Month: October 2019

Striking contrasts of orange body and black spines may serve as a warning to predators to avoid making a meal of Gulf fritillary caterpillars.

This week Bug of the Week finds itself in the tidewater of Virginia and on the sunny shores of South Carolina, where brilliant members of the aster clan carpet the sands just leeward of the dunes. Here in the waning days of autumn a beautiful butterfly dressed in orange and black sips nectar in preparation for its journey to frost-free zones along the Gulf of Mexico, while others find romance along a footpath in a garden. The Gulf fritillary is a broad ranging species taking up permanent residence from Argentina to the southern United States. During summer, peregrinations take it as far north as San Francisco on the west coast and New Jersey on the east coast, but in autumn this vagabond travels south to the warm climes of the Floridian peninsula to spend the winter.  

Flowers of the passion vine are among the most magnificent in the plant world.

 Like other members of the longwing butterfly clan, larvae of this orange and black beauty consume leaves of passion fruit vine. The blossom of the passion fruit vine is one of the most gorgeous in the angiosperm world. Exotic flavors of the passion fruit are used around the world adding zest to ice cream, cheesecake, and mixed drinks. Passion fruit is rich in vitamin C and lycopene and consuming this delicacy is said to sooth a queasy stomach, according to Andean lore. As a group, passion fruit plants are protected from most leaf-munching caterpillars and other vegan insects by a veritable witch’s brew of highly toxic chemicals including alkaloids, a family of toxins that includes strychnine and nicotine, and cyanogenic glycosides, chemicals that release cyanide upon entering the digestive tract of a caterpillar or human.

The gorgeous Gulf fritillary butterfly harbors a couple of unpleasant surprises for any would-be predator.

However, the Gulf fritillary and other members of its clan, including the zebra longwing we met in a previous episode, turned the tables on passion fruit plants, bypassing the noxious defenses and feasting with impunity on their leaves. Some species of longwings sequester cyanogenic glycosides from their food and others manufacture these compounds on their own. presumably for defense. The striking orange and black coloration of the Gulf fritillary warns vertebrate predators not to mess with this beauty. In addition to any plant derived defenses, the gorgeous Gulf fritillary has one more bit of chemical trickery to help keep predators at bay. Glands on the abdomen produce and release a concoction of complex esters when the adult butterfly is disturbed. This stinky defensive fluid dissuades predators such as birds from making a meal of these dazzling butterflies.

Like its cousin the Gulf fritillary, a zebra longwing caterpillar consumes large quantities of passion vine leaves each day.

But the beautiful Gulf fritillary is not all about noxious chemicals and defense. Oh no, in the Norfolk Botanical Garden some Halloween romance was literally afoot, where a mating pair of butterflies engaged in a quixotic duet along a footpath. Many male butterflies, including Gulf fritillaries, have a clever trick for winning the affections of would-be mates. At the tip of his abdomen the male Gulf fritillary has small bristles called hair pencils. The male uses his hair pencils to distribute aphrodisiac pheromones on the antennae of a potential mate. Courtship pheromones are often released by the male over the female while both are in flight. These pheromones calm the female’s innate escape response, and upon landing the male may hover over the female dusting her with more pheromones. The resulting romantic swoon induced by the pheromone allows the male to approach his mate and, well, shall we say, fulfill the biological imperative of procreation.

Asters provide a rich source of carbohydrates to fuel the Gulf fritillary’s autumn migration to frost-free zones in the Deep South along the Gulf of Mexico. Along a foot path a male Gulf fritillary releases aphrodisiac pheromones over the antennae of a potential mate. Will this clever behavioral trick result in a Halloween treat?

 Beautiful, dangerous, romantic; what could be more perfect for an insect dressed in orange and black for this festive autumn season? Hope you have a Happy Halloween!     

Acknowledgements

 References used in the preparation of this Bug of the Week include ‘Caterpillars of Eastern North America’ by David L. Wagner; ‘Coevolution of Animals and Plants’ by Lawrence Gilbert and Peter Raven; ‘Gulf Fritillary Butterfly, Agraulis vanillae (Linnaeus) (Insecta: Lepidoptera: Nymphalidae)’ by Jaret C. Daniels; ‘Novel chemistry of abdominal defensive glands of nymphalid butterfly Agraulis vanillae’by Gary N. Ross,Henry M. Fales, Helen A. Lloyd, Tappey Jones, Edward A. Sokoloski, Kimberly Marshall-Batty, and Murray S. Blum; and ‘Introduction to General and Applied Entomology, Third Edition’ by V.B. Awasthi. We thank the amazing arborists of Trees South Carolina and the Norfolk Botanical Garden for providing the inspiration for this Bug of the Week.

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Color and pattern of the gorgeous pipevine swallowtail warn predators of a nasty meal should they dare to attack. Image credit: Dr. Paula M. Shrewsbury

In recent years Bug of the Week has visited several beautiful butterflies whose dominant wing coloration is based on the theme of a black background with series of patches and spots in shades of white, orange, and blue. Butterflies participating in this cabal include the dark female form of the eastern tiger swallowtail, the pretty red-spotted purple, the eastern black swallowtail –eater of parsley and dill – and the clever spice bush swallowtail, whose larvae mimic serpents. Why have all of these beauties converged on a relatively common color scheme? 

Dutchman’s pipe is a favored host for Polydamas caterpillars. Eggs deposited on a growing tip will later hatch into very hungry caterpillars.

Caterpillars of the butterflies that we meet today, the pipevine swallowtail and the Polydamas swallowtail, dine on plants in the birthwort family, Aristolochiaceae, that include vines commonly known as pipevines. Members of this family produce a class of compounds known as aristolochic acids which are known to be mutagenic, carcinogenic, and toxic to kidneys of mammals. As they consume leaves of pipevine, these swallowtail caterpillars store these toxins and in turn pass them along to the adult butterflies and also to their eggs. Aristolochic acids sequestered by caterpillars may help protect them from attack by parasitic wasps. Adult butterflies are rendered distasteful to vertebrate predators such as birds by virtue of these noxious compounds. It is believed that birds attempting to eat butterflies whose larvae consumed pipevines have a nasty experience that teaches them not to mess with darkly colored butterflies. Other species of butterflies capitalized on the lesson taught by the pipevine and Polydamas butterflies by evolving color patterns to mimic their appearance, thereby gaining protection from visually astute predators. This type of mimicry, in which warning colors of a distasteful species like these swallowtails act as a model copied by other palatable butterflies, is called Batesian mimicry. The great English naturalist Henry Bates first described this form of mimicry while studying butterflies in Brazilian rainforests.

This gorgeous resting pipevine swallowtail will soon seek pipevines on which to deposit brightly colored orange eggs that hatch into tiny caterpillars. As the caterpillars feed and grow, they accumulate noxious compounds and take on a startling visage, complete with fleshy dangling appendages and orange bumps advertising their distastefulness.  Video credit: Dr. P. M. Shrewsbury

We met other species of Batesian mimics, such as harmless flower flies that mimic stinging bees and stilt-legged flies that mimic wasps. And adult butterflies are not the only creatures that mimic pipevine swallowtails. Recall that the caterpillars of these swallowtails are also laced with aristolochic acids. Scientists believe that a cyanide producing millipede with deep red coloration mimics the color and pattern of the pipevine caterpillar, thereby gaining protection from predators. We have also seen this mimicry before with several orange and black insects that eat milkweed, including monarch caterpillars, milkweed bugs, and milkweed tussock moth caterpillars.  This convergence on a similar, easily recognizable color pattern by two or more nasty-tasting insects is called Müllerian mimicry, named for the famous German naturalist Fritz Müller.

As this spectacular butterfly season comes to an end, try to grab one last glimpse of one of these dark winged beauties and ponder the question – model or mimic?

Acknowledgements

Bug of the Week thanks observant Dr. Shrewsbury for spotting adults and larvae of the pipevine swallowtail and providing the image and a video featured in this episode. “Secret weapons” by Thomas Eisner, Maria Eisner, and Melody Siegler, and the Featured Creature articles “Common name: pipevine swallowtail, blue swallowtail scientific name: Battus philenor (Linnaeus 1771) (Insecta: Lepidoptera: Papilionidae: Papilioninae: Troidini)” and “Common name: Polydamas swallowtail, gold rim swallowtail, tailless swallowtail scientific name: Battus polydamas lucayus (Rothschild & Jordan) (Insecta: Lepidoptera: Papilionidae: Papilioninae: Troidini)” by Donald Hall provided valuable insights into the clever ways of this week’s stars.

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A gorgeous Carolina mantid waits for a meal – or perhaps a mate who might be a dinner “guest”.

What a year this has been for insects in general, with banner populations of butterflies, moths, stink bugs, and many others. Not surprisingly, when populations of plant-eaters flourish, we often see an upswing in consumers higher up in the food chain. In previous episodes, we met the two amazing and beautiful foreigners that sit atop the invertebrate food webs in our landscapes, the European mantis, Mantis religiosa, and the Chinese mantid, Tenodera sinensis. This week we visit one of our native mantids, the Carolina mantid, that is turning up in record numbers in our area.  

The Carolina mantid ranges from the Canadian border into Mexico and from the east coast to Nevada and Arizona. Like other mantid species, Carolina mantids eat a wide variety of insects and spiders found in gardens and landscapes. And yes, on occasion the female consumes her unfortunate mate, especially so when mantids are raised in captivity. The extent to which this is an artifact of being raised under unnatural conditions is not known, but it is reported that well-fed gals are less likely to consume their suitors than hungry ones. Several of the mantids I have seen over the past week are gravid females, those carrying a full load of eggs. When enough prey has filled her belly and a lucky, or perhaps unlucky, male has contributed his sperm, the female will deposit her eggs in an egg case. The entomological term for the egg case is ootheca. A mantid’s ootheca is composed of frothy material called spumaline that has the look and feel of an elongated glob of Styrofoam. The female mantid secretes spumaline from glands in her abdomen as she deposits eggs, usually on vegetation or on structures such as fences and houses. The ootheca serves as a protective matrix for scores of tiny eggs resting within.

From afar, a very pregnant female Carolina mantid seems to have her sights set for incoming prey. As the camera invades her personal space, she gives the paparazzi the kind of “what are you looking at” stare that only a mantid can deliver. This disdain for bug geeks apparently starts early. Even juvenile Carolina mantids would rather groom their raptorial forelegs than indulge a guy with a camera. However, the arrival of a large carpenter bee can trigger a hasty retreat.

After emerging from the ootheca, tiny hatchlings take their first glimpse of a world full of wonderful morsels to eat and fearsome predators to be eaten by.

After surviving the chill of winter, eggs complete their development with the return of warm weather. Warm weather signals the return of foliage to plants and the presence of legions of small tasty insects that serve as food for developing mantids. Sometimes mantids will deposit eggs on vegetation that could find its way into a home, such as on a Christmas tree or pine garland. In the warmth of a home, eggs within the ootheca may develop and hatch, and become an extra special holiday surprise. With the holiday season not far away, perhaps it is time to make a mental note to inspect boughs and trees before they enter a home. 

Although egg cases of praying mantids can be purchased commercially and placed in the garden, the effectiveness of mantids as biological control agents is ambiguous at best. Remember, they are generalist predators and may capture and eat beneficial insects as well as pests, not to mention each other. Nonetheless, mantids are fascinating to observe and study and I always have an ootheca in my landscape to restock my garden with these marvelous creatures when spring returns. 

Acknowledgements 

Bug of the Week thanks Kathleen, the crew at MPT, and the staff and students at the Howard Conservancy for providing the inspiration for this episode.

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On a dewy morning, male (left) and female (right) carpenter bees await a warm-up from the brilliant autumn sun.

You may have seen the carpenter bee’s hole on the outside of your siding – here’s a look at the brood galleries on the inside.

In this season of record breaking, smoking hot days, blossoms have been humming with a multitude of bees, butterflies, and other fascinating pollinators. Visits to flower beds and pollinator gardens with children and adults during the past week or two, sparked wonder at the vast number of large bumble bees busily gathering nectar from late season blossoms. While there is no doubt that many of the bee sightings were indeed bumble bees, this is the season that a fresh crop of carpenter bees mobs patches of flowers to fatten-up on floral delights in preparation for the upcoming winter. Months ago busy female carpenter bees devoted weeks constructing galleries in wood, provisioning these galleries with pollen, and depositing eggs within. Summer and early fall were a time for the eggs to hatch and the young bee larvae to consume these morsels, complete their development, pupate, and emerge as adults.  Galleries used as nurseries throughout spring and summer will soon serve as winter refuges for this year’s class of carpenter bees.

Note the shiny hairless abdomen of the carpenter bee.

With a little practice, carpenter bees can be distinguished from their look-alike bumble bee cousins. A carpenter bee’s rump is relatively naked, whereas a bumble bee’s rear end is usually quite well cloaked with hair. The head of the carpenter bee is about the width of the thorax, the body segment just behind the head. The head of a bumble bee is noticeably smaller than thorax.

Hair on the abdomen is a hallmark of the bumble bee.

Having identified the bee as a carpenter bee, how does one distinguish the guys from the gals? The gender of some carpenter bees, such as the Large Carpenter bee, Xylocopa virginica, are easily recognized by the presence or absence of a large creamy white patch just below the antennae on the front of its face: the male sports the white patch, but the face of the female large carpenter bee is entirely black. On occasion I have captured large male carpenter bees with my hand to demonstrate that they are not to be feared, as they have no stinger – only female bees are equipped with this notable appendage. On one occasion I mistakenly grabbed a female carpenter bee and learned the awesome power of this appendage. If for some strange reason you choose to handle large carpenter bees, please be certain that they are indeed carpenter bees and not bumble bees, and only handle the he bee and not the she bee.

Bumble bees have a hairy abdomen, carpenter bees do not. The male carpenter bee has a white patch on his face and the female’s face is entirely black. A male foraged on a lower blossom until he spotted a female foraging just above, and then both appeared to have other business on their minds as they raced away.

Another observation regarding behaviors of carpenter bees and bumble bees comes at the close of the work day. Industrious bumble bee workers usually return to their nest at dusk with the final loads of nectar and pollen to fatten-up any future queens and drones that might still be developing in the nest. But unlike bumble bees, with the approach of nightfall large carpenter bees often remain behind on blossoms to snooze. With no nest to provision or hungry future royals to feed, it is no surprise to find sleepy carpenters resting on flowers in the early light of dewy autumn mornings. One of their favorite resting spots in my garden is a patch of catmint. Members of the mint family are renowned for their ability to attract a variety of pollinating insects, in addition to their medicinal qualities. Perhaps, the lazy behavior of my carpenter bees is related not only to the nighttime chill that cools their bodies, but also to some soporific chemical found in the nectar of mint. Who knows?

When the killing frost finally puts an end to my autumn bloomers, the last of the carpenter bees will enter their vacated brood galleries, not to return until next spring. On a cool autumn morning, take an early trip to the garden to visit the newly minted class of 2019 carpenter bees. 

Acknowledgements

Bug of the Week thanks MPT, University of Maryland Master Gardeners, and the Howard Conservancy for providing the inspiration for this episode. The really cool bee book “The Bees in Your Backyard: A Guide to North America’s Bees” by J. S. Wilson and O.M. Carril was used as a resource for this episode.

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