescents Emerging
The first of this summer’s broods of Pearl Crescents are maturing. Our smallest and most common black and orange butterfly can be found throughout the eastern half of the U.S.. This particular species is named after a crescent-shaped spot near the margin of the hind wing on the underside. Its wingspread is about an inch and a half. The exact pattern on its wings is highly variable, making it challenging at times to distinguish it from other crescents.
Asters are the primary food source of Pearl Crescent larvae. Mated females lay their clusters of 20-300 green-yellow eggs on aster leaves, and in roughly a week the brown, black and white spiny larvae emerge. Two broods are common in the Northeast, so one can continue to look for crescent caterpillars on asters into August. Note: The Northern Crescent is very similar-looking to the Pearl Crescent (it may not even be a distinct species). Photo could be of either species. All lepidopterists welcome to comment!
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Adult Butterflies Emerging, Mating & Laying Eggs
Butterflies that remain in New England during the winter spend it in one of many stages – some as eggs, others as larvae or pupae, and a few as adults. Mourning Cloaks, Compton Tortoiseshells, Milbert’s Tortoiseshells, Question Marks, Gray Commas and Eastern Commas all overwinter as adult butterflies. They store fat in their bodies in the fall and replace a portion of the water in their blood with an antifreeze agent, which prevents the lethal formation of ice crystals in their bodies. These butterflies then slip into cracks, behind loose bark, in a hollow tree or some other sheltered spot where they enter a stage referred to as winter diapause. Metabolic and respiratory rates are greatly reduced, and the butterflies remain inactive until the warming, lengthening days of March and April, when they emerge to mate and lay eggs. They often look rather tattered, as they put many miles on their wings the previous summer. Unlike most adult butterflies which live only a few weeks, butterflies that overwinter as adults have a lifespan of eight to ten months. (Photo: Eastern Comma – note white “comma” on under side of hindwing)
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Painted Ladies On Their Way
For the past few weeks we have been witnessing the migration of thousands of southward-bound orange butterflies, a vast majority of which are not Monarchs (although they are having a good year, too) but Painted Ladies (Vanessa cardui). Both their large numbers and the length of time that they have lingered in the Northeast this fall are unusual.
This was a good year for Painted Ladies — they migrated north earlier than usual, arriving in mid-April, possibly giving them time to have an extra generation, reproducing twice instead of once during the summer. In addition, the unusual weather we’ve been having has not been great for migrating. The butterflies have spent a lot of time fueling up on nectar while waiting for a wind out of the Northeast to assist them in their flight to the Southwest. With the prevailing wind change we’re now experiencing, it’s likely many of them will resume their migration today.
Mourning Cloaks Surviving On Sap
Who doesn’t celebrate at the sight of a Mourning Cloak butterfly gliding through the woods on soft, spring breezes? Because the adults spend the winter hibernating behind loose bark, Mourning Cloaks are among the first butterflies to take flight in the spring. Most butterflies overwinter as eggs or pupae inside chrysalises, and have to complete metamorphosis before they can take to the air.
Surviving in March and April, when there is little, if any, nectar to be found, is challenging. Mourning Cloaks sustain themselves with the sap that exudes from broken tree branches or wounds in tree trunks. Oaks are their preferred source of sap. When they find some, they walk down the trunk to the sap and feed head downward (see photo).
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First Monarchs Have Arrived At Wintering Sanctuaries
During the first two weeks of October, south winds prevented migrating Monarchs from making a lot of progress on their flight southward. Cold fronts were weak during this time, and wind blew from the north infrequently. On Oct.12 this persistent weather pattern broke, headwinds subsided and thousands of Monarchs were seen migrating through Texas. By Oct. 20 the first Monarchs entered Mexico and by the 23rd the first butterflies had reached their wintering grounds. Follow their progress as they continue to stream across northern Mexico, headed for their sanctuaries, at http://www.learner.org/jnorth/maps/monarch.html.
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Greater Fritillaries
There is a group of butterflies known as greater fritillaries, or silverspots (their underwings often have multiple silver spots). Three species of greater fritillaries can be found in the Northeast: Great Spangled, Atlantis and Aphrodite. All three are similar in appearance, with differences so subtle that the butterfly in a Naturally Curious post last month was mis-identified as a Great Spangled Fritillary, when it was actually an Atlantis Fritillary. Thanks to a sharp-eyed reader, Sue Elliott, this was brought to my attention. If you can approach a fritillary close enough to see the color of its eye, identification is a snap! Great Spangled Fritillaries have amber-colored eyes, Atlantis Fritillaries have blue-gray eyes, and Aprhrodite Fritillaries have yellow-green eyes. Can you identify the two species of fritillaries that are pictured? (Upper right, on thistle – Great Spangled Fritillary; main photo, on Joe-Pye Weed – Atlantis Fritillary)
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Eggs Of Migrating Generation Of Monarchs Hatching
The Monarch eggs that are hatching now contain the larvae that will metamorphose into the butterflies that will migrate this fall to central Mexico. Unlike earlier-hatching generations that only live six to eight weeks, the Monarchs that result from late summer and early fall hatchings live six to nine months. Part of the reason for this difference in life span is that, unlike the earlier generations that mate soon after emerging from their chrysalides, late-hatching Monarchs postpone mating (reproductive diapause) until the end of winter, thereby conserving energy for their two to three thousand-mile, two-month migration. (Photo: monarch larva’s first meal – its eggshell.)
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