Month: December 2021

 

 

As the often-dreary days winter set in, you may be missing the antics and beauty of insects here in the DMV. Let’s take a quick trip to warmer climes to visit some gorgeous butterflies, longwinged heliconiids. Let’s head to Florida where several heliconiids reside or visit. 

First on the list is the remarkable Zebra Longwinged butterfly, Heliconius charitonia. These beauties live up to six months. Zebras and their kin evolved an interesting strategy to gather nutritious pollen used to sustain their unusual longevity. Zebras fly a well-defined route through the forest visiting trusty plants presenting fresh pollen-laden blossoms each day. This fixed-route behavior is called traplining and is employed by many tropical pollinators including bees, hummingbirds, and bats. After collecting a gob of pollen on its long, coiled proboscis, the butterfly secretes specialized enzymes to release the amino acids and other nutrients in the pollen. Nutrients absorbed through the membranes lining the proboscis are used to produce eggs and maintain the high level of activity required to zoom about the forest. 

In addition to visiting flowers laden with pollen, the Zebra also searches for different species of plants in the passion vine genus, Passiflora. These tropical vines bear the magnificent passion flower. Several species of passion vine are used by the immature stages of the zebra and other heliconiid butterflies as a source of food. These larvae are voracious caterpillars and consume great quantities of leafy tissue on a daily basis. 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. 

However, members of the heliconiid clan, including the zebra longwing and the gorgeous Gulf Fritillary, turn the tables on passion fruit plants, bypassing the noxious defenses, and feasting with impunity on their leaves. Some 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 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. 

This very hungry caterpillar turns into the beautiful Zebra Longwing, with banded wing patterns resembling those of a zebra. In the Amazon Basin you might see the stunning Sara Longwing with striking white chevrons on its iridescent blue-black wings. In Central America and the southern tier of the United States, brilliant orange, black, and white Gulf Fritillaries sip nectar and collect pollen from a variety of plants.

With so much leaf-munching by the larvae of heliconiids, one wonders how the vines of Passiflora survive. It seems that the mobile and eagle-eyed butterflies locate passion-vine plants by the shape of their leaves. To fool these clever herbivores, tropical passion-vines have evolved leaves that vary dramatically in shape. In this way it is more difficult for butterflies to zero in on any one leaf shape as they search for food for their young. At least one species of Passiflora has taken this game of deception one step further. It has evolved a small structure on the tips of its leaves resembling the egg of a Heliconius butterfly. Larvae of Heliconius are known to be cannibalistic and female butterflies may avoid placing eggs on a leaf if it is already occupied by another caterpillar or by an egg about to hatch. By creating a structure that resembles an egg, the passion-vine hangs a sign that says “no vacancy” to the female butterfly looking for a spot to lay eggs. This remarkable act of mimicry helps the passion vine escape the ravages of very hungry caterpillars. 

Bug of the Week wishes you Happy Holidays and a Joyous and Healthy New Year!

 

 

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; and “Novel chemistry of abdominal defensive glands of nymphalid butterfly Agraulis vanilla” by Gary N. Ross,  Henry M. Fales, Helen A. Lloyd, Tappey Jones, Edward A. Sokoloski, Kimberly Marshall-Batty, and Murray S. Blum; “Passiflora (Passifloraceae) defenses against Heliconius cydno (Nymphalidae: Heliconiinae) oviposition” by Kim Khuc and “Heliconius Homepage” https://www.heliconius.org/biology/ecology/

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This week we dive into the Bug of the Week mailbag to learn about some fantastic aphids discovered on limbs of a beautiful oak tree near the Chesapeake Bay.

‘Twas two weeks before Christmas and what did I see, But some giant bark aphids on a leafless shade tree. 

Aphids are not usually known for their very large size, But these babes on tree limbs win the “big-aphid” prize. 

As steadfast sap-suckers they spent several past weeks Sipping plant-sap from branches through stout hollow beaks. 

Aphid moms slurp sweet phloem by night and by day, And transform it to nymphs – born alive, by the way. 

These strange spawning efforts are quite something to see, Bug-geeks call this birth-trick viviparity.  

As autumn days wane and cold winds start to blow These gals change their game-plan. They just seem to know. 

No more birthing of youngsters on twigs in the cold, They lay eggs on tree branches, many thousand all told. 

Tiny black aphid eggs seem the perfect life stage To brave wicked winter when vicious storms rage. 

And if aphids can dream, their fond hope might just be That no hungry egg-eaters find their young on the tree. 

In this season of darkness of cold and of gloom Not far off is a season when trees start to bloom.

Cast off fear giant aphids, be glad and be happy! Next spring eggs will hatch when trees get all sappy. 

Through millions of years your plan has been true What more can be said? Happy holidays to you!

Braving icy winds and freezing temperatures, giant willow aphids try to squeeze in one more generation before Old Man Winter puts an end to their season.

Acknowledgements

 Bug of the Week extends apologies to Clement Clark Moore.  We also thank Dr. Catherine Carr for providing the inspiration and an image for this episode. Like woolly alder aphids, woolly beech aphids (aka beech blight aphids), and others we met in previous episodes, these aphids reproduce parthenogenetically, that is without males. To learn more about magnificent giant aphids on beech and willows, please visit the following websites:  

University of Florida Featured Creatures: giant bark aphid

InfluentialPoints.com: Tuberolachnus salignus, Giant willow aphid

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December 2021 will be remembered for many reasons, not the least of which is supply chain shortages that plague shoppers this holiday season. In addition to shortages of electronic devices and automobiles, choose-and-cut Christmas trees are somehow in short supply.  Ah, but my favorite trusty tree farm had no shortage of trees and, in what has become a regular event, my holiday tree had no shortage of spiders. This year my Nordmann fir had at least one tiny but very entertaining jumping spider.

Jumping spiders are unlike their cousins, the well-known orb weavers made famous by E. B. White in Charlotte’s Web. As their name implies, jumping spiders are hunters, relentlessly on the prowl for small insects and other spiders which they stalk, grab, subdue, and pulverize with powerful fangs. They are among the most intelligent of all arthropods. Their tiny brains are able to form spatial maps and plan circuitous routes to sneak up on unsuspecting prey. They are highly entertaining to watch as they explore their environment in search of prey. Their eight eyes, two of which are extraordinarily large, allow them to precisely track moving prey. Their mating rituals are spectacularly complex and rival those of vertebrates like Bower Birds. You can watch them hunt and court at this link: https://www.nationalgeographic.com/animals/article/160121-jumping-spiders-animals-science

After bringing a field-grown Christmas tree into the house, I found this little jumping spider touring my houseplants. Once the stare-down with the camera guy was finished, the spider continued its explorations. Watch how it takes a shortcut from one leaf to another at normal and one third speed, hence the name jumping spider!

Other spiders play important roles in the anthology of holiday trees and their decorations. Each year as we put the finishing touches on our holiday tree, a serious debate arises regarding the quantity of tinsel necessary to complete the task. Some years ago, I explored the murky origins of tinsel. To some, the silvery strands of unknown composition evoke images of glistening icicles or shimmering crystals of frost on evergreen branches. But how did tinsel become part of a holiday tradition in so many households? To aficionados of arachnids, the tradition of festive tinsel has several different origins. One Christian story tells of Mary’s harrowing escape from Roman soldiers as she and Jesus hid in the hills near Bethlehem. With Herod’s legion in hot pursuit, Mary entered a cave seeking refuge. Spiders quickly sealed the entrance with silk and when soldiers arrived and saw the undisturbed webs, they disregarded the cave as a hideaway and continued their search elsewhere. Often maligned spiders saved the day! Since that time, tinsel has been strung on Christmas trees to represent a glistening spider web and to commemorate the spider’s miraculous deed.

Other tinsel legends from Germany and the Ukraine tell of spiders escaping the lethal brooms of housekeepers by hiding in dark corners of the home during preparations for holiday celebrations.  After exiting their redoubts on Christmas Eve, spiders excitedly explored the evergreen trees that had been brought inside and then left behind glorious cloaks of gossamer webs. When Father Christmas arrived that night and saw the gray spider webs, he miraculously changed them into sparkling silver strands, much to the delight of families who viewed the trees on Christmas morning. Since that time, tinsel has been strung as a symbol of the remarkable event.

In the wild, jumping spiders prowl vegetation looking for prey and, apparently, amuse themselves by taking tiny bungee jumps from high places.

Many spiders survive winter’s chill as eggs protected in silken sacs. If the spider’s last haunt was a spruce or fir, then egg sacs may enter homes as stowaways on Christmas trees. In the warmth of holiday homes, eggs hatch and humans may be recipients of dozens of unexpected visitors. If you discover a spider egg sac on your Christmas tree or fresh evergreen boughs, simply pluck off a small piece of infested branch and place it and the egg sac outside on a shrub. This will allow the spiders to hatch just in time to deliver a deferred holiday gift of pest control in your garden. And as for my adorable jumping spider, well prey is scarce during winter months in my home. My spider was released on a hemlock where overwintering woolly adelgids may serve up a holiday treat for this clever hunter.

Acknowledgements

We thank the Maryland Christmas Tree Association for providing the inspiration for this episode. The fascinating article “The execution of planned detours by spider-eating predators” by Fiona R. Cross and Robert R. Jackson was used as a reference for this episode.

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