Month: June 2021

Last week scorching temperatures in our region provided an excellent reason to head for the hills for a cool hike. Forest trails of the Catoctin Mountain Park provide both the perfect location to escape summer’s heat and an opportunity to visit some of Mother Nature’s most interesting recyclers of organic compounds, millipedes. Millipedes are detritivores, creatures that consume organic matter including mosses, algae, and decaying vegetation that carpet the forest floor. Millipedes belong to the subphylum of the arthropods called Myriapoda, those with “many feet.” Do they really have a thousand feet? Nah, they don’t really have feet, but they do have legs and the record number of legs for a millipede is somewhere around 750. However, most millipedes have fewer than 400 legs. Young millipedes have only a few body segments, each of which bears a single pair of legs. As millipedes molt and grow, body segments with two pairs of legs each are added. Millipedes live two to seven years and can produce hundreds of offspring during their lifetime. Millipedes do not bite or sting, but several species secrete noxious chemicals from glands lining the margins of their body.  

On a stony forest trail, we happened upon two remarkable members of the millipede clan. The first was Narceus americanus-annularis, one of the true giants of the millipede world in North America. Its otherwise dull brown body was accented with beet-red legs and red bands encircling the body at each segment. These colors might serve as a warning of noxious defenses ready to be unleashed by the millipede. Unable to resist handling Narceus earned me an acrid reward of benzoquinones, foul smelling droplets of the millipede’s chemical defense. A bit further down the trail, we encountered one of the flat-backed millipedes, perhaps Apheloria virginiensis. Blending in with the forest floor was clearly not this creature’s game as it sported lemon-yellow legs, alternating bands of yellow and black along the back, and pink-hewed margins.  

Many legs of the millipede work in a wavelike fashion to propel these timid grazers as they search for organic matter to eat. Watch as it munches moss on the surface of a boulder. Nearby, another millipede dashes across a forest trail. Bright contrasting colors may warn predators not to mess with these chemically defended detritivores. Defensive compounds released by this millipede smell like almond extract.

When plucked from the ground, the smell of almonds filled the air and brought me back to my days of organic chemistry when benzaldehyde was the unknown compound on the lab practical. Benzaldehyde is the compound found in bitter almonds and is used as a flavoring in almond extract. Ah, but benzaldehyde is not the only compound found in Apheloria’s defensive secretion. The other more lethal moiety released by the millipede is hydrogen cyanide, a highly toxic irritant. Glad no one sniffed this millipede too deeply! Millipedes, important recyclers of organic matter, are well-protected by potent toxins and irritants that could make a bird, lizard, or toad think twice about messing around with these denizens of the forest floor.

Acknowledgements

We thank the intrepid hikers of the Catoctin Mountain: Erin, Ellie, Abby, Maggie, Jo, Paula, Laurie, and Kevin for providing inspiration for this episode. Thomas Eisner’s books “The Love of Insects” and “Secret Weapons” were used as resources for this story.

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Over the last three months, we explored the ecology, behavior, and interactions of Brood X periodical cicadas with humans, other animals, and plants in the eastern United States.  We visited cicadas underground, watched the emergence of cicada nymphs from their subterranean crypts, discovered how male cicadas make noisy and ethereal sounds, learned how to tell the boys from the girls, watched as hungry predators enjoyed the cicada bounty, witnessed mating and oviposition by females, shuddered at their lethal STD, and witnessed havoc wrought upon young trees when females laid their eggs. In the waning weeks of June here in the DMV at locations that had formerly been zones of rollicking cicada choruses a few weeks ago, there is now an eerie silence. The reason for the hush is immediately apparent. Beneath trees and shrubs, the ground is littered with thousands of spent exuviae, the shed skins of cicada nymphs, and the bodies of adult cicadas that survived the onslaught of hungry sparrows, blue jays, hawks, mocking birds, foxes, raccoons, squirrels, dogs, and dozens of other predators. Also scattered about are wings and fragmented body parts of cicadas that were not so lucky. Macabre half cicadas with abdomens transformed into fungal fruiting bodies litter the ground, victims of Massaspora. Hungry ants and maggots repurpose cicada protein and return it to the food web. Along neighborhood roadways and sidewalks greasy black patches mark the spots where cicadas found their final resting place beneath the tires of vehicles or shoes of humans.

What other legacies did cicadas leave behind? For the natural world they provided a bounty for countless predators. This year, birds produced larger clutches more frequently and nestlings were heavier and enjoyed greater survival (Anderson 1977, Strehl and White 1986). As cicadas return to the earth upon death, decomposition of their remains creates a pulse of nutrients to the forest floor boosting microbial biomass, adding nutrients, and enhancing the growth and reproduction of understory plants (Yang 2004). Similar changes in microbial communities occur when cicadas enter streams (Menninger et al. 2008). Young trees took a beating when female cicadas laid eggs in small branches but trees protected by cicada netting were largely spared from this injury (Ahern et al. 2005). Although established mature trees experienced cicada injury, they are able to shrug off this insult in the long run (Clay et al. 2009).

As the door closes on Brood X in 2021, cicadas leave behind billions of holes to aerate the soil, a feast for necrophagous creatures like tiny hungry ants, oily spots along roads where cars were the grim reaper, sidewalks littered with shells and carcasses, and tons of shed skins and decaying bodies that return nutrients to the soil. A solitary late comer to the party wanders amongst earthly remains of its brood mates.  Auf wiedersehen Brood X, until next time in 2038.

For cicadaphiles, this was a season to enjoy a truly remarkable event that happens nowhere else on earth except in the eastern Unites States, only a handful of times in a lifetime. Cicada lovers from as far away as California planned family vacations to enjoy the emergence of Brood X while cicadaphobes tried to cope with the immensity of the event in various ways. Some strove to understand cicadas better and were counseled on how to cope with these red-eyed critters, while others planned a cicada escape. One friend had plane tickets at the ready and when warned that emergence was just around the corner, he departed for a cicada escape to Idaho. For Bug of the Week, it was a welcome break from COVID and other strange events of the past year and a fine time to share a few bug stories. Here in the DMV cicadas had a spectacular run and the teenage offspring of Brood X, 2021 will return in 2038 for their day in the sun.

Acknowledgements

Bug of the Week thanks members of the Cicada Crew, journalists of print and non-print media, neighbors of the Allview community in Columbia, MD, and cicada geniuses that devote their professional careers to studying these strange, whacky, and mysterious insects, who all assisted in the telling of cicada stories. The following references were used to prepare this episode: “Reproductive responses of sparrows to a superabundant food supply” by T. R. Anderson, “Effects of superabundant food on breeding success and behavior of the red-winged blackbird” by C. E. Strehl and J. White, “Periodical cicadas as resource pulses in North American forests” by L. H. Yang, “Periodical cicada detritus impacts stream ecosystem metabolism” by Holly L. Menninger, Margaret A. Palmer, Laura S. Craig, and David C. Richardson,“Effects of oviposition by periodical cicadas on tree growth” by Keith Clay, Angela L. Shelton, and Chuck Winkle, and “Comparison of exclusion and imidacloprid for reduction of oviposition damage to young trees by periodical cicadas (Hemiptera: Cicadidae)” by R. G. Ahern, S. D. Frank and M. J. Raupp.

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With thousands of cicadas chorusing in the treetops this week, male cicadas wooed potential mates and females chose the fathers of their offspring. Within hours of mating, females move to the tips of branches and select soft greenwood terminals about the diameter of a pencil to be the nursery for their offspring. Using a sharp egg-laying appendage called an ovipositor, the female cicada slices narrow slits parallel to the long axis of the branch. She then inserts her hollow ovipositor into the branch and with powerful abdominal contractions, she pumps between 20 and 30 tiny eggs into each slit, creating what is technically known in cicada-speak as an egg nest. Each female has the potential to lay between 200 and 400 eggs during the course of her two to four-week lifespan. In the warmth of summer days and nights, cicada eggs develop and, after six to ten weeks, nymphs hatch and tumble to the earth below.

And now for the dark side of periodical cicadas – plant injury. Injury caused by adults as they sip xylem fluid is inconsequential. The real insult to woody plants comes from the wounds caused by female cicadas when they slice branches to insert eggs. Where densities are great, egg-laying, a.k.a. oviposition, causes tips of many branches to wither and die. Dying and dead terminals droop, resulting in a type of tree injury called flagging. Some injured terminals break and fall to the ground. Branches that do not break may eventually heal, but the wound-site may form a gnarly irregular swelling on the branch.

With the mating game completed, female cicadas fly to small branches where they deposit eggs in egg nests. Using her sharp egg laying appendage called an ovipositor, the cicada slices the branch and then deposits 20 to 30 eggs into each slit to form egg nests.

Which plants are most likely to be affected? The bad news here is that periodical cicadas are broad generalists. Miller and Crowley (1998) studied 140 genera of trees at the Morton Arboretum and found more than half sustained injury caused by ovipositing females.  Among the most severely affected were ones common to landscapes in the DMV, including Acer (maple), Amelanchier (shadbush), Carpinus (hornbeam), Castanea (chestnut), Cercidphyllum (katsura), Cercis (redbud), Chionanthus (fringe tree), Fagus (beech), Quercus (oak), Myrica (bayberry), Ostrya (hophornbeam), Prunus (cherry) and Weigela (weigela). Another study by Brown and Zuefle (2009) of 42 woody plant species added several new genera to the list and found all but 10 species were used by cicadas to lay eggs. This study found that native and non-native woody plants were equally likely to be used for oviposition by cicadas but alien plants, those with no other known congener (plants of the same genus) in the US, were less likely to be hosts for eggs.  

Dense populations of cicadas spell trouble for young trees. Scores of egg nests damage tender branches causing them to wilt, die, and eventually drop from the tree. Withered branches should be carefully pruned from the tree to promote wound closure and encourage restorative growth from axillary buds.

Factors beyond taxonomic identity of a plant affect decisions made by female cicadas regarding where to place their eggs. Small, compact plants often have fewer egg-nests compared to those with longer more open branching habits. Trees at the edges of forests with rapidly growing branches exposed to sunlight often sustain more cicada injury. These trends are easily seen in tree nursery stock and recently transplanted saplings found in yards, commercial landscapes, parks, and transportation corridors, especially those near established trees that historically support cicadas. While ovipositional injury poses a threat to newly planted trees, for older and well-established trees flagging and limb breakage may occur in the short term, however, studies indicate that the long-term threat to tree vitality is minimal (Miller and Croft 1998). Early successional trees exhibited no clear reduction in radial growth or overall growth rates of trees attacked by cicadas (Clay et al. 2009). For small trees and shrubs injured by cicadas, wait until the cicada season ends and remove the injured branches by carefully pruning them back to the nearest node before the cicada injury.

Acknowledgements

Much of the background information for this episode was taken from “Return of periodical cicadas in 2021: Biology, Plant Injury and Management” by Michael Raupp. Other great references include “Does the periodical cicada, Magicicada septendecim, prefer to oviposit on native or exotic plant species?” by W. P. Brown and M. E. Zueffle, “Effects of oviposition by periodical cicadas on tree growth” by K. Clay, A. L. Shelton and C. Winkle, “Periodical Cicada (Magicicada cassini) Oviposition Damage: Visually Impressive yet Dynamically Irrelevant” by W. M. Cook and R. D. Holt, “Effects of periodical cicada ovipositional injury on woody plants” by F. Miller and W. Crowley, and “The ecology, behavior and evolution of periodical cicadas” by K. S. Williams and C. Simon. We thank Randy and all the good folks in the Allview neighborhood for allowing us to visit, photograph, and film cicadas in their landscapes.

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This week cicadas have taken to wing, dashing across yards, roadways, and landscapes as they try to hook up with other members of their species. While standing beneath a raucous chorus of Magicicada cassini, a gentle sprinkle wafted down on my head, kind of a summer shower on a hot day provided by the periodical cicadas. Thinking back to John Fogerty’s 1970 lyrical query “I wanna know, have you ever seen the rain, comin’ down on a sunny day”, I mused about what exactly was behind a cicada shower? Recall that cicada nymphs feed on a nutrient poor fluid carried in a vascular tissue called xylem. Developing nymphs process large amounts of this liquid to gain sufficient nutrients to grow. Now consider the needs of the adult cicada. While living a normal life span of two to four weeks, they must mature, find mates, defy death from the jaws of predators, and, for the females, fly to trees to find suitable locations to deposit several hundred eggs. These activities are conducted in sometimes scorching heat that can exceed 90 degrees Fahrenheit. Clearly, cicada adults need some sort of fuel to undertake all these activities in just a few short weeks.

With almost all cicadas up and out of the ground, noisy cicadas are busy flying throughout the landscape to find their brood mates. Hundreds line the trunks and branches of trees to feed and find mates. First at full speed and again at half speed, watch as one female rids herself of liquid waste – a.k.a. cicada pee. Our periodical cicadas produce a gentle shower of pee, but large cicadas of the Costa Rican rainforest can deliver a firehose-like torrent of pee.

Some common lore has it that adult cicadas do not feed; however, adults do indeed feed. Soda-straw-like mouthparts are inserted into the plant’s xylem vessels and a massive pump in the head of the cicada creates negative pressure to suck xylem fluid from vessels located in tree branches and along the trunk, into the digestive tract of the cicada. Xylem fluid replaces moisture lost from these small creatures as they respire and move about. To survive above ground they process vast quantities of fluid. Their specialized digestive tract enables them to suck copious amounts of sap from trees and then rapidly excrete the excess fluid. “Pee” is a term usually applied to urine, a liquid produced by the kidneys of vertebrates to rid the body of metabolic waste products. Cicadas and other members of the Hemiptera clan produce liquid waste. Specialized organs called the malpighian tubules remove waste products from the hemolymph of the cicada and pass it to the colon for excretion. Sucking insects such as aphids and soft scales feed on another vascular fluid called phloem and produce a waste product called honeydew. This sugar-rich liquid is quite different from that produced by cicadas and other xylem feeders. For periodical cicadas, their liquid waste is not exactly “pee”. However, amidst the Brood X cicada chorus, don’t be surprised if you see and feel rain comin’ down on a sunny day.  

Acknowledgements

Bug of the Week thanks Dr. Shrewsbury for inspiring this episode and Randy, ruler of all cicadas, for allowing us to photograph and record cicadas in her beautiful landscape. 

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