This Red-spotted Purple butterfly was my reward for tromping around outside, searching for creatures, on one of the hottest days of the hottest summer on record in North Carolina.
The temperature was in the high 90’s F, the air was heavy with humidity, and I was wandering around one of my favorite places – the grounds of the North Carolina Museum of Art. Few creatures were out and about, as most were sheltering from the ridiculous heat. But amateur nature bloggers are made from pretty stern stuff, and this was my last chance to spend extended time outdoors before the work week started again.
I had been out for about an hour with not much to show for my efforts, when I caught sight of a dark shape fluttering along the edge of some trees. I moved closer to get a better look, and all thoughts of retreating to a dark, air conditioned building fled from my mind.
This was one beautiful butterfly.
|Family||Nymphalidae (“brushfoots”) (subfamily Limenitidinae “admirals and relatives”)|
|Genus species||Limenitis arthemis astyanax|
Red-spotted Purple butterflies belong to the “brushfoot butterfly” family Nymphalidae, which contains more species worldwide than any other butterfly family. There are approximately 3000 brushfooted butterfly species worldwide, around 160 of which can be found living in, or visiting, North America (Pile, 2020).
Butterflies classified in this family have reduced front legs, which makes them appear to have only four legs at first glance. The front legs look like little brushes (thus the family name) and aren’t used for walking.
Eggs: Greenish-gray; laid one at a time on the tips of host plant leaves (Daniels, 2003).
Caterpillars: Long, thin, and knobbly, with a pair of long, bristly-looking horns on the thorax. Red-spotted Purple caterpillars are mottled gray, brown, tan, and white and closely resemble bird droppings, especially at rest. The pupal chrysalis also resembles bird droppings for camouflage from predators (Bartlett Wright, 1993).
Adults: Red-spotted Purples are large butterflies, with adults growing to 3.0-3.5inches (7.6-8.9cm) wingspans; both sexes look similar.
Their overall color is brownish-black, especially in direct sun. However, as with many butterflies, the scales that cover Red-spotted Purple wings reflect iridescence and this butterfly display beautiful blues and violets when sunlight strikes their wings at just the right angle.
The dorsal (“top”) surface of their wings flare with deep purplish-blue iridescence. Their hind wings reflect this beautiful color nearly to their base and have several rows of alternating purplish-blue and velvety black along the wing margins. Their forewings also appear bright blue near the margins but include a line of white spots along the outer margin as well as one of bright orange spots.
The ventral (“bottom”) wing surfaces are more dull-colored overall, without the iridescent sheen seen on the dorsal wing scales. But when Red-spotted Purple butterflies close their wings, you can see the bright reddish-orange spots that give them their common name.
Their legs, antennae, and mouthparts are velvety black, as are their bodies except for some bright white spots. Their black faces have white stripes running from top to bottom. Like all butterflies classified within the brushfoot butterfly family Nymphalidae, their forelegs are significantly shorter than the middle or hind legs.
Like all butterflies, Red-spotted Purples undergo “holometabolism”, which means they progress through four life stages: egg, larva, pupa, and adult. Each stage is entirely distinct, with different appearances and behaviors. In the case of butterflies, their larval form is called “caterpillar” and the pupal form develops in a special case called a “chrysalis”, which is unique to lepidopterans.
Red-spotted Purples can be found in North Carolina from the end of April to end of October. They hatch and develop into multiple generations per season (Daniels, 2003). Most of the time, they overwinter as chrysalises but during warmer winters, some individuals may survive as caterpillars and pupate in the early spring.
Habitat and Distribution
Red-spotted Purple butterflies are found across North Carolina but are fairly uncommon. They live in open woodlands and edge habitats. Males often perch in the sunshine and wait for females; when they fly, these butterflies alternate quick, fluttering wing beats alternated with long, flat-winged glides.
Food and Feeding Behavior
Larval Host Plants:
- Cherries (Prunus)
- Willows (Salix)
- Oaks (Quercus) (Opler, 1994)
- Poplars and aspens (Populus)
- Hawthornes (Crataegus)
- Apples (Malus)
Caterpillars eat only the veins of their host plant’s leaves. They feed from the tip of the leaf and follow the vein about halfway down the leaf, then rest on the end of the vein (Daniels, 2003).
Adult Food Plants:
Adults will sometimes visit flowers but prefer to feed on tree sap, carrion, dung, and especially rotting fruit (Daniels, 2003).
- Red-spotted Purple butterflies are not poisonous but their coloration looks similar to another North Carolina butterfly species, the Pipevine Swallowtail (Battus philenor). Mimicking a noxious species that predators learn to avoid gives Red-spotted Purple butterflies “protection by association” from predators, which is referred to as “Batesian mimicry”.
- Red-spotted Purple butterflies can be distinguished from Pipevine Swallowtails by the lack of “tails” on the margin of the hind wings and the presence of red-orange spots on the ventral wing surfaces near the body.
- Red-spotted Purple butterflies are actually the same species as another butterfly called the White Admiral (Bartlett Wright, 1993).
- White Admirals are found in the northern part of the country, while Red-spotted Purples are the southern form, as they prefer warmer temperatures and lower elevations.
- Despite being the same species technically, these butterflies look very different. White Admirals reflect less blue-purple from the dorsal surface of their wings and a wide white band runs up through the center of the wings.
Bartlett Wright, Amy. 1993. Peterson First Guides: Caterpillars. Boston, MA: Houghton Mifflin Company.
Daniels, Jaret C. 2003. Butterflies of the Carolinas. Cambridge, MN: Adventure Publications, Inc.
Glassberg, Jeffrey. 1999. Butterflies Through Binoculars: The East: A Field Guide to the Butterflies of Eastern North America. New York, NY. Oxford University Press.
Opler, Paul A. 1994. Peterson First Guide to Butterflies and Moths. Boston, MA: Houghton Mifflin Company.
Pyle, Robert Michael. 2020. National Audubon Society Field Guide to Butterflies: North America. New York, NY. Alfred A. Knopf.
Wagner, David L., 2005. Princeton Field Guides: Caterpillars of Eastern North America. Princeton, NJ: Princeton University Press.