Eerie green lights along the Potomac: Glow-worms, larval Lampyridae

 

A pair of glow-worms team up to enjoy a tasty earthworm meal.

 

Earlier this year we met fantastic fireflies. They appeared to enjoy a very good year in many parts of the DMV, including my yard in Columbia, MD. In addition to serving as a way to find a mate, the bioluminescence of fireflies also serves as a warning signal to predators. Attacking this tempting, flashy meal could turn out to be a nasty surprise. You see, many species of fireflies are chemically protected and rendered unpalatable by noxious chemicals known as lucibufagins. Last week while enjoying a moonlit stroll along the towpath of the Chesapeake and Ohio Canal which boarders the mighty Potomac River, eerie green lights winked on and off amongst the vegetation. Upon closer inspection, the source of this spectral display turned out to be generated by the immature stages of fireflies, larvae called glow-worms. Unlike the vivid light produced by adult fireflies, the C&O glow-worms produced an intermittent spark of soft, greenish light. Judging by their size, these largish larvae were likely the offspring of fireflies that deposited eggs in the soil during the summer of 2023. Many glow-worms in our region require two summers to develop.

Along a towpath bordering the banks of the mighty Potomac River, eerie green lights on the ground mark the location of glow-worms. The red dot is produced by the video camera. Light is produced by white luminescent organs beneath the abdomen of the larva. Daylight gives us a better look at the fast-moving glow-worm. Watch as a pair of glow-worms feast on an earthworm. Neurotoxins injected into the worm through sharp hollow jaws immobilize the prey. Digestive enzymes secreted by the larva liquify the worm’s tissues, and then the glow-worms slurp their liquid feast. Glow-worms help rid our gardens of pests like slugs, snails, and other soil-dwelling insect pests.

Glow-worms produce their eerie lights with paired luminescent organs on the underside of their abdomen.

We all have heard the tales of fireflies using distinct patterns and colors of luminescent flashes to recognize and find mates. But why would juvenile beetle larvae engage in flashy displays? These youngsters were obviously too young for the adult firefly mating game. Scientists discovered that immature stages of fireflies, glow-worms, like their adult counterparts, are also distasteful to many kinds of predators including ants, birds, rodents and amphibians. Their eerie flashing lights serve as a warning to hungry would-be predators not to attempt an attack unless they desire nasty tasting meal. Paired luminescent organs on the underside of the glow-worm’s abdomen produce the green light, which serves as a warning.

In addition to being a little creepy and pretty cool, glow-worms are highly beneficial in your garden and in crops where they eat many soft-bodied invertebrates including slugs, snails, and other soil-dwelling insect pests. I invited a pair of glow-worms into my home to spend a little time with me. Over the course of several days, they consumed many types of prey, including maggots and earthworms. Some of the earthworms were quite large and I wondered how they wrangled large prey. It turns out that glow-worms use sharp hollow jaws to inject prey with paralyzing neurotoxins. Once immobilized, digestive enzymes are secreted via their mouthparts into the victim to help liquify its body tissues. The resulting nutrient rich broth is then slurped up into the larva’s digestive tract. Yum!

If you enjoyed fireflies in your landscape this summer, consider taking a walk outdoors on a starlit night and maybe you will be treated to the ethereal light of the glow-worms in your lawn or flower bed.

Acknowledgements

Bug of the Week thanks Dr. Shrewsbury for providing text used in this episode and wrangling glow-worms featured herein. The fascinating writings “Bioluminescence in Firefly Larvae: A Test of the Aposematic Display Hypothesis (Coleoptera:Lampyridae)” by Todd J. Underwood, Douglas W. Tallamy, and John D. Pesek, and “ Glow-worm larvae bioluminescence (Coleoptera: Lampyridae) operates as an aposematic signal upon toads (Bufo bufo)” by Raphael De Cock and Erik Matthysen, “Flash Signal Evolution, Mate Choice, and Predation in Fireflies” by Sara M. Lewis and Christopher K. Cratsley, “How to Overcome a Snail? Identification of Putative Neurotoxins of Snail-Feeding Firefly Larvae (Coleoptera: Lampyridae, Lampyris noctiluca)” by Jonas Krämer, Patrick Hölker, and Reinhard Predel, and “For the love of insects” by Thomas Eisner served as resources for this Bug of the Week.

Field crickets invade a home with a wake-up call: Fall field cricket, Gryllus pennsylvanicus

 

While some home invaders are unwelcomed guests, the annual visit by field crickets always provides a bit of alright for me.

 

Melodious male crickets bear a multi-ridged structure called the file on one forewing. The opposite forewing bears a hardened structure called the scraper. As wings open and close, the file moves across the scraper creating vibrations, or chirps, that resonate from the cricket’s wings.

Despite my profound fondness for almost all things six-legged, a 4:30 am wake-up call courtesy of a field cricket in the bathroom did make me a bit peevish. It also heralded the vanguard of the usual annual invasion of arthropods that assault my home each autumn. With sleep seriously disturbed, I seized the opportunity to see how well chirps of this diminutive troubadour tracked ambient temperature. Here’s the backstory of how it works. As you know, insects are cold blooded. Their body temperature is more or less the same as the environment that surrounds them unless the insect is basking in the sun or using muscles to elevate its temperature like the dobsonfly we met in a previous episode. Many years ago, a noted entomologist, Richard Alexander, demonstrated a simple relationship between ambient temperature and the how often a field cricket chirped. Simply count the number of chirps in 15 seconds, add 37, and you will approximate the ambient temperature in degrees Fahrenheit. Although I tracked down the diminutive troubadour behind the toilet, he developed a severe case of stage-fright when he saw the camera and refused to perform. Undeterred from my quest, I slipped on a pair of crocs and went outside where a complete ensemble of field crickets chirped away in the flower bed. Darkness prevented visual contact with the crickets but their songs were loud and easily recorded. I selected two singers and recorded each 20 times at intervals of 15 seconds. A rather warm-blooded cricket averaged 34 chirps per 15 seconds which estimated the temperature to be 71 degrees (34 + 37 = 71). Nearby a cooler cat reported in with 28 chirps per 15 seconds, estimating the temperature to be 65 (28 + 37 = 65). A digital thermometer placed on the ground in the flower bed showed an ambient temperature of 69 degrees. One cricket too warm, one cricket too cool, but when you take the average, just as like in Goldilocks and the three bears, the average cricket estimate of 68 was just about right.  

While my sleep-interrupted cricket failed to perform, on another occasion a less shy field cricket was happy to tell me the temperature inside my home. Watch the accompanying video to see how well he estimated the temperature on my kitchen counter. 

This little field cricket demonstrates his skill at helping humans estimate ambient temperatures. Counting the number of chirps in 15 seconds and adding 37 provides an estimate of ambient temperature. Let’s see how well this works: 32 chirps plus 37 equals 69 degrees Fahrenheit. My digital thermometer read 73 degrees above the kitchen counter. Maybe this little guy was just a cool customer.  

Although some might think so, helping humans figure out ambient temperature is unlikely the reason why crickets chirp. A few years ago, I tracked two male crickets, one of which was missing a hind leg, and a nearby female cricket. Never one to stand in the way of romance, I captured the trio and placed them in a small terrarium. Within moments the smaller male, the five-legged fellow named Pete, challenged his cohabitant, Bud, to a duel that resulted in boisterous chirping, snapping of jaws, and grappling with forelegs. The more aggressive Bud soon vanquished his challenger and Pete retreated to a quiet corner of the terrarium. Crickets battle for food and mates and chirping is a part of this. For centuries Chinese gamblers have wagered high stakes on the outcome of cricket fights. An interesting trick used by the cricket handlers to resuscitate losers of bouts is to shake the defeated warriors and toss them in the air several times. This dramatically reduces the recovery time and allows the small combatants to return to the arena in minutes rather than the regular convalescent period of hours or days. A study published in Nature confirmed the success of this therapy in helping defeated crickets regain their fighting spirit. 

In addition to wooing mates, some cricket chirps warn interlopers to get lost!

Rather than interrupt Nature’s course, I allowed Pete to sulk in the corner. Shortly after his victory, Bud initiated a series of soft chirps and his efforts were soon rewarded by a visit from Wendy, the demure female cricket. What useful information is carried in the male cricket’s song other than the typical male plea for female attention?  A fascinating study by two Finnish scientists of the Mediterranean field cricket, Gryllus bimaculatus, found a link between the male cricket’s song and his immune response. Troubadours with a highly attractive song also had superior immune systems. If the ability to ward off diseases due to superior immune function is passed along to progeny, then females that choose a mate with an enhanced immune system may ensure better survival of their offspring. By demonstrating his superior immune system with a song, the male cricket may win the lady. 

One last thought about the cricket and his song relates to Old Man Winter, whose return brings much insect activity to a grinding halt. Once winter’s chill arrives and temperatures plummet, crickets will not be chirping at all. So, now is a great time to enjoy songs of crickets, day and night, maybe even those reverberating from troubadours in the bathroom.               

Acknowledgements 

The following articles were used in preparation for this Bug of the Week: “Courtship song and immune function in the field cricket Gryllus bimaculatus” by Markus Rantala and Raine Kortet, “Aggressiveness recovers much faster in male crickets forced to fly after a defeat” by Hans A. Hofmann and Paul A. Stevenson, and “Seasonal and daily chirping cycles in the northern spring and fall field crickets Gryllus veletis and Gryllus pennsylvanicus” by Richard Alexander and Gerald Meral.

From the Bug of the Week Mailbag: Who’s been munching on my deck? Dogwood sawfly, Macremphytus tarsatus

 

An almost fully developed dogwood sawfly larva checks out a deck to find the perfect spot to construct its winter refuge in wood. Image credit: Bob Causer

 

Several small pock marks reveal locations where dogwood sawflies attempted to construct overwintering galleries in a deck. Image: Bob Causer

Herbivorous insects are full of surprises. Who would have guessed that a leaf munching larva spends another part of its life cycle boring in wood to build a place to hang out in winter? Not me, but this is how the dogwood sawfly rolls. A few weeks ago, I received great images of a dogwood sawfly larva and a report that it was gnawing holes in a deck and generating piles of sawdust. Other encounters with sawflies here at Bug of the Week include ones with sawfly larvae munching on mallows, crushing columbines, and ravaging roses.

Sawflies are primitive members of the bee and wasp order of insects known as the Hymenoptera. Unlike their kin, who feast on the flesh of other arthropods or dine on the nectar and pollen of plants, several families of sawflies feed on leaves. One of the favored hosts of dogwood sawfly is grey dogwood, Cornus racemosa, but silky dogwood, Cornus amomum, and flowering dogwood, Cornus florida, are also on the menu. Dogwood sawfly larvae spend their summer devouring dogwood leaves, initially in chummy groups that skeletonize leaves, but as they grow larger, they may eat the entire leaf with the exception of the midvein. Winter is spent as a larva ensconced in a chamber, or “cell”, built in rotting wood or sometimes structural wood including siding, or as in the case of this week’s star, decks.

Early in their development dogwood sawflies like the one on the right are cloaked in white wax. Later they lose their wax. Watch as these snaky sawflies practice their curls beneath a leaf. An almost fully developed larva waves to the camera while searching for another meal. In autumn before leaf-fall, they build galleries in wood to spend the winter. Notches in this deck bear witness to their attempts.

An easy way to tell the difference between caterpillars (the larvae of moths and butterflies) and sawfly larvae, is to count the pairs of appendages called prolegs on their abdominal segments. Caterpillars like the larva on top have five or fewer pairs of prolegs. Sawfly larvae like the one below usually have six or more pairs of prolegs.

In spring, the larvae pupate and adults, resembling small wasp-like insects, emerge to fly and find mates from May through July. Females insert their eggs in the undersurface of dogwood leaves in batches numbering 100 or more. Eggs hatch and larvae consume leaf tissue and develop through several growth stages, or instars, over the summer. With the approach of autumn and imminent leaf drop, large mature sawfly larvae wander from dogwood trees to construct overwintering redoubts in wood. Although many sawfly larvae bear a striking resemblance to caterpillars, larvae of moths and butterflies, most can be distinguished from Lepidoptera larvae by the number of pairs of appendages called prolegs found on abdominal body segments. In addition to three pairs of jointed walking legs on the thorax, most caterpillars have five or fewer pairs of fleshy prolegs on their abdominal segments. By contrast, in addition to the requisite three pairs of thoracic legs, most sawflies bear six or more pairs of prolegs.

Beautiful dogwood sawfly caterpillars assume their characteristic curly pose between bouts of defoliating dogwoods.

 As larvae, dogwood sawflies have, quite literally, a colorful juvenile history. After hatching from eggs, larvae are rather translucent yellowish creatures resembling gummy worms. As they develop and molt, specialized glands produce a snowy-white cloak of wax. Fully developed larvae shed the white waxy cloak and assume a dashing color scheme of yellow, white, and black. Why the chameleon routine? Well, some scientists have speculated that the brilliant white coloration and elongated body of young larvae may mimic a bird dropping and reduce the chance of predation. What self-respecting bird eats bird droppings, right? Another hypothesis suggests predators and small parasitic wasps may be unable or unwilling to effectively attack sawfly larvae through their cloak of wax. As dogwoods get ready to shed their leaves in the next few weeks, keep an eye out for these beautiful and interesting creatures.

Acknowledgements

Bug of the week thanks Bob Causer and Virginia Brace for providing images and inspiration for this episode. Thanks also to our friend Jimmy who shared his dogwood and its sawflies. The interesting articles “Be Alert for Dogwood Sawfly” by Joe Boggs, and “Insects that feed on trees and shrubs” by Warren Johnson and Howard Lyon were used as sources of information for this story.

Fright and fun courtesy of flying spotted lanternflies, Lycorma delicatula

 

Encounters with humans often result in lanternflies feeling a little flat. Image: Paula Shrewsbury, UMD

 

Last week Bug of the Week received a text regarding swarms of spotted lanternflies visiting children and adults at a public park in Carroll County, Maryland. Sure enough, a trip to the park revealed squealing kids, nervous parents, and scores of spotted lanternfly adults flitting about and landing on slides, swings, play sets, and people. While some children screeched and ran, others delighted in the heavily promoted and much-heralded sport of chasing down lanternflies and squashing them. What fun! Ah, but not all children embraced an ant-bully mien. While recording a lanternfly climbing up my leg, a youngster nearby asked if he could have one on his leg, too. Nice to meet a budding entomologist!

As one youngster said, “there’s a thousand of them….” Lanternflies take flight in late summer and autumn. When lanternflies invaded a playground in Maryland some children shrieked and ran while others laughed and tried to catch some. What strange attraction brought lanternflies to playsets, slides, and people remains a mystery. A memorable time was had by all, fearful and fun-loving alike, except perhaps, the lanternflies flattened by sneakers, flipflops, and baseball caps.

Why spotted lanternflies invaded this playground in Maryland remains a mystery. Image: Paula Shrewsbury, UMD

What causes spotted lanternflies to abandon a site and engage in flight, swarming to new locations? Fascinating studies by scientists in Pennsylvania reveal some of the secrets to the autumnal movements of adult spotted lanternflies. Thomas Baker and his colleagues at Penn State discovered that the long-distance airborne lanternflies were primarily slim unmated females. These fliers were capable of flights ranging from roughly 30 to 150 feet. Their spontaneous flights were believed to be quests to find suitable hosts, plants that could supply sufficient nutrients for them to fatten up and deposit a complete complement of eggs before cold weather put an end to their mischief. The Penn State team also assessed the flight worthiness of plump yellow-bellied lanternflies. These females were full of developing eggs. A vast majority of these heavy females had successfully mated but their ability to fly was weak and limited to only about 12 feet when launched into the air.  According to lanternfly expert, Dr. Kelly Hoover, spotted lanternflies may undertake long-distance flights when their sustained feeding has depleted resources in trees and they fly to find better quality food resources in trees elsewhere.

On a sunny late summer afternoon in a restaurant park in scenic Rohrerstown, PA, spotted lanternflies were on the wing. They crashed into windows, wandered on sidewalks, and met gruesome ends beneath human feet and tires of vehicles. Wanderers displayed their impressive jumping skills when harassed by a giant finger and one contemplated a trip to New Jersey on the rear bumper of my car.

Since its discovery in Berks County, Pennsylvania in 2014, spotted lanternfly has established populations in locations more than 600 miles away. New York State Integrated Pest Management Program of Cornell University.

While autumnal spontaneous flights have been witnessed on a regular basis, these relatively short distance flights of hundreds of feet likely account for only a minor component of the spotted lanternflies’ spread through the United States. From their initial discovery point in Berks County, PA in 2014, isolated spotted lanternflies infestations have popped up in midwestern and southern states more than 600 miles away. The most likely explanation for these long-distance peregrinations lies in human-assisted transport of lanternfly eggs. Unlike many herbivorous insects that lay eggs on food plants for their young, spotted lanternfly mothers deposit egg masses on non-host objects including stones, cinder blocks, lawn furniture and vehicles, in addition to trees. These nondescript masses of eggs are easily overlooked on natural and human-made items and easily transported inadvertently by road or rail. Recently, a metal sculpture festooned with spotted lanternfly eggs being shipped from New York to Sonoma, California was intercepted at the border before entering our leading wine producing state. Great work by the California Department of Food and Agriculture at the Truckee Border Station.

Why this particular playground attracted hordes of flying lanternflies remains a mystery. A similar play area less than 300 yards way was devoid of these critters and also devoid of children. Maybe lanternflies just saw the kids having a good time and wanted to join in the fun. Who knows?   

Acknowledgements

Special thanks to Brian and Jackie for providing the inspiration for this episode and to the children playing at the park who shared their excitement and trepidation. Thanks to Dr. Paula Shrewsbury for providing images of lanternflies. The fascinating articles “Flight Dispersal Capabilities of Female Spotted Lanternflies (Lycorma delicatula) Related to Size and Mating Status” by Michael S. Wolfin, Muhammad Binyameen, Yanchen Wang, Julie M. Urban, Dana C. Roberts, and Thomas C. Baker, and “Spotted lanternfly collective flights in late summer not dangerous to public” by Amy Duke were used to prepare this story. Thanks to Brian Eshenaur and the entire team at the New York State Integrated Pest Management Program of Cornell University for providing the updated maps of spotted lanternfly in the US and to the Entomological Society of America for providing the map of the potential distribution of spotted lanternfly in the US.

West Nile Virus and other Fly Borne Diseases in the News - Beware of disease vectors: the Northern House mosquito, Culex pipiens, Asian Tiger mosquito, Aedes albopictus, and other biting flies

 

Hungry Northern House mosquitoes, vectors of West Nile virus, are thriving and on the hunt for blood.

 

At only a few millimeters in length, tiny no-see-um midges can carry serious human viruses including the strange sloth fever virus.

Last week news agencies carried warnings about an uptick in mosquito borne diseases following reports that famed immunologist Dr. Anthony Fauci recently contracted and survived a bout of West Nile virus. As of August 27, 2024, 289 cases of West Nile virus in 31 states had been reported with Texas, Mississippi, and Nebraska leading the way. Even more disturbing was the recent demise of a citizen in New England from another mosquito borne illness, Eastern Equine Encephalitis. Recent travelers to Cuba have contracted another virus called sloth fever, a.k.a. Oropouche virus, carried by small biting flies called no-see-ums which we met in a previous episode. As record heat continues in our land, generation times shrink for mosquitoes. More mosquitoes are produced in shorter periods of time. Drenching storm systems create abundant breeding sites for aquatic mosquito larvae. Together, heat and rainfall provide the perfect storm for elevating populations of mosquitoes in many parts of our nation. Let’s learn a little more about mosquitoes, the risks they pose, and how to avoid their bites and the illnesses they carry.  

Historically, September is the second most common month to contract West Nile virus. Image courtesy of Centers for Disease Control

Mosquitoes are more than just a nuisance and several species carry important diseases such as West Nile Virus. According to the CDC, following its discovery in the United States in 1999, more than 59,000 cases of West Nile Virus have been reported and more than 2,900 deaths associated with West Nile Virus have occurred. While most of us shrug off West Nile virus with little or no symptoms, it can be severe and even lethal to seniors and certain others. Researchers have suggested that some seniors and people with compromised immune systems may lack sufficient immune responses to thwart the West Nile Virus.  

Watch as a female Culex pipiens form molestus extracts all the blood she needs to produce the next batch of eggs and then scurries away to the shadow of a knuckle to hide. Filmed at twice life speed.

Asian tiger mosquitos are active during daylight hours. They vector important human diseases including dengue, chikungunya and Zika.

Many species of mosquitoes prefer to feed at dusk and you can avoid being bitten by staying indoors in the evening. However, unlike many of our native mosquitoes, the exotic Asian Tiger is a daytime biter, adding hours of itching, scratching, and swatting to days in the garden. Protect yourself from aggressive biters by wearing light-weight, long-sleeved shirts and pants when working outdoors. Certain brands of clothing are pretreated with mosquito repellents such as permethrin. I have worn these in tropical rainforests where mosquitoes were ferocious and they really did help. Many topical insect repellents can be applied to exposed skin before you go outdoors. Some will provide many hours of protection, while others provide virtually none. Some repellents should not be applied to children and you should always help kids apply repellents. Do not apply repellents containing DEET under clothing. To learn more about mosquito repellents, click this link to see repellents recommended by the Centers for Disease Control. For safety, be sure to read and follow the directions on the label of the repellent before you apply it to people or clothing.  

If you dine outdoors, place a fan on your patio. The light breeze created by the fan will greatly reduce the number of mosquitoes flying and biting. Many traps are also available to capture and kill mosquitoes. Some rely on a light source to attract blood seekers. However, many types of moths, flies, and beetles are attracted to light. Mosquitoes, unfortunately, do not use light to find their meals and are NOT readily attracted to light traps. One study demonstrated that less than 1% of the insects attracted to light traps were biting flies such as mosquitoes. This study estimated that light traps kill billions of harmless and beneficial insects each year. Actually, blood seeking mosquitoes are attracted to odors emanating from the host. As we move about the earth, we release many odors, including carbon dioxide and lactic acid that are detected and followed by hungry mosquitoes to find us. Some mosquito traps release carbon dioxide and will attract and catch many mosquitoes. Female mosquitoes ready to lay eggs are attracted odors emanating from water sources. A clever trap called a Gravid Aedes Trap (GAT) has been used in community-wide programs in the DMV to reduce local populations of Asian Tiger mosquitoes. Females fly into these traps to lay eggs but never escape. Sounds like Hotel California for these tiny vampires.  

Wheelbarrows and pails full of water? Dump them now! They are nurseries for mosquito larvae.

To reduce the chances of mosquitoes breeding around your home, eliminate standing water by cleaning your gutters, dumping your bird bath twice a week, inverting your wheelbarrow and getting rid of water filled containers. If you have an aquatic water garden or standing water on your property that breed mosquitoes, you can use a product containing the naturally occurring soil microbe known as Bacillus thuringiensis israelensis a.k.a. Bti. Bti comes formulated in doughnut-shaped tablets that can be placed in water to kill mosquito larvae. 

A garbage pail lid full of water becomes the perfect nursery for a crop of Culex mosquitoes. Two egg rafts contain scores of eggs ready to hatch. Nearby, fleets of mosquito larvae called wriggles filter tiny particles of food from the water. In just a few short weeks, this lid will be bustling with fully developed wrigglers suspended beneath the water by breathing siphons. Amidst the milieu, zany mosquito pupae called tumblers bumble about. With continued hot weather and ample rainfall, adults will emerge, and yes, there will be blood.   

With continued hot weather and ample rainfall, mosquitoes will be present for several more months. Be on the lookout and take precautions now to avoid being bitten. 

Acknowledgements 

Several interesting articles were consulted for this episode including “How the body rubs out West Nile virus” by  Nathan Seppa, “Toll-like Receptor 7 Mitigates Lethal West Nile and Encephalitis via Interleukin 23-Dependent Immune Cell Infiltration and Homing by Terrence Town”, Fengwei Bai, Tian Wang, Amber T. Kaplan, Feng Qian, Ruth R. Montgomery, John F. Anderson, Richard A. Flavell, and Erol Fikrig, “Density and diversity of non-target insects killed by suburban electric insect traps” by Timothy B. Frick and Douglas W. Tallamy, and “Neighbors help neighbors control urban mosquitoes” by Brian J. Johnson, David Brosch, Arlene Christiansen, Ed Wells, Martha Wells, Andre F. Bhandoola, Amy Milne, Sharon Garrison & Dina M. Fonseca. Information on the geographical and seasonal occurrences of West Nile Virus came from the data rich CDC websites.

To learn more about the mosquitoes and how to defeat them, please view the following video, B.I.T.E. mosquitoes before they bite you!