Fireflies are busy flashing for mates! Lampyridae spp.

 

An adult of the common eastern firefly, Photinus pyralis. In this picture, the head is sticking out from underneath the shield-like projection of the thorax.

 

This week’s episode comes to you from Dr. Paula Shrewsbury, Entomologist at the University of Maryland, College Park, who created this great article for her “Beneficial of the Week” in the IPM Alerts - Landscape & Nursery.

 “Fireflies have been lighting up my neighborhood (Howard Co. MD) since the first week of June. It looks like a good year for fireflies based on the amazing display of flashing lights I see every night. Usually around 8:00 p.m., just before my 3-year-old grandson’s bedtime, the flashing begins. It has become a ritual that before bed, we go outside and catch fireflies. Most of us have fond memories of catching fireflies as a kid and putting them in glass jars, which were kept by the bed to watch during the night.

Watch fireflies light up a small patch of landscape in front of my bed of perennials. Firefly larvae hunt soil-dwelling pests in that flower bed. Video compressed three times actual speed.

 Fireflies, also known as lightning bugs, are really neither bugs nor flies. They are characterized as soft-winged beetles in the order Coleoptera and the family Lampyridae. There are over 2,200 known species of fireflies, of which about 165 species have been reported in the U.S. and Canada. Fireflies are found in temperate and tropical regions and in the humid regions of the Americas, Asia, and Europe. In the U.S., the abundance of fireflies is greater east of the Great Plains than in western states. Interestingly, fireflies that produce light are uncommon in western North America. Some firefly species are diurnal, and therefor have no need to create light. These species are known as daytime dark fireflies and they use chemical pheromones for mate attraction. Although the adults do not light, the larvae do glow at night, similar to eastern species.

Underside view of an adult firefly showing the abdomen where the light organ is located (white segments).

 Most flashing species occur east of the Mississippi River, are about ¾” in length and are active at dusk and night. Adults and larvae of many firefly species exhibit bioluminescent – they glow in the dark! Many organisms such as bacteria, fungi, jellyfish, algae, fish, clams, snails, crustaceans, and of course insects, exhibit bioluminescence. Firefly species have special light organs that make the underside of their abdomens light up. How do fireflies make light? The light emitted by a firefly is actually a chemical reaction in the beetle’s abdomen. The light organ has special cells that contain a chemical called luciferin. An enzyme called luciferase combines oxygen with luciferin in these cells to create light. Scientists actually do not know how fireflies regulate their lights to turn them on and off. You might have also noticed how “cold” the light looks. This is because no infrared (or heat) or ultraviolet frequencies of light are emitted. Among the light-producing fireflies, lights are yellow, green, or pale red.

 The purpose of this bioluminescence varies. It is believed that the flashes are part of a signaling system for attracting mates. Both males and females emit light intermittently or in specific flash patterns. The rhythmic flash patterns produced are specific for each species of firefly and vary by sex within a species. The flashes that we see are from the males that are attempting to attract a mate. For example, males of the common eastern firefly (Photinus pyralis) flash every six seconds. Females watch the light “show” and if a display from a specific male is particularly attractive, she will flash a response but only if it is from the male of the same species. The male descends to that location to mate with her. In addition to transferring sperm to the female during copulation, the male offers a nuptial gift of rich protein, which the female uses to provision the eggs that will soon start to develop in her ovaries. Interestingly, in one species of firefly, Photuris pensylvanica, the female mimics the flash pattern of another species, Photinis pyralis, to attract the male of the other species to her. When the male of the other species arrives, thinking he has found his mate - she eats it to obtain defensive compounds used to protect her eggs. A bad surprise for that male!

During daylight hours fireflies can be found patrolling leaves. By night, a flashing male firefly searches for a female. After locating his mate on an overhanging leaf, the courtship deal is sealed and the flashers turn off the lights for an intimate interlude. Watching insect behavior is really fascinating.

Glow-worms, larvae of fireflies, are predators that live in the soil and search for prey.

 For the common eastern firefly, eggs are laid in moist soil and hatch about a month later. All immature fireflies (or larvae) are called glow-worms (see image). The larvae emit light too, though it is a low intensity glow rather than flashing like adults. The larvae of our eastern firefly develop over two summers, so they overwinter twice, before pupating and emerging as adults this time of the year. Most fireflies are reported to pupate in rotting logs or the furrows in the bark of tree trunks. Although the larvae of fireflies are referred to as glow-worms, technically this is not quite correct. Glow-worms are a type of firefly where the adult female is flightless and maintains the appearance of a larva and she emits a long-lasting glow, similar to larvae. The males have the appearance of an adult firefly. To make it more confusing, other insect larvae that glow are sometimes called glow-worms too.

 Why are fireflies considered beneficials? Well, the soil active firefly larvae, or glow worms, are voracious predators of soft-bodied invertebrates and known to feed on slugs, snails, worms, and other soil-dwelling insects. Glow worms use their mandibles to inject prey with a paralyzing neurotoxin, making it defenseless, and then secrete digestive enzymes that liquify the prey making it easier to consume. Firefly larvae or glow-worms are believed to glow as a warning signal telling predators not to eat them, as they are mildly toxic and taste nasty. It is not well known what all adult fireflies feed on but some feed on pollen and nectar and some are reported not to feed at all. 

 Since most fireflies that produce light are in the Eastern U.S., it makes the nightly light shows we encounter here something special to behold for a few weeks during spring and early summer. Be sure to help young people you know, and others, enjoy the experience of observing and collecting fireflies. Be certain to release the little lights when you are done!”

 Acknowledgements

 Bug of the Week thanks Jackie for providing the inspiration for this episode. The interesting articles “Experimental tests of light-pollution impacts on nocturnal insect courtship and dispersal” by Drs. Aerial Firebaugh and Kyle Haynes, “Flash Signal Evolution, Mate Choice, and Predation in Fireflies” by Sara M. Lewis and Christopher K. Cratsley, and fascinating studies of Dr. Sara Lewis and Dr. Thomas Eisner and their colleagues, served as resources for this Bug of the Week.

Return of the monarda marauder: Raspberry pyrausta, Pyrausta signatalis

 

Eggs laid in buds of leaves and flowers by the pretty raspberry pyrausta moth hatch into hungry caterpillars ready to pillage monarda foliage and blossoms. Image: Paula Shrewsbury, PhD

 

After a few seasons of respite for my monardas, the raspberry pyrausta has returned with a vengeance to my perennial flower beds. For readers that love spotted beebalm, scarlet beebalm, and wild bergamot, this week we visit a pesky small caterpillar and learn some ways to help safeguard the blossoms of these wonderful perennial plants.

A small creamy colored caterpillar is the marauder feasting on my flowers.

Why should we protect the blossoms of monardas? By providing rich nectar rewards, these delightful natives are magnets for an astounding array of beneficial animals ranging from hummingbirds and gold finches to butterflies, bumble bees, hover flies, and myriad predatory and parasitic wasps. I have watched the summer parade of interesting and beautiful insects visiting monardas for hours over a cup of coffee on sunny summer mornings. But every year, there is foul-play afoot in my flower beds. Sometime in the latter days of May and early days of June just as the bergamot was prepping to bloom, developing flower buds, attendant sepals, and supporting leaves became shredded and riddled with holes. Close examination of the buds revealed tiny black pellets lodged in the nooks and crannies of the flower heads. Now, to bug geeks, tiny black pellets usually are a sign of insect activity. Said pellets are actually the excrement, a.k.a. frass, of caterpillars feeding within the flower buds. Some further poking around the nascent blossoms revealed small creamy colored caterpillars hiding in the axils of sepals and at the bases of florets.

While identification of small caterpillars presents a challenge even to seasoned entomologists, identification of adult moths and butterflies is way easier. A more extensive search of the bergamot patch revealed a rather pretty raspberry pyrausta moth, a member of the crambid moth clan. Crambid moths, also known as snout moths, are named for the elongated mouthparts protruding from the front of their head. Many bore into the stems of grasses and other monocots and some, such as the European corn borer and sod webworm, are serious agricultural and lawn pests. Just one or a few of these caterpillars feeding within a developing flower bud are sufficient to all but ruin its floral display.

While some blossoms on my bergamot look fine many are ravaged. This culprit is a small caterpillar feeding in the flower head. Chewed florets, holes in leaves, silk and pellets of frass are telltale signs of the caterpillar. Regular inspections and crushing caterpillars when you find them will help keep your blossoms looking fine.            

Early generations of the raspberry pyrausta defoliate leaves and distort developing terminal buds.

Here is the dilemma. For many herbivores in my landscape, the death sentence is commuted under a live-and-let-live policy with the belief that even pests will become food for other insects or birds higher in the food web. However, in the case of the raspberry pyrausta, lack of intervention translates into few or no blossoms on monardas and few or no resources for pollinators, predators, and parasitoids dependent on nectar and pollen for their activity and survival. So, in this case the caterpillars gotta go to make way for the beneficial insects. Ridding the blossoms of caterpillars is fairly easy to do. As flower heads begin to form in late spring and early summer watch out for holes in leaves, feeding damage to developing florets, and small black frass pellets accumulating in the axils of leaves and sepals. Carefully search the flower head and when you locate the caterpillar, simply crush it. If you don’t like touching insects, don a pair of rubber gloves and do the deed. Mechanical destruction of the pest is foolproof and works well in small patches. For larger patches, you could consider using an insecticide listed by the Organic Materials Review Institute (OMRI) for controlling caterpillars. These insecticides have been reviewed by scientists and approved for use in the production of organic food crops. Two of my favorites contain the active ingredient Bacillus thuringiensis kurstaki (Btk) or spinosad. Btk is derived from a common soil microbe and it works well on many species of caterpillars. If you grow milkweeds as a source of food for monarch caterpillars in your flower beds, take care not to spray Btk on your milkweed lest you poison any resident monarch larvae.

Some brands of spinosad will also carry the OMRI stamp of approval and they work well on caterpillars. Spinosad is also a product of a soil microbe. This molecule attacks the nervous system of insects. But be careful with spinosad, as it is highly toxic to bees. If other plants in your garden are in bloom or are about to bloom, avoid drift that might contact and harm charismatic pollinators. Use the same caution with monarda. The pyrausta will be present in the early formation of flower buds but as florets form and mature, avoid using spinosad as bloom time approaches and certainly when flowers are in bloom. Many snout moths have multiple generations and in my experience the raspberry pyrausta is no exception. I have crushed several crops of caterpillars in the flower buds and just the other day, a few more adult moths dared to flit around my flower bed. For a bug geek, watching the sunrise on a warm summer morning while sipping some coffee and squashing some caterpillars is not a bad way to start the day.

Is the Jorō spider coming to your neighborhood? Trichonephila clavata

 

Despite what you may have heard, the Jorō spider is docile and poses no known threat to humans or pets. Image credit: David Coyle

 

Last week a team of scientists from Southern Adventist University, University of Florida Lake Alfred, University of Texas El Paso, Clemson University, and an unaffiliated researcher really captured the interest of the media with predictions that a large orb-weaving spider, the Jorō spider, was poised to expand its range from its southern stronghold to states further north. Jorō is native to eastern Asia, Japan, China, Korea, and Taiwan. Although it likely arrived in Georgia around 2010 it is now found in Florida, Alabama, Mississippi, the Carolinas, Tennessee, Kentucky, Virginia, West Virginia, Maryland and Ohio. Jorō joins its cousin the golden silk spider, Trichonephila clavipes, as a spider from afar that has established residence in our land.

The underside of the Jorō spider has striking red markings. Image credit: Bob Bellinger

The golden silk spider has been in the US for more than a century, where it occupies parts of Florida, several other southeastern states, and even rarely makes an appearance elsewhere, sometimes as far north as Pennsylvania. The golden silk spider, a native of Central and South America, has remained mostly bottled up in the south likely due to its inability to tolerate cooler temperatures further north. However, a recent study by Dr. Nelsen and colleagues found evidence for abundant suitable habitats in eastern North America and some in western North America that could support the Jorō spider. In southern states, populations of the Jorō expand rapidly once they become established in an area. Jorō also has remarkable talents when it comes to moving great distances. In nature, the typical mode of dispersal of many spiders, including Jorō, is by aerial dispersal of spiderlings. They balloon on strands of silk like Charlotte's babies in the book of the same name. By the way, ballooning likely has given rise to the more spectacular moniker for Jorō, the “parachute spider." No, they really will not rain down on you from airplanes. Long distance transit by Jorō probably depends on human assistance, as both adults and their spawn are good hitchhikers. Jorō may have entered this country as an inseminated and gravid female or as an egg-case stowaway in a cargo container from Asia. Rapid population growth coupled with its ability to be transported inadvertently by humans and naturally by ballooning make range expansion likely. Previous research by scientists Davis and Frick found that Jorō spiders have a higher metabolism, supported by a faster heart rate, and a better ability to tolerate freezing temperatures than their warmth-loving cousin the golden silk spider. These traits, combined with more rapid development, enable Jorō to complete its life cycle rapidly before chilly temperatures bring its seasonal development to an end. This suite of adaptations may enable Jorō to escape the relative warmth of the south and expand its range northward along the eastern seaboard.

The bite of the “venomous” Jorō will be terrible and painful, right? Nah, according to expert Rick Hoebeke, the risks to humans and pets are small due to the puny size of Jorō’s fangs, which are unlikely to pierce our skin. I have visited Jorō’s cousin, the golden silk spider up close and personal in the rainforest of Costa Rica and found the large females to be completely non-aggressive. These spiders are passive hunters that build enormous webs, larger than a meter in diameter, to capture prey snared by silk. For arachnophobes these may be scary, but for arachnophiles these are beautiful spiders which may provide important ecosystem services including biological control of crop pests such as brown marmorated stink bugs or spotted lanternflies, with which they have an ancient association in their native range in Asia. Jorō spiders may be like Hannibal Lecter "having an old friend over for dinner" when they reunite with the stink bug or lanternfly here in the US. Large spiders like these may also become juicy prey items for feathered and non-feathered reptiles.

The large and beautiful Jorō spider poses no known direct threat to humans or pets. Like its cousin from Central and South America, the golden silk, Jorō is here to stay in the United States.  Jorō often becomes the dominant orb weaver in colonized locations. Here is the mystery.  How will Jorō affect indigenous orb weevers like the pretty marbled orb weaver, spotted orb weaver, and my favorite, the black and yellow garden spider, destroyer of stink bugs?  If you spot Jorō in your neighborhood, please report it to iNaturalist.

As with all non-native species that arrive on our shores, it is difficult to predict what impact they will have on our ecosystems but experts suggest that beyond their somewhat scary mien, and maybe giving our indigenous large orb weavers like the black and yellow garden spider, marbled orb weaver, and spotted orb weaver a run for their money. In locations in other parts of the world where Jorō is established, it often becomes the most abundant and dominant orb weaver. What will it mean for our resident spiders and their ecosystems? Only time will tell.

In 2022 when Bug of the Week first talked about the Jorō spider, its presence in the DMV was speculative. But in 2023, several sightings of the Jorō spider were confirmed by iNaturalist in Howard County Maryland. The fascinating part of this story stems from the fact that images clearly show both male and female Jorōs present in the landscape. How did they arrive in Maryland hundreds of miles distant from their southern redoubts? While ballooning is possible, the likelihood of both male and female spiderlings dropping from the sky into the same location and hooking up seems somewhat unlikely. Perhaps a gravid female spider or an egg case hitched a ride from down south and inadvertently arrived in eastern Howard County. The million-dollar questions are, of course, did the Jorō survive the mild winter of 2023-2024 in Maryland and will we see even more of this gorgeous spider this year? Clearly, a road trip to eastern Howard County is in order for the Bug Guy. One final tidbit about Jorō comes from Japanese folklore. Jorō is a shapeshifter known as Jorō-gumo. Jorō-gumo turns into a beautiful woman, seduces men, binds them with silk, and devours them. Yikes! Sounds like a bad date to me.

Acknowledgements

Bug of the Week thanks Rick Hoebeke for identifying Jorō as it arrived in the US and for providing insights into the ways of these large beautiful spiders. We also thank David Coyle and Bob Bellinger for sharing great images and knowledge of Jorō. Fascinating studies entitled “Veni, vidi, vici? Future spread and ecological impacts of a rapidly expanding invasive predator population by David R. Nelsen, Aaron G. Corbit, Angela Chuang, John F. Deitsch, Michael I. Sitvarin and David R. Coyle,  “Physiological evaluation of newly invasive Jorō spiders (Trichonephila clavata) in the southeastern USA compared to their naturalized cousin, Trichonephila clavipes” by Andrew K. Davis and Benjamin L. Frick, “Nephila clavata L Koch, the Joro Spider of East Asia, newly recorded from North America (Araneae: Nephilidae)” by E. Richard Hoebeke, Wesley Huffmaster, and Byron J Freeman, and “The Life Cycle, Habitat and Variation in Selected Web Parameters in the Spider, Nephila clavipes Koch (Araneidae)” by Clovis W. Moore ND provided the inspiration for this story and details surrounding the stars of this episode.

To see other large orb weavers and differentiate them from the Jorō spider, please click on this link: https://resources.ipmcenters.org/view/resource.cfm?rid=27877

To hear more about the Jorō spider and calm your fears about Jorō, please click on this link to watch Jorō guru David Coyle’s take on this spider: https://youtu.be/zhO_bwwg-E4?si=nhd9au-t-HRCmw6b

From the mailbag: What’s that fly? March flies in May – Bibionidae

 

Large eyes of the male March fly provide excellent vision for chasing competitors and selecting mates.

 

This little male March fly piqued the interest of a nature enthusiast and inspired this episode. Image: Bill Miller

A couple weeks ago, a bug aficionado inquired about an unusual, largish fly in his yard. This stranger was none other than a March fly, a member of the bibionid clan some 700 species strong. A few seasons back on a welcomed warm afternoon in April, swarms of March flies bobbed and weaved over the lawn in my backyard. In many parts of the land, March flies seem not to get the email and make their appearance in April or May rather than March, creating an interesting misnomer for these small flies. As a family of insects, March flies include randy Lovebugs, a.k.a Honeymoon bugs, so named for their behavior of remaining intwined in conjugal bliss for long periods of time. Adult flies do not bite or sting, but vast numbers emerging in spring and again in fall are a real nuisance to residents in some of our southern states. In addition to entering homes and bumbling about in the garden, Lovebugs splatter windshields of cars and trucks creating hazardous driving conditions. In some locations they become so numerous that they can clog radiators of cars.

 Since last growing season, March fly larvae have been consuming organic matter in the soil beneath my lawn. These tiny maggots are recyclers helping unlock the nutrients in decomposing plants and returning them to the food web that is my backyard. In late spring they complete development and form pupae which, with the warmth of spring weather, mature as acrobatic flies that emerge from the earth and perform over my zoysia grass. The aerial ballet of March flies consists mostly of males jockeying for position to capture a mate as female March flies emerge from the turf. One fascinating study of male swarming behavior discovered that larger males often occupied flight space nearer the ground where they chased other smaller males away - all the better to intercept nubile females as they rise from the earth. After mating, females return to the soil and lay more than 100 eggs to complete the circle of life.

On warm afternoons in March, April, and May swarms of March flies perform aerial acrobatics over the lawn. It’s all part of the mating game. A big-eyed male rests on a blade of grass before taking off to find a mate. And in southern states it’s easy to see why these flies carry the handle of Lovebugs and Honeymoon bugs. As larvae, they recycle organic matter in the soil while adults help keep our world green by pollinating plants.

March flies like this little beauty help pollinate spring blooming trees and shrubs.

Bobbing, weaving, chasing other males, and intercepting females in flight are facilitated by the large complex eyes of the males. These bulbous eyes are actually divided into dorsal and ventral visual systems with the dorsal eyes gathering information from above and the ventral eyes watching what lies below – truly a case of four eyes. However, clever photographic analysis has shown that the dorsal eyes are the ones used to gage pursuit of other March flies and to differentiate potential mates from potential competing suitors. In addition to being highly entertaining as they swarm in my yard, many March flies are important pollinators of spring blooming plants. Each spring my large holly tree gives forth with blossoms that March flies and a wild menagerie of bees, wasps, and other pollinators find irresistible.    

Acknowledgements

The interesting article “Sexual Dimorphism in the Visual System of Flies: The Free Flight Behaviour of Male Bibionidae (Diptera)” by Jochen Zeil was used as a reference for this episode. We thank Bill Miller for sharing his nice image of a March fly, which inspired this episode.