Black Swallowtail

We tend to think of butterflies as symbolic of everything delicate and dainty, but not so the actual insect. The Black Swallowtail, Papilio polyxenes, a common species throughout the summer, is a prime example. At all life stages, this insect is the epitome of durability.

Male

I was prompted to write about this species by an encounter with a female Black Swallowtail at Sinton Pond Open Space here in Colorado Springs on June 5. She was flitting among a stand of Poison Hemlock, Conium maculatum. While this plant is, as the name implies, highly toxic to people, it is one of the host plants for the caterpillar of the Black Swallowtail. Indeed, many members of the parsley family are palatable to the larvae.

I somehow managed to capture the female in the act of ovipositing, then found the egg after she left. She determines the suitability of the plant by “tasting” it with her tarsal segments (feet), scratching the plant into liberating chemical compounds that the butterfly recognizes as a host plant.

The egg is a hard-shelled object impermeable to moisture loss, and insulating the embryonic larva within from the elements. The caterpillar chews its way out of the egg in about 4-9 days, consuming the empty shell so as to leave no trace for birds and other predators to clue in on. It then turns its attention to munching on the host plant.

When they are small, Black Swallowtail larvae mimic bird droppings in color and texture, being black with a white “saddle” marking. It is easy to dismiss the little caterpillar as an inanimate object on the dill, fennel, parsley, or carrot plants in your garden. That white mark is an expression of uric acid deposits in the cuticle of the larva, which may act as antioxidants in disarming the phototoxic chemicals that its host plants use in their own defense.

After three molts, the larva suddenly becomes a dapper, zebra-striped animal that is hard to miss, especially considering the caterpillars get pretty large and are generally feeding on plants that have very slender foliage.

At this point, the Black Swallowtail caterpillar has a number of defenses at its disposal for thwarting predators. First, it uses its jaws to hurl its fecal pellets, thereby eliminating trace evidence (and aromatic clues) of its presence. Should it be directly antagonized, it will evert a gland called an osmeterium from a fold in the thorax. This gland is bright orange and resembles the forked tongue of a reptile. Further, the gland exudes a substance that effectively repels ants and potentially other insect predators, especially if the fluid can be smeared directly on an attacker. One of the components of this awful cocktail is isobutyric acid. That’s right, it smells like rancid butter.

The larval stage can last anywhere from 10-30 days, after which the caterpillar molts for a fifth time, into the pupa stage.

When preparing to enter the pupa stage, the caterpillar spins a silken “safety belt” around itself, such that it is leaning back off the stem, twig, or other surface to which it is anchored at the rear by a button of silk and hooklike appendages on the tip of its abdomen. The chrysalis looks more like a shard of dead wood or other plant material than anything animal, and is easily overlooked. The pupa is the overwintering stage for the Black Swallowtail, but in summer generations, this stage lasts from 9-18 days.

Adult male butterflies emerge two or three days ahead of females, and they immediately try to establish a territory. This is often at the summit of a ridge or butte, and this behavior is known as “hilltopping.”. Competition is keen, however, and males will engage in aerial combat for possession of prime real estate. They collide violently enough to be audible to human observers, if the butterflies don’t chase you off, too.

The butterflies quickly become battered, their “tails” lost on the wind, but the wear on their wings hardly slows them down.

Females ascend the peaks where they are intercepted by the males. Once mated, a female begins the life cycle anew. Females are much darker than the males, and mimic the distasteful Pipevine Swallowtail where the range of both species overlap.

The Black Swallowtail ranges throughout North America east of the Rocky Mountains, and in Arizona and southern California as well. Northerly populations have up to two generations annually, with at least three generations in the south. You can almost be guaranteed to see them simply by planting carrots, parsnips, celery, fennel, dill, or any related herb/vegetable in your garden.

Female

Sources: Berenbaum, May R. 1989. Ninety-nine Gnats, Nits, and Nibblers. Urbana: University of Illinois Press. 263 pp.
Hall, Donald W. 2011. “Eastern Black Swallowtail,” Featured Creatures. Entomology and Nematology Department, University of Florida. EENY-504.

Moth Monday: Sophora Worm

One of the challenges I enjoy is matching caterpillars to their adult moths, and vice versa. Usually one of the two is spectacular and obvious, and the other is cryptic and/or scarce. Such was the case when I encountered the larvae known as the Sophora Worm, Uresiphita reversalis, of the family Crambidae.

I found many of the caterpillars amid their silken webbing on a common ornamental shrub in Tucson, Arizona on May 20, 2010. Turns out the plant was Texas Mountain Laurel, Sophora secundiflora, easily identified by its large, purple flowers and resulting robust pea-like pods. This is a native host for the moth, but the caterpillars are also known to eat non-native “broom” plants such as French Broom (Genista monspessulana), and other Genista species. This habit has given rise to an alternate name for the Sophora Worm: “Genista Broom Moth.”

Additional host plants include lupines (Lupinus), acacia (Acacia), false indigo (Baptisia), and other leguminous plants. It is also reported from Crapemyrtle (Lagerstroemia indica) and honeysuckle (Lonicera), but these are probably incidental.

The caterpillars feed out in the open, in groups, and during the day, in stark contrast to most caterpillars that are solitary and nocturnal, the better to avoid potential predators. The bold colors suggest that Uresiphita reversalis is distasteful to their enemies, and indeed they accumulate the toxins of their host plants for use in their own self-defense. They sequester the quinolizidine alkaloids found in their leguminous host plants, incorporating the chemicals into their exoskeleton. Even so, damsel bugs and other predatory insects with piercing-sucking mouthparts simply bypass this external defense by puncturing the cuticle and feeding on the internal tissues of the caterpillars (Bernays and Montllor, 1989).

The length of the life cycle of this species varies considerably depending on season and latitude. It can be as short as five weeks from egg to adult under optimal summer conditions in southern climes, and as long as 25 weeks in winter in the more northerly reaches of its range. There may be four or five generations annually. In Berkeley, California there are two major flight periods, one from March to May and the other from July to October. Overwintering usually occurs in the pupal stage, but adults are sometimes found during this season as well.

Eggs are laid in clusters (averaging about 19 per clutch in the lab) on the upper- or underside of leaves. The larvae go through five instars (an instar is the interval between molts). Pupation occurs inside an opaque, white cocoon woven amid dense webbing.

The adult moth has a wingspan of 27-34 millimeters. They are seen most often during the day and are easily startled from their resting place. The body and legs of the moth are bright white. The hind wings, usually not visible when the insect is at rest, are bright yellow or orange.

One reference asserts that the Sophora Worm is native to Mexico and the southwest U.S. and has spread with its hosts up the coast of California to the Bay area; and also north and east to the Great Lakes and mid-Atlantic states, even Maine and Nova Scotia. It became established in Los Angeles in 1930, spreading rapidly from there. By the 1980s it was spreading through the San Joaquin and Sacramento Valleys (Powell and Opler, 2009).

I didn’t find an adult moth until more than a year later. The specimen imaged here was in the same neighborhood where I found the caterpillars, on June 11, 2011.

Note that this moth was formerly classified in the family Pyralidae, and is often still placed there incorrectly on several internet resources. It is currently in the family Crambidae, subfamily Pyraustinae.

Sources: Bernays, E.A. and C.B. Montllor. 1989. “Aposematism of Uresiphita reversalis Larvae (Pyralidae),” J. Lep. Soc. 43(4): 261-273.
Leen, Rosemary. 1995. “Biology of Uresiphita reversalis (Guenée) and Comparison With U. polygonalis maorialis (Felder) (Crambidae),” J. Lep. Soc. 49(2): 163-170.
Powell, Jerry A. and Paul A. Opler. 2009. Moths of Western North America. Berkeley: University of California Press. 369 pp.

Time to Delete "Moth" From Our Vocabulary

I recently learned of a controversial theory of metamorphosis that got me thinking about moths and butterflies. More on that later. Perhaps National Moth Week also had something to do with my thought process, and/or a Facebook post by a friend purporting a difference between moths and butterflies. Folks, there is no such thing as a difference between moths and butterflies.

There is no difference between moths and butterflies that does not have exceptions:

• Moths have feathery antennae. This is a myth. A few do, the males’ more “feathery” than the females’, the better to detect her pheromones wafting on the winds. Most moths have filamentous (hair-like) antennae.
  
• Moths are active at night. Hogwash. Most species are nocturnal, but there are plenty that fly during the day. Many fly both day and night. There are some butterflies that are nocturnal for that matter. I have personally seen some hairstreak butterflies attracted to lights at night.
  
• Moth caterpillars spin cocoons. Hardly any moth caterpillars spin cocoons, actually. Most simply have a naked pupa (the term “chrysalis” could also apply), often underground, sometimes inside a gallery the caterpillar bored in dead wood or living stem, stalk, or root. A cocoon does help insulate a pupa in exposed situations during weather extremes, so some species add this silken covering.
  
• Moths eat clothing. There is so much wrong with that statement I’m not sure where to begin. The larvae (caterpillars) of some moths do consume dried animal products like wool garments and blankets, but they are in an extreme minority. The feeding habits of the vast majority of moth caterpillars are of no consequence to people whatsoever.

It is that last item that hints at the real reason we insist on an artificial distinction between moths and butterflies. We need a villain, and the moth is it. Butterflies can do no wrong! They are colorful and carefree and their larvae eat weeds we don’t like. Moths are evil, their caterpillars consuming our crops and ravaging our forests. Moths are black, brown, or gray, and hide themselves in shame by day, only daring to emerge under the cloak of darkness that is night.

Moth Week may have started to peck away a little at the mythology of moths, but we should consider banishing the term “moth” from our lexicon altogether. Science recognizes that weevils, “ladybugs,” and “fireflies” are all types of beetles. Mosquitoes, gnats, and no-see-ums are acknowledged as types of flies. Moths are butterflies, by virtue of the fact that they are in the same order: Lepidoptera.

The theory of metamorphosis that made it onto National Public Radio implies that it isn’t butterflies and moths that are different, but the adult stage and the caterpillar stage. So different are they that perhaps they are separate species merged into one being. The caterpillar leads an entirely different lifestyle than the adult, and “dies” during the pupal stage, only to be “resurrected” as a new, winged creature at the conclusion of the life cycle. Yes, the majority of the scientific community scoffs at this idea, perhaps rightly so, but one can argue that the similarities between adult butterflies and moths are much smaller than the differences between the larva and adult of any one species.

Moths need positive attention for many, many reasons:

• Scores of moth species are endangered, or have populations that truly border on unsustainable. Contrast that with the “sky is falling” cries from butterfly conservationists every time there is the slightest slump in populations of hibernating Monarch butterflies.
  
• Moths are true pollinators, while butterflies (and many moths, to be fair) are merely “flower visitors.” Female yucca moths (family Prodoxidae) intentionally stuff a wad of pollen into the stigma of the host plant, thereby fertilizing it. The moth does this because her caterpillars require viable yucca seeds on which to feed. The caterpillars rarely consume the entire seed set, and both host and herbivore prosper. Several tropical orchid species rely solely on certain sphinx moths for pollination.
  
• Moths are incredibly important to the food chain. Countless birds, bats, even grizzly bears, rely on moths as a food source. Oh, add fish, reptiles, amphibians, spiders, and other insects to that list. Many of those predators are in fact moth specialists. Some spiders even mimic the pheromones of certain female moths to attract the male moths to their webs.

It is time to call “moths” what they really are: butterflies. Time to stop discriminating based on assumptions, myths, and preconceived notions of what moths should be. Reality is far more subtle, and nature lacks the anthrocentric lens we view Her through. Our vocabulary should reflect that reality, and not our prejudice, cynicism, and biases. Who is with me?

Winter 'pillars

Walking the dog the other day (February 26, 2012), I happened upon a small caterpillar slowly crossing the sidewalk in my Colorado Springs neighborhood. It was not a cold day, but not that warm, either. The high for the day was 46 Fahrenheit. Oh, they are out today, too (current temp 49 F at 3:50 PM). Looking more closely, I discovered there were dozens of other caterpillars, all roaming seemingly aimlessly.

The stretch of sidewalk passed along the edge of a large, open field, so that offered some clues as to what the caterpillars might be. I suspected they were “cutworms” of some kind because I knew that these owlet moths (family Noctuidae) overwinter as larvae. What surprised me was that the caterpillars were clearly not mature. They were of varying sizes, but still not big enough to be on the verge of pupating.

A little bit of internet digging (“Googling”), quickly produced the most obvious suspect: the Army Cutworm, Euxoa auxiliaries. I also recognized the adult moth as something I had seen under the eave of my apartment building last October (see image below). This common “miller” moth of the western U.S. is an overwhelmingly abundant, but its life cycle is quite unique.

Colorado Springs is very much a military town, so it seems appropriate that the “Army Cutworm” is so common here. Fortunately, the roving bands of caterpillars are not armed with anything more menacing than their tiny mandibles. Not that they cannot do widespread damage anyway. They don’t call them “cutworms” for nothing. The young caterpillars chew through the stems of young, tender plants. They can also eat slow-growing plants right down to the soil. Generalist feeders, the larvae find nearly any vegetation fair game. This species is a notorious pest of virtually every field crop from alfalfa (below) and wheat to barley, oats, potato, and sugarbeets. Cereal grasses are especially vulnerable, but damage is often spotty in a given field. They seem to prefer broad-leaved weeds otherwise, nibbling on the edges of leaves or chewing holes right through them.

Ironically, while the caterpillars surface and stroll on sunny winter days, they feed mostly at night and on overcast days in the fall and spring. When disturbed they coil into a tight “C” shape until danger passes.

Thankfully, the Army Cutworm is not without its enemies. Chief among them are parasitic wasps. Research has shown that the braconid wasps Meteorus leviventris, and Apanteles griffin are among the parasites of caterpillars in Oklahoma alfalfa fields(Soteres, et al., 1984).

Many of the adult moths, which emerge in late spring and early summer, escape the scorching midsummer heat by migrating to high elevations. There in the mountains they aestivate, gathering by the thousands under boulders in rockslides, or even inside mountain cabins. They do venture out at night to sip flower nectar. Amazingly, they are a critical portion in the diet of Grizzly Bears in parts of Montana and Wyoming, at times when other food is scarce. The insects are loaded with fat and protein and the bears merely turn over rocks and lick them off.

The moths are capable of incredible endurance; and they are not completely without defense. Laboratory experiments involving tethered moths fed with sugar water showed many individuals capable of flying more than 50 miles at a time. One flew for 23 hours at a nearly constant speed of 5.8 miles per hour, achieving the equivalent of 133 miles. They can hear approaching bats with the aid of a tympanic organ in the thorax, taking appropriate evasive action to avoid predation by these flying mammals. Resting moths, when disturbed, spray a liquid substance from the rectum that probably startles a potential predator, allowing the moth to take flight (Eisner & Eisner, 1992).

Moths that survive the bears and other predators return to the lowland plains to reproduce, females laying eggs in late summer and early autumn. Eggs are deposited on bare soil, especially in cultivated or overgrazed conditions. Hatching of the eggs is triggered by rains.

The Army Cutworm ranges from the Northwest Territories and Alberta south through Washington, Oregon, and Montana to Mexico, east to Minnesota, Nebraska, and Oklahoma. Scattered records include northern Michigan, Indiana, Missouri, Texas, and Florida. Their abundance can vary greatly from year to year depending mostly on weather (Cranshaw, 2011).

I am looking forward to seeing whether my neighborhood crop of caterpillars will translate into a bumper year for adult moths this spring. I would like to see a diversity of species at my porch light, however.

Sources: Brewer, Michael J. 1995. “Army Cutworm,” Department of Renewable Resources, University of Wyoming, B-1013.8.
Cranshaw, Whitney. 2011. “Miller Moths,” Colorado State University Extension, no. 5.597
Eisner, Thomas and Maria. 1992. “Euxoa auxiliaries: A Moth That Sprays,” Psyche 99: 3-14.
”Army Cutworm, Euxoa auxiliaries,” Digital Diagnostics, Oklahoma State University Entomology and Plant Pathology
”Species Page - Euxoa auxiliaries,” Entomology Collection, University of Alberta E. H. Strickland Entomological Museum
Powell, Jerry A. and Paul A. Opler. 2009. Moths of Western North America. Berkeley: University of California Press. 369 pp.
Soteres, K. M., R.C. Berberet, and R. W. McNew. 1984. “Parasites of Larval Euxoa auxiliaries (Grote) and Peridroma sausia (Hubner) (Lepidoptera: Noctuidae) in Alfalfa Fields in Oklahoma,” J. Kans. Entomol. Soc. 57(1): 63-68.

Carpet Cocoon

One day after I discovered the ”Carpet Caterpillar,” I discovered the remains of its cocoon in my living room carpet. This also explains why the caterpillar was so lethargic when I found it: a great amount of energy is expended in preparing to pupate.

Actually, there were the remains of two cocoons. Since I did not find another caterpillar, I suspect that I disrupted the one animal on two occasions. I was using boxes that had been in that spot for ages, and the caterpillar, once exposed, probably sought refuge under another box that I also eventually used.

You can even see the “trail” between the two pupal cells, a tiny trough in the carpet. Whether this represents actual damage to the fibers I have yet to find out (hey, I’m blogging, not vacuuming).

Carpet Caterpillar

At this time of year, even here in southern Arizona, I am always a bit surprised to find insect activity. Imagine my shock then at finding a caterpillar on my living room floor today. It was a familiar species, but still a bit early I think.

Tucson is landscaped with a plethora of ornamental fan palms, and it is from these trees that my caterpillar came. Known as the “palm flower moth” or “palm budworm,” depending on its life stage, Litoprosopus coachella is a frequent home invader in urban areas.

The mature caterpillars (roughly 25 millimeters in length) crawl off the tree to find a suitable place to spin a cocoon, and this sometimes takes them indoors. High winds will also dislodge them by peeling bracts off the trunk of the tree and sending them flying across the yard and against buildings. Any attached caterpillars will fly away with those botanical missles.

Despite their abundance, and appetite for the blooms of their host plant, the caterpillars are generally considered more of a nuisance than a bona fide pest. They may do minor damage to carpets once they get indoors and chew off fibers to incorporate into their silken cocoon.

The caterpillars are not terribly attractive, being a dusty greenish or pinkish color, devoid of much hair, and can be mistaken for a beetle grub at first glance. Look at the head. The two tiny spots near the corner of its mouth are one set of eyes. Most caterpillars are nearly blind, though, relying on tactile and chemical cues to navigate their world.

The remainder of the head capsule, that round, hardened area at the front, is filled mostly with muscles to operate the jaws. What jaws they are, too! The first time I found one of these, I made the mistake of trying to simply pick it up. I got a nasty nip out of it, and my reflexes sent the poor creature flying across the room. Ouch! Gila woodpeckers and northern mockingbirds are not as easily dissuaded as I, and feed heavily on these larvae.

Unfortunately, this insect does not redeem its appearance much through metamorphosis. The adult moth is equally dull and drab. Well, I suppose beggars (for signs of spring and the company of other animals) can’t be choosers, at least not in February.