Better late than never, Gentle Readers. I can't even blame the time it took to write this study of the popular Pipevine Swallowtail on browser updates, weather-related connection disruptions, and other cybergarbage. There is a lot of good, informative material on the Internet about this species. Research at the level it takes to produce a short article about a more obscure species could easily produce a book about philenor. I sat down to write this post on Thursday evening, and here it is, well past sunset on Friday night.
And the next butterfly on the list is also well known, well documented, and furiously popular. at least in the Western States. But this one's popular in the East as well.
For at last we've come to a North American butterfly, and a beloved one--Battus (or Papilio) philenor, the Pipevine Swallowtail. If Americans have any interest in butterflies, we probably know this one. To know it is to love it. "Extraordinarily beautiful," science writers enthuse. It's most common in the southern tier of States, but has been seen in southern Canada, is fairly common in Mexico, and is found as far south as Guatemala.
Bloggers like them. Quite a gallery of photos of philenor and other species has built up at
It's easily confused with a few other American swallowtails in much of its range, though--because a few species that are less toxic to birds mimic philenor. As a child I learned to confuse Pipevine Swallowtails, Spicebush Swallowtails, dark female Black Swallowtails, and dark female Tiger Swallowtails, all of which my elders referred to as "black Swallowtails," because their base color is black. Tiger Swallowtails were clearly different. Their affinity for some of the larger "black Swallowtails" could not be ignored; my brother reported that a teacher had told him that Tiger Swallowtails mated with "black Swallowtails" to produce "Royal Swallowtails"--by which they meant the male Black Swallowtail, which has more yellow and less black on its wings than the Pipevine Swallowtail and its mimics. This is the kind of thing that drove the old naturalists to drink and Latin. Common names are useless and misleading, they said. To talk accurately about living creatures we should use Latin names.
(Photo of Battus philenor hirsuta donated anonymously to Butterfliesofamerica.org. Not all of the subspecies hirsuta show the purplish iridescence seen here, even in the same light, but the bodies do look thicker and blacker than other philenor because they have dense, fluffy fur. This subspecies' name at least makes sense: hirsuta is Latin for hirsute, or hairy.)
So they named this beloved butterfly, originally, Papilio--Latin for "butterfly," Linnaeus having regarded the Swallowtails as the quintessential butterflies--philenor, Greek for "lover of her husband," an ideal rather than the name of a character in ancient literature. Very scientific. Very objective. Butterflies don't form pair bonds, and at least half the species are male.
(Photo of Battus philenor acauda from Butterfliesofamerica.org. Acauda means "tailless," though this Yucatan subspecies usually has a vestigial "swallowtail." Rothschild described the vestigial "tails" by saying that "the tail has become a tooth.")
Then, some years later, after many species of butterflies had been named Papilio something or other, scientists chose different names for genera that might actually be able to hybridize, and arbitrarily named the group that includes philenor after Battus, an ancient king whose name is probably related to our word "battle" and probably meant "warlord," or a shepherd in an ancient cautionary tale who shared the same name. Right. So in Latin this butterfly is the Warlord Lover-of-her-husband. It's not the butterflies who are gender-confused...
(Photo of Battus philenor insularis from Efrenbiologia, Isla Clarion, August 2016, showing that the genders are confusible to humans. Some males are much bluer than females, and some couples look about the same. Since the butterflies smell each other's scent they don't seem to be confused at all. Insularis, of course, means "of the islands," the Tres Marias Islands and Nayarit.)
In Spanish "Swallowtails" are Mariposas de cola golondrina, and this species are simply azul, the Blue Swallowtails. Some people like to call them Blue Swallowtails in English, too.
(Photo of Battus philenor orsua from Sineadgmz, Mexico, January 2024, donated to Inaturalist.org. Orsua is a family name; no source explained whose or why.)
All Pipevine Swallowtails eat pipevine, the North and Central American species of (you surely guessed it) Aristolochia, while they are caterpillars. They are most often found in warm forest country where these vines grow, and are occasionally seen almost everywhere. They're not all alike; if you get a good look in a good light you may be able to tell which of a pair is male (his wings are usually a brighter iridescent blue) and even identify the five recognized subspecies. Butterflies of the Pacific Northwest says that "The amount and shade of blue varies with individual, gender, age, angle, and intensity of the light," and describes the shading on the outer underside of the hind wings as "metallic" or "Mylar blue" with "persimmon red," black-rimmed spots. The upper side of the hind wings, when visible, can appear like a flash of bright sky blue, with a border of white spots. The body is black, sometimes with an iridescent blue sheen in males, fading to gray more typically in females. They are one of several butterfly species that can look different depending on the temperature in which they grew up, though philenor don't vary so widely as to have been mistaken for separate species. When Battus philenor philenor survive pupation through a frosty winter in the northern part of their range, according to the University of Kansas' Manual of Kansas Butterflies, they mature with smaller wings and furrier bodies and look more like Battus philenor hirsuta; but the California subspecies look "hirsute" all year.
In addition to the other Swallowtails in its range, Battus philenor also seems to be a "model" for the Red-Spotted Purple and Diana Fritillary. Far less toxic to birds, they can be mistaken for philenor from a distance and thus discourage birds from eating them too. The blue color delights the human eye but its purpose seems to be to warn birds, "You do not want to eat me."
US-based search engines actively favor US over foreign sites, with amusing results when one is searching for documents about a multinational butterfly species. B.p. philenor, the original and most common subspecies found in Florida and Texas, is abundantly documented online. B.p. hirsuta is well represented. B.p. acauda, usually found in Mexico and Central America, is less documented, and it can be hard to find photo documentation of the subspecies orsua and insularis, native to islands and found in some parts of Mexico. Google seems positively averse to displaying documents of orsua and insularis in Spanish and tries to drag you back to better sponsored documents of B.p. philenor in Texas even when you've typed "battus philenor in mexico" into the search bar.
Subspecies acauda can have quite a distinctive look, with different spots on the underside.
Photo by Alex_cb, Quintana Roo, August 2023, donated to Inaturalist.org.
The upper side may be more likely to look black and white , though this subspecies can also flash "cobalt blue" hindwings in the right light.
Photo by D99, Quintana Roo, November 2017, donated to Inaturalist.org.
The species had been recognized and written about even before Linnaeus. The earliest naturalists gave it some of those sprawling, inconsistent Latin names Linnaeus set out to simplify. It was Papilio eques trojanus philenor in 1771, when Linnaeus used that name, which he later shortened. "Butterfly Trojan-Horse Lover-of-her-husband"? "Trojan Horse" might have referred to its confusibility with mimic species.
What Linnaeus knew about philenor in 1771. Digitized images of these very old studies are preserved at funet.fi; this screenshot was taken by Dennis Walker at socialbutterflies.com.
By the 1890s, when Walter Rothschild wrote his description of this species, he couldn't resist speculating about how the different Battus species had evolved into one another. His ramblings can be found at https://archive.org/details/novitateszoologi13lond/page/509/mode/1up?view=theater. He didn't actually know what might attack these butterflies, but he was full of theories about what :must" now or "must have" once eaten them, to explain the facts that most of them have "swallow tails" but some don't, and most look relatively smooth but some look very furry. He didn't even bother to mention their size range, except to mention that the first generation to fly in spring are smaller than their offspring who fly in summer. (Wingspans can be up to four inches, though three inches is probably more common. Some individuals' wingspans are barely over two inches. However, some South American individuals have reportedly had wingspans up to five inches. In places where they coexist with Tiger Swallowtails they're likely to be described as "smaller and bluer" than the bolder, more familiar female Tigers.)
Rothschild's article mentions, with a nugatory question mark, Reakirt's having classified philenor as a Pachliopta. In fact the mostly South American Battus Swallowtails are similar in many ways to the south Asian Batwings, but their bodies are black, not red. However, though forewings and hindwings move together when they fly, philenor's flitting-and-sipping behavior does show a very limited counterpart to the Pachliopta species' ability to move their fore and hind wings independently; they can keep their forewings moving to maintain balance in the wind while holding their hind wings open to display their social status (see below) to one another. Scientists now describe the similarities among Battus, Pachliopta, Atrophaneura, and other genera by putting them in the "tribe" Troidini, the Aristolochia-eating butterflies.
Photo donated to e-butterfly.org by Billtebird, showing the forewings raised and fluttering while the hind wings remain spread out and relatively still. The butterfly and flower are probably moving together in the wind. This exposes the hind wings to light at different angles and shows the other butterflies that this one's not fading to gray or green.
As with other Battus, the forewings are long and the hindwings can be hidden when the butterfly comes to rest; they can look almost like the Longwing family.
Photo by Dandewild at e-butterfly.org.
And when do they fly? Rothschild didn't say, but the fact is that at any time of year a Pipevine Swallowtail is probably flying somewhere. There are distinct generation groups during a year in places where the species is active all year. In some parts of Mexico they're found in winter; in the Northern States and Canada they're found in summer. Here's a chart showing when to look for them in your State or province:
More recently, since the butterflies are common in countries that can afford to fund scientific research, many peculiar studies of them have been made. It has been formally determined, for example, that females who are carrying more eggs focus more intensely on finding places to lay eggs and are less choosy about where they lay their eggs than females who have already unloaded some of their eggs are. The eldest caterpillars in one brood thus have to take what they can get in the way of a home, while the younger siblings' homes are likely to be carefully selected. Older siblings may grow up as a family group of a dozen or more, while younger siblings may be solitary.
Another topic of serious scientific study has been the extent to which philenor search visually for the right leaf shape when looking for vines to lay eggs on. It turns out that the butterflies do look for the right leaf shape. In places where they have a choice of different Aristolochiae with longer or wider leaves, a butterfly who has laid her first few eggs on one of the two possible food plants is likely to look for other vines of the same species. However, the final decision is determined by palpating the leaves with her feet, which contain receptors for chemicals the butterflies probably sense as tastes. By walking on a plant a mother butterfly can determine whether it will taste good and be nourishing for her caterpillars when they hatch.
Mark Rausher, who studied butterflies' use of sight to find the kind of plants on which to lay eggs, went on to study the biochemical properties they seem to look for. This study is new enough that you may need to buy it if not reading it at school. (This web site was founded partly for the use of students and has determined, over the years, that a a significant part of our readership does come from schools, as is shown by the decline in readership when schools close. This web site warmly encourages high school readers to nag your school libraries to offer more scientific journals instead of cartoonish video games.)
Speaking of school libraries, some of them are now offering free printable PDF copies of the pricey Swift Guide to the Butterflies of Mexico.
And some scientists have identified (some of) the biochemicals mother philenor butterflies look for:
Color is a factor in adult butterflies' nectar-seeking preferences; they like pink and purple. They visit white, yellow, and red flowers too, but tend to visit pink and purple ones first. This is primarily a pollinator species, but, as in many Swallowtail species, males drink mineral-heavy, brackish water and females prefer, if they can, to meet their need for dietary minerals by contact with males. Philenor are generally less attracted to dung and carrion than some Swallowtails, but males do like fresh horse and cattle droppings
Photo from CarolinaNature.com, donated by Will Cook.
A study found that Battus philenor normally pupate for either 11 or 12 days, and almost always emerge from the pupal shell at sunrise.
A study found that the butterflies like to perch, at night, in small uncrowded groups. In addition to this badly formatted study supplied to the Internet by the Smithsonian Institution, this observation has been documented in a Youtube video that I found blurry and hard to watch, despite some nice clear still shots of individual butterflies sleeping motionless, wings spread out to catch the sunlight at sunrise, perched on tall grass and flowers on the prairie.
Sleeping in small uncrowded groups starts in late caterpillar-hood, when individuals often leave their food plants and spend the night somewhere else--where they expect predators won't look for them, no doubt. For caterpillars they can move fairly quickly, tapping their antennae on the surfaces ahead and beside them as an aid to navigation. Caterpillars do have working eyes, not on the sides of their heads where the jaw muscles and camouflage markings are likely to be, but down near their mouths; species tested were found to be very nearsighted, seeing less than a yard ahead. Humans who are so nearsighted are "legally blind," so the resemblance of a caterpillar tapping the path with its antennae to blind people tapping the ground with white canes is not only superficial. Toxic and relative bold though they are, they are vulnerable while resting at night, and awaken with a visible start.
Being so creatively ugly, of course, the caterpillars can give humans a start when the places they choose for resting away from their food plant are humans' homes. This photo of a caterpillar on a narrow window frame makes it look as if the house is being invaded by an alien monster. Actually the caterpillars tend to pupate while they're less than two inches long.
Photo by Lfelliott, Columbia, Missouri, July 2019, donated to Inaturalist.org.
Colors have been chemically analyzed:
Some of the color variations that are possible at all life stages for this species may be hereditary; some are produced by climate conditions; others may be produced by variations in the quality of their diet.
The social effects of these butterflies' colors have also been studied. (Butterflies are most fertile the first time they mate. Female Swallowtails actively watch males, preferring virgin bridegrooms and watching for fresh young males to mature, since females in many species are fertile when they crack their pupal shells but males have to wait for hours or days to become fertile. Males whose iridescent scales have been deliberately worn down by researchers had a hard time finding mates. The researchers weren't sure whether the females thought the worn-looking males looked too old, looked like a different species, or--a possibility the researchers didn't mention--looked too damaged. When we see a man with a part of his normally visible surface scraped off, do we think "He's handsome" or "He's ugly," "He's old" or "He's young," or do we think "Oh dear, what happened to him?" Too many of these studies are done by guys.)
Photo by Kelly Jacobs on Pinterest. He looks fine to humans, but is that blue on the greenish side?
Young males hang out with other guy-butterflies, showing off and sometimes competing to hold the highest territory on a hill. When they fly toward each other, nobody ever gets hurt; what they're threatening to do is embarrass each other by showing superior size, speed, and skill. (As Walt Kelly observed, a butterfly is an adult caterpillar, and might not want to admit it is completely harmless--but it is, anyway.) They chase each other away from their territories and chase females, too. If a female is interested in a male, the chase was found to last, on average, about half a minute before the couple mated. The benefit of earning a degree in entomology is that you get paid to hang out in places where you can see things like this. The cost is that you actually have to watch and count things like this...
Gatherings of male Swallowtails aren't always territorial displays. Since several species of male Swallowtails like the same mineral salts, they often become the core of a large mixed group of drinking buddies that includes several smaller species as well.
Photo by Jeff Pippen from North Carolina.
Female Swallowtails visit these groups to check out the males, but males can't always rely on females to start the courtship process. They may spend many minutes flying around females, showing their colors and scents, before getting a favorable response or losing hope of one. They will mate more than once in their short lifetimes, if they can.
In this initially confusing photo from AnimalDiversityWeb, a Pipevine Swallowtail and a Tiger Swallowtail, both apparently old males, seem to be drinking from the same wet sand:
To humans the Pipevine Swallowtail may resemble a female Tiger the Tiger Swallowtail chased when he was younger. Since butterflies recognize each other by scent, the Tiger Swallowtail is unlikely to make that mistake. They're just two old fellows fading away together, the Tiger with half his left hindwing gone. The female Tiger, bigger and more colorful than the Pipevine Swallowtail, cleaner and more polite than her mate, has presumably flitted off into the woods to lay her eggs in the tops of tulip poplar trees.
In many Swallowtail species females are bigger than males. In philenor some photographs of couples show no size difference, and the rule that males have darker black and brighter blue colors doesn't always hold true either. Below, the one with the egg-stuffed body shape is also the one whose wings show more blue.
Photo donated by Robberfly to Inaturalist.org: subspecies hirsuta in Sausalito (California) in March 2019.
In fact, one study suggests, male philenor hindwings iridesce more "true" blue before mating and a greener shade of blue after mating. Since butterflies don't form families, males will try to mate again right after their original mate flits off to look for lots of different vines on which to distribute her eggs, but these matings are likely to be less fertile--so females avoid those secondhand males.
Females can look grayish or brownish (as can males, in some lights--it's really hard to tell, except that the ones you see laying eggs are female) but only in a reddish sunset light can they iridesce purple, as in this photo. I suspect Bill Hubick of having used a colored light to enhance this beauty:
As she sips from the Monarch's favorite flower, does she fantasize about being a queen? No, that's a strictly human fantasy. Two more views of Madame Butterfly at https://www.billhubick.com/photos/butterflies/pipevine_swallowtail.php .
Males' fluttering around females displays their blue color from as many different angles as possible, ensuring that females can pick out those true blue colors:
Their DNA has been studied:
Encouraging the appropriate (preferably native) host plants and not spraying "pesticides" outdoors have been found effective in checking local population declines. Butterfly populations come and go, as their microscopic predators follow their population trends, so it may be good for the species overall if the local population shifts from one neighborhood to another every few years. When an overall decline was confirmed in California, conservation efforts seemed to help:
But beware of introducing exotic Aristolochia species. There are some Aristolochias that philenor can't eat. Occasionally a female will lay a few eggs on an exotic vine that will actually be toxic to her caterpillars.
This Aristolochia elegans can become an invasive nuisance in Florida and California. Philenor caterpillars hatched on it will not survive. It's native to Brazil, but Google didn't show any species of Swallowtail butterfly that could eat it. When introduced into Australia it was blamed for killing the Richmond Birdwing butterflies there.
This Aristolochia serpentaria, a.k.a. snakeroot or birthwort, is the primary food plant for Battus philenor in the Eastern States. Photo from Mary Lee Epps at the Virginia Native Plant Society, vnps.org. Its flowers are smaller and harder to find than those of the invasive nuisance species but, if you look closely, they have a similar little burst of dark reddish color inside;
Aristolochia macrophylla, a.k.a. pipevine or Dutchman's Pipe (and most Aristolochias seem to have been sometimes called birthwort), is another food plant for Battus philenor philenor.
Aristolochia californica is the natural food plant for Battus philenor hirsuta.
Aristolochia pentandra is the natural food plant for Battus philenor acauda.
Aristolochia or Isotrema tomentosa is another plant some Battus philenor can eat.
These photos were selected for showing both leaves and flowers. In real life Aristolochia vines consist of a lot more leaves than flowers, and people often don't recognize them because, while stepping over vines in the woods, they never notice the flowers. The University of Florida offers more detailed information about the plants these caterpillars can and can't eat.
When newly eclosed butterflies stretch out their wings for the first time, females contain considerably more aristolochic acid than males. Over the next ten to fourteen days, as they mature, reproduce, age and die, males remain as toxic as ever while females become less toxic. Apparently the female's extra dose of aristolochic acid goes into the eggs. She keeps enough to remain toxic to birds all her life.
Some sources claim that in the Philippine Islands this species is believed to bring bad luck. Well, it would be bad luck if this American butterfly became an invasive nuisance in the Philippines and displaced native Atrophaneuras, some of which are rare and endangered, so that belief might make more sense than many superstitions do.
How do people get these butterflies to perch on their fingers? When the air drops below a certain temperature, all butterflies go into hibernation mode. If gently picked up and carried into a warmer place, they will wake up slowly on your hand, looking as if they were asking themselves what the bleep is going on, but not injuring themselves in a frantic effort to escape. Their instincts tell them to let themselves warm up, quietly, and they'll soon be able to fly away. So they rest calmly on your hand, absorbing warmth, stretching their long legs and tongues, fanning their wings, and giving you time for a photo or video shoot before they fly away.
Caterpillars don't seem to see far enough ahead to be able to see that a human is a living creature; when they crawl around on us they're probably trying to figure out what can have so many different textures and odors. Butterflies do see us as entire living creatures, but they don't seem to understand the concept. If we grab them or box them in, we're predators and they'll tear themselves to pieces trying to escape from us. If we sit still, some male butterflies may actually think traces of soap and sweat on our skin taste interesting, and may stroll around licking us. (Female butterflies won't be interested unless we happen to be holding something like a juicy melon rind.) If they wake up from hibernation mode to find themselves sitting on our fingers, and we hold still, they'll continue waking up with the semblance of serene faith it seems to require for anything as fragile as a butterfly to live.
It's easy to attract a philenor family to a shady corner of the garden, according to MyGardenerSays.blogspot.com. If unable to transplant a native Aristolochia vine from the woods, you can probably buy A. fimbria as a ground cover from a garden shop. It' has attractive white-veined, pale green leaves and a nice symbiotic relationship with these butterflies. The caterpillars seem to eat it all up. Then it grows back. Then the next generation of caterpillars seem to eat it all up...The blog post goes on to discuss other plants and butterflies that coexist with philenor in the blogger's part of Texas.
Eggs are most often described as orange-red, sometimes orange or amber, and sometimes even burgundy. Like the eggs of other Troidini, they're little round beads textured with drops of aristolochic acid that protect the eggs from being eaten by ants.
Photo by Ansel Oommen, Bugwood.org.
Hatchling caterpillars...
Photo from thedauphins.net .Photo essay showing the full life cycle at http://www.thedauphins.net/id111.html .
Caterpillars are most often black or a dark purplish color fashionistas call aubergine (it literally means eggplant-colored, but is used to refer to a brighter shade than actual eggplants). However, as Birdgal5 documented in this photo (May 2008, Folsom, photo donated to Inaturalist), even young ones can have the minority bright red coloring. Whether caterpillars look black, aubergine, brown, or red may depend on how much light they've been exposed to; since most of them live in the woods, on the undersides of vines, they see relatively little sun and look black.
If, and only if, you eat too much red licorice and want to turn yourself against this candy, click here. I am not agreeing with the blogger's claim. I'm only saying that thinking about it is a good way to form an aversion to red licorice. Or cinnamon "red hots." Or lipstick!
Despite their dragonlike look (and they can chomp, if not hard enough to puncture the skin at least hard enough that you could feel the pinch), these caterpillars are harmless to humans--unless a human, perhaps an infant, was foolish enough to swallow one. Aristolochic acid has been consumed by humans for medical purposes but its effects aren't pleasant. If you weren't looking for relief from something even less pleasant, you'd regret having ingested this plant toxin. It raises pulse and respiration to a degree reported to involve dizziness, nausea, and violent expulsive contractions, as in its old herbal name "birthwort." Modern obstetricians usually prefer other chemicals even to speed up the birth process. Even Klaus Schwab would never recommend that anyone eat zis "bug."
This scene, not found in nature, was staged by Ansel Oommen, Bugwood.org. A Pipevine Swallowtail caterpillar, munching away at a pipevine leaf, has been posed next to a Monarch caterpillar, munching away at a milkweed leaf. Though very different the caterpillars are similar in size and have similar tentacles. Both are completely harmless to humans, crops, livestock, and gardens...unless swallowed.
The tentacles, some researchers say, may help the caterpillars find edible leaves:
In natural conditions Monarch caterpillars never grow up in family groups, have no social instincts, and are likely to try to eat one another if they do meet. Several of the larger caterpillars behave this way; it's one way nature keeps them from overpopulating and destroying their host plants. In nature, however, philenor often grow up in small family groups, as butterflies often lay the first few eggs in clusters, and siblings get along very nicely, lined up in rows eating one leaf when they're little, spreading out so each one can gobble a leaf of its own as they grow bigger. In captivity, especially if they don't find good fresh leaves to eat, they become confused and can start to "bite and devour one another." The best way to rear these butterflies is to protect their host plant outdoors and watch them grow up naturally.
Though toxic to most predators, philenor caterpillars have one unusual predator: ladybugs (ladybirds, ladybeetles). Ladybug larvae usually eat aphids but they can survive eating a small, young philenor caterpillar. According to https://mdc.mo.gov/discover-nature/field-guide/pipevine-swallowtail-blue-swallowtail, when larvae of these species meet, the beetle larva is likely to bite the caterpillar. The caterpillar can bite back in self-defense, although it's not known to eat beetle larvae. Which creepy-crawly will win the biting fight? Usually the one that is bigger at the time. Mature caterpillars are much bigger than ladybug larvae. Hatchling caterpillars are not.
People have, as Pedromariposa has, made video recordings of the caterpillars stripping leaves off these vines. This is one of the Swallowtail species that have enough sense not to eat their siblings; butterflies try to give each of the younger siblings in the brood a foodplant of its own, but some of the first few eggs may be placed in a group on one plant, producing restless but nonviolent family groups:
People have taken time-lapse photos of how the caterpillar achieves that funny-looking chrysalis...not quite as grotesque as some of the tropical Battus and Atrophaneura chrysalides, but still, it's a weird-looking process.
Chrysalides are usually pale brown, as in the video. But Tashawidow watched a philenor hirsuta caterpillar develop this bright green and yellow chrysalis in Redding, California, in May 2020:
Spillane found a brown and a green chrysalis side by side in Sausalito in January 2021...these caterpillars made little attempt to seek cover before entering the most vulnerable stage of their lives. (Both photos from Inaturalist.)
After eclosion (emergence from the chrysalis) the butterflies fly for up to two weeks. Art Shapiro, who ought to know, claims that they can live as long as a month after eclosion--but apparently few do, because everyone else says their adult lifespan is two weeks.
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