Wednesday, January 6, 2016

Mosquitoes in Winter

A female Culex tarsalis, a species that overwinters as a diapausing adult.

The following is a guest post from our mosquito ecologist Michael Reiskind. You can find more of his work here.

Well, we finally have winter like weather here in NC. I saw a flying, adult Aedes vexans on December 23rd, but the hard freezes over the last couple of days should eliminate those guys.

Early in my academic career, I remember seeing a talk by a “freelance” mosquito control professional who provided service to New York City during the initial outbreak of West Nile virus, in 1999. I remember him noting the dramatic decline in Culex pipiens the two weeks after he sprayed between October 8-15th. Of course, that may have coincided with the onset of cold weather. As most even casual observers would agree there are no mosquitoes in winter. Right?

Of course, it is not that mosquitoes disappear in winter; just the life stage we love (to hate): biting adults. Just as we don’t see annual plants (say, tomatoes), mosquitoes are still there. But where? And how?

The avoidance of unproductive (and inhospitable) times is widespread among life. Many animals can go into a low metabolism period: hibernation for mammals, and diapause in insects. Insects prepare for this by building up resources, and then by lowering their energy demands to as low as possible.

One of the most fascinating things about diapause in insects, and even in the family of mosquitoes, is the diversity of life-history stages that can diapause. Some mosquitoes diapause as eggs, some as larvae, and some as adults. This suggests a degree of evolutionary flexibility between species, although diapause stage is usually conserved within a species (that is, it is canalized).

One of the other interesting things about diapause are changes in behavior leading up to shutting down for the winter. These include endophily (coming inside buildings), changes in food preferences (for nectar instead of blood), and changes in oviposition behavior. Pretty neat stuff. But also adaptive to the fluctuating conditions mosquitoes encounter across seasons.

Here in North Carolina you won’t find any mosquitoes flying on a cold winter day, but rest assured, they are here, waiting, as eggs in birdbaths, as adults in basements, or as larvae in wet tree holes.

References:
Armbruster, P. and Denlinger, D. Mosquito Diapause. Annual Review of Entomology 59: 73-93.

Monday, January 4, 2016

We're back! And a cold weather reminder

Happy New Year! The PDIC staff hope you and your plants thrive in good health in 2016.

Now that cold weather has arrived, this is a reminder that samples shipped during the winter can suffer cold damage in transit. Consider shipping your sample in an inexpensive foam cooler to protect it from cold. All but the sturdiest coolers should then be placed inside a cardboard box before shipping.

Monday, December 14, 2015

PDIC Holiday Closing Information


The Plant Disease and Insect Clinic will be closed for North Carolina State University Holidays. We will close at noon on December 23, 2015 and reopen on January 4, 2016. Samples with suspected disease problems should be submitted by Friday, December 18 to allow time for culturing organisms if necessary for diagnosis. However, samples will be accepted until we close on December 23.

Our best wishes for a joyous holiday season and for a happy, healthy New Year for you and your plants!

Matt Bertone, Entomologist
Shawn Butler, Diagnostician, vegetables, home landscapes and gardens
Lee Butler, Diagnostician, turf
Charles Hodges, Professor Emeritus and Diagnostician trees, grapes, and brambles
Mike Munster, Diagnostician, commercial ornamentals
Emma Lookabaugh, Graduate student, tomato diagnostician
April Varner, Student lab support
Barbara Shew, Director


Wednesday, November 25, 2015

Tales of the Turkey Tail


Thanks to very successful conservation efforts, you may be lucky enough to see a wild turkey if you take a walk in the woods after your Thanksgiving dinner. But it would not take much luck at all to encounter the turkey tail fungus, Trametes versicolor on your walk. This subtly beautiful fungus probably is the most common wood rotting fungus on dead hardwoods throughout North America (Gilbertson & Ryvarden, North American Polypores, 1987). In fact, you may not need to leave your neighborhood to see turkey tails on old stumps like these flowering cherries we removed a couple of years ago.

New fruiting bodies of the turkey tail fungus Trametes versicolor on a flowing cherry stump

The common name of the turkey tail fungus refers to the semicircular rosettes of varying colors in the fruiting bodies (the spore producing part) of this fungus. The species name versicolor describes both the multicolored bands seen at different times within an individual specimen and the color variations seen among different specimens.
Bands of color variations in an old fruiting body

  T. versicolor can be distinguished from similar species by the tiny pores visible on the underside of the fruiting bodies. Like mushrooms, this fungus belongs to the basidiomycetes, but unlike the button mushrooms you may have had with your Thanksgiving dinner, T. versicolor is a polypore, a basidiomycete that produces spores within pores rather than on gills. Also unlike many mushrooms, the fruiting body is somewhat leathery (not fleshy) and long lived. The fruiting bodies first appeared on our cherry stumps in September and have been expanding and changing color since then.

Small pores covering the lower side of the fruiting body
                             

 Trametes versicolor is one of the white rot fungi, indicating that the fungus can decay lignin, which along with cellulose, is a main component of wood. White rot fungi such as T. versicolor break down the dark lignin in wood, leaving the lighter colored cellulose behind. Other so-called brown rot fungi break down cellulose, leaving behind dark lignin. Many species of both white rot and brown rot fungi cause rots in living trees, but T. versicolor is not a pathogen and decays only nonliving materials. When you gather up piles of leaves and fallen sticks and branches in the fall, you can begin to appreciate that decay organisms such as T. versicolor perform a very necessary function in nature. Without them, we’d soon be inundated with layers and layers of plant debris. In fact, a recent theory proposes that the evolution of white rot fungi brought about the end of the massive accumulation of plant materials characteristic of the coal age.


As you might guess, T. versicolor has been studied for its potential to remove lignin in various industrial processes. It also is has been studied for medicinal purposes and is used in traditional Chinese medicine. Not surprisingly, the dried fruiting bodies have been used as dyes of protein based fibers like wool and silk (Binion et al, Macrofungi Associated with oaks of Eastern North America, 2008). The turkey tail fungus is commonly sold in craft stores for use in seasonal floral arrangements, and if you would like to add a touch of turkey to your Thanksgiving decor, the source may be as close as your own backyard. 

Tuesday, November 24, 2015

Kissing Bugs and Chagas Disease in NC

The causative agent of Chagas disease is a protozoan called Trypanosoma cruzi, seen here at center among human blood cells. Image courtesy of Public Health Image Library (PHIL)/CDC/ Dr. Mae Melvin

News reports out of Texas, and now North Carolina, have been stirring up fears about "deadly" insects and a lesser known, but potentially serious illness: Chagas disease. Most people in the United States have never heard of this malady, yet it affects millions of people every year...in Central and South America.

The vast majority of Chagas disease cases are from rural areas in the New World tropics. Cases in the United States are rare, and most have been diagnosed from people who traveled here from outside the country. In fact there are at present only seven verified cases of natively-infected (termed "autochthonous") Chagas in the United States since 1955, and none of these was from North Carolina (see Reference 2). To put this in perspective, malaria -- a mosquito transmitted protozoan disease often thought of as exotic -- has been recorded as autochthonous 63 times since 1957.

Since I am an entomologist and not a medical pathologist I will not be writing about the disease itself, including its forms of transmission, symptoms and treatment. However, there are many great resources that describe the disease including the Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO), and Wikipedia. I would, however, like to discuss the biology, identification, methods/risks of bites, and prevention in relation to the bugs themselves.

On that note, let's start off with a real kissing bug found right here in NC:

The Eastern blood-sucking conenose (AKA kissing bug), Triatoma sanguisuga, is native to NC and much of the southern and middle U.S.

Kissing bugs are true bugs (Hemiptera) in the family Reduviidae, most of which are referred to as assassin bugs. With ~7,000 species worldwide, the family Reduviidae is among the largest in the order. Most species in the family are predators, feeding on other insects and arthropods. However, the subfamily Triatominae, and the subject of this post, has largely abandoned the predatory lifestyle for one of blood-feeding. These bugs feed on a wide variety of vertebrate hosts, including reptiles, amphibians, birds, and mammals. In all there are over 130 species of kissing bugs, the majority being found in the Western Hemisphere.

Although most species are tropical, kissing bugs are native to North Carolina and have been for as long as humans have been here. At least two species can be found in the state: Triatoma sanguisuga and T. lecticularia. T. sanguisuga is more common, but even it is not frequently encountered. The reasons why they are so rarely found are two-fold. First, they are nocturnal, preferring to hide during the day. They may be seen at lights at night after dispersing (they have wings and can fly) but otherwise it's not often that you will see them in your daily lives. Second, they are often associated with small mammal nests, especially species of Neotoma (woodrats); the Eastern woodrat (Neotoma floridana), for example, can be found in North Carolina where it builds nests out of sticks and other debris. These nests are a perfect habitat for kissing bugs to hide before feeding on the inhabitants. Other mammal hosts of particular importance are opossums (Didelphis virginiana), raccoons (Procyon lotor), and armadillos (Dasypus novemcintus), but they will feed on a variety of mammals including livestock, pets, and humans.

As true bugs, kissing bugs undergo incomplete metamorphosis: after the egg, there are eight nymphal stages (instars) before they become an adult. All free-living stages feed on vertebrate blood, although they have been known to take other insects as food. The name "kissing" bug comes from the fact that when the bugs feed on humans at night, they prefer the face, especially the lips and eyes. Kissing bugs swell greatly when engorged, usually taking 20 minutes or so to feed. Their bites do not initially hurt, so as not to wake their victims, but often become itchy, swollen and painful. The bites can last for weeks and in some cases allergic reactions to the saliva can occur, even resulting in anaphylaxis.

The Chagas disease cycle begins when a bug feeds on an infected host, drinking blood containing the parasites. Many mammals that are fed on by kissing bugs (but not typically birds) can harbor the pathogen that causes the disease, but these animals rarely show symptoms. In fact, researchers at Wake Forest University (North Carolina), found that 1 of 12 (8.3%) opossums and 3 of 20 (15%) raccoons they trapped locally had the parasite. The parasite then grows and multiplies in the bug until it is ready to infect another organism. Unlike mosquitoes and many other blood-sucking arthropods, the disease is not transmitted directly through the bite. Instead, the parasites are found in the feces which may be deposited while feeding or somewhere near the bite. Intense itching causes the person to rub the feces into the eyes, mouth or wound where the parasites can enter the new host to complete the cycle. Thus an important factor for getting the disease is not the bite itself, but the likelihood of the feces getting into open wounds or mucous membranes. In this sense our native kissing bugs are rather courteous and discreet with their excreta -- they most often wait until they leave the host before defecating. This is thought to be the main reason why the disease is not common in the United States despite the bugs, disease and reservoir animals being present. In fact many kissing bugs that are tested for the disease have it, as do local mammals. But humans are not a preferred host and are not typically exposed to the parasite-riddled feces. Thus, the species native to most of the United States are not considered vectors of the disease to humans.

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As far as identification, kissing bugs are like most other Hemiptera in that they have a long, straw-like rostrum used to suck liquids. Therefore, if the insect you have has mandibles or chewing mouthparts, it's not a kissing bug. True bugs will also never have more than five true antennal segments, and never more than three tarsal segments (the parts of the "feet").

Side view of an Eastern conenose kissing bug.
Kissing bugs themselves are around one inch in length when fully grown and somewhat flattened (when not fed). The sides of their abdomen (termed connexivum) and thorax are striped, alternating black and orange/red (sometimes even pink in hue). The legs of kissing bugs are thin compared to most assassin bugs, likely because they do not need to grab prey but instead must be able to move quickly. The name conenose comes from the fact that the front of the head is elongate and the rostrum is long and thin. The antennae are placed well in front of the eyes along the "nose". They also have a prominent spine on the back of the thorax.

Often, other true bugs have similar shapes or markings and can be difficult to tell apart from kissing bugs. The following are NOT kissing bugs:

Other assassin bugs


At well over an inch long, wheel bugs (Arilus cristatus) are our largest assassin bugs. They are very easily recognized by the large cog-shaped crest on the pronotum. They lack red stripes and have a much stronger beak than kissing bugs.
Microtomus purcis is a large, primitive assassin bug species that enjoys hunting under bark, likely for woodroaches (Parcoblatta sp.). The large white patches on the wings and half red hind femora are diagnostic for the species.
Milkweed assassins (Zelus longipes) are medium sized, distinctively red/orange and black assassin bugs with long legs. They are often found out on plants where they wait to capture prey with their sticky forelegs.
Massive front legs and a spiny head are characteristics of spined assassin bugs (Sinea sp.). They are generally smaller than many of the previous assassins (around half an inch) and typically lack bright colors.
Black corsairs (Melanolestes picipes) are often attracted to lights and may specialize in capturing scarab beetles with their large, padded fore legs. Black corsairs are obviously black, but other close relatives, like the genera Rasahus and Sirthenea, can be red/orange or striped. The masked bed bug hunter (Reduvius personatus) is a similarly black species found around homes.
Members of the genus Pselliopus are small, common assassin bugs with distinct rings around their appendages and along the body. This nymph, found crawling around a home, shows the typical orange color of the genus.

Other bugs

Leaf-footed bugs, like this Leptoglossus corculus (Coreidae), are similar to assassin bugs (and thus kissing bugs) but have enlarged hind legs rather than enlarged forelegs. The leaf-like hind legs are also a good trait for distinguishing between the groups, but not all Coreidae have them. These bugs have a long, needle-like rostrum for piercing plants that does not fit in a groove on the underside of the body (as in assassin bugs). 
Stink bugs (Pentatomidae) are another group of true bugs that may be mistaken for kissing bugs, but are generally wider and shield-shaped; they also have a much shorter head that is broadly attached to the thorax (i.e. they lack a distinct neck). Shown here is a rough stink bug (Brochymena sp.), a common plant feeding genus.
Florida predatory stink bugs (Euthyrhynchus floridanus) are brightly colored, metallic cobalt and orange/red bugs. As their name implies, they are predators of other insects.
There are many brown stink bugs, including this Euschistus sp. Some feed on plants, while others are predators. Most have distinct "shoulders" or pointed lateral edges of the thorax.

Now infamous throughout their ever expanding range, brown marmorated stink bugs, or BMSBs (Halyomorpha halys) are native to Asia but were introduced over a decade ago into the northeast of the United States. As plant feeders they can be pests, but are most often pestiferous when they enter homes during the fall and winter in large numbers. Their scent can be strong and their presence annoying. They resemble other brown stink bugs, but are unique in having striped antennae.

If you think you have a kissing bug, this short pictorial key should help you identify similar bugs that may bite. If you are still unsure and would like to have a photograph or specimen identified, please visit our website for information on how to submit such a sample.

Finally, how do you control kissing bugs? In the tropics where the bugs live in large numbers among cracks in mud homes or in thatched roofs (and the threat of disease transmission is high), applying pesticides is a good idea. However, here in North Carolina prevention is the key and applying pesticides is not advised, as there are no definitive sites to apply the pesticides. The following are some strategies that can greatly reduce the chances of kissing bugs entering homes, especially in rural areas where there are more mammal hosts:

  • reduce the amount of debris and vegetation directly around the home; wood and leaf piles, stacked rocks and other habitats that attract rodents can also harbor the bugs
  • repair cracks and gaps in homes; use weather stripping on points of entry like windows and doors and make sure window screens are intact and holes are repaired
  • if you suspect kissing bugs are in your home, inspect cracks and tight spaces, especially in bedrooms
  • lights will sometimes attract kissing bugs; minimizing the amount of lights on at night will help to "cloak" homes

Although these preventative measures will help reduce the chances of coming into contact with kissing bugs, in reality it is very unlikely you would ever come into contact with one of these insects anyway. In fact I have never seen one myself in the wild, even after 15 years of living in the state. Of course that is anecdotal, but I think most entomologists in the area would agree that they are uncommonly encountered.

So in conclusion, yes these bugs can carry a deadly disease. But here in the United States, especially North Carolina, you have almost no chance of contracting the disease from these native bugs.

References:
  1. Kissing Bugs in the United States
  2. Trypanosoma cruzi and Chagas' Disease in the United States
  3. Triatominae at Bugguide.net
  4. The Eastern Blood-Sucking Conenose, UFL

Friday, September 4, 2015

Boxwood Blight Active Again

After a lull of several months, samples of suspected boxwood blight have been coming to the NCSU Plant Disease and Insect Clinic (PDIC) over the course of the last month. Just this week we’ve had confirmation on samples from a garden center in Macon County, North Carolina, and home landscapes in Transylvania, Jackson, and Forsyth Counties.
Symptoms of boxwood blight at a garden center. Photo: Alan Durden, NCCES

This news is disheartening for two reasons. First of all, the find in Winston-Salem follows concerted efforts to stamp out the 2013 outbreak there. Secondly, the other confirmations this week represent the first reports of boxwood blight in our southern mountain counties of North Carolina.

Landscapers, homeowners, nurseries, and garden centers should be alert for symptoms of boxwood blight: brown leaf spots, black streaks on green twigs, and leaf drop, usually starting in the lower portions of the plant. As we move toward the holiday season, individuals and businesses that cut boxwood tips for wreaths and other greenery should be sure they understand the implications of this disease for their industry.
Leaf spots, stem streaks, and defoliation typical of boxwood blight.

Comprehensive sets of recommendations are available from the Virginia Boxwood Blight Task Force. Those publications mention Virginia’s “Boxwood Blight Cleanliness Program”. The equivalent for North Carolina is the NC Department of Agriculture and Consumer Services, Plant Industry Division, Plant Protection Section's Boxwood Blight Compliance Program for nurseries.

It is still the policy of the PDIC that samples submitted by nurseries for boxwood blight confirmation only will be processed at no charge; however, we recommend submitting them through the NC Cooperative Extension Service or the NCDA&CS.

Thursday, August 27, 2015

Are Asian or Japanese giant hornets in the United States?

No.

But there is a lot of fear of them. It could be from news reports out of China stating death tolls in the dozens, or natural history videos depicting them massacring thousands of honey bees. They certainly are vicious insects with an aggressive reputation, but plaguing North Carolinians (or other Americans)? It's not happening.

Here's a little background on these wasps. The family Vespidae has a large diversity of forms and social structures and is found throughout the world. Many species are solitary, preferring to work alone to provide nests and food for their young - food typically being other insects (as in the Eumeninae; see image below left) or pollen (as in the Masarinae). The familiar paper wasps make up the subfamily Polistinae (see image below right), and are social but usually have small to moderate-sized colonies. Many build open nests out of paper made by gathering pulp from dried wood. They are often seen under the eaves of homes in our area and, while they can be aggressive, are often tolerant of people. They are also beneficial predators of many garden pests.


Potter wasps (left) and paper wasps (right) are two familiar groups in the family Vespidae. Note how members of this family fold their wings lengthwise at rest. Photos by Matt Bertone.

The subfamily Vespinae encompasses species with the largest colonies (numbering in the hundreds to over one thousand individuals) and contains the subject of this article. Some are small wasps that typically build paper nests in the ground, including the well-known yellowjackets (Vespula spp.; see image below). Others, generally called hornets, build large paper nests in the open or inside dead trees, attics or other hollow structures. Hornets and yellow-jackets are highly aggressive toward perceived threats and, thus, have a bad reputation. Among the vespines, the largest wasps are in the genus Vespa. This genus has 23 species native to Europe, the Middle East, NE Africa, and Asia (most diverse in SE Asia); there are no native Vespa in the Western Hemisphere. Like many other members of the subfamily, the adult wasps will hunt and dismember prey (even scavenging carrion) to feed to their young, while taking sugary meals of ripe fruit or oozing tree sap for their own energy.

Yellowjackets (like this Vespula maculifrons du Buysson) are small to medium wasps that typically create nests under ground. Note the notched eye, characteristic of Vespidae. Photo by Matt Bertone.

The largest are Asian giant hornets (Vespa mandarinia Smith; see image below) also called yak-killer hornets and including a subspecies called the Japanese giant hornet (V. mandarinia japonica). Workers average about 3.5 cm, but queens can be a whopping 5.5 cm with a 7 cm wingspan! These wasps, as alluded to above, are very aggressive and pack large quantities of potent venom. While the LD50 of V. mandarinia is 4.0 mg/kg (on par with the toxicity of some venomous snakes), it is actually less toxic by volume than our native southeastern yellowjacket, Vespula squamosa (Drury), with an LD50 of 3.5 mg/kg. However, the volume of venom injected and some necrotic and hemorrhagic properties of the venom make this hornet dangerous. The biology of Vespa mandarinia, especially related to their attacks on honey bees, was outlined thoroughly by Matsuura and Sakagami (1973).

The Asian giant hornet (Vespa mandarinia) is a large wasp found in many parts of middle and southern mainland Asia and nearby islands. This specimen measures just over 3.5 cm (not including the stinger), and in life would have a vibrant yellow/orange head and stripes on a dark brown or black background. Note that the eyes are very far from the back of the head, almost twice the distance as the width of each eye - a characteristic of this species. Photo by Matt Bertone.

So what are people seeing when they think one of these monster killer hornets is on the loose? There are two main suspects found in the Eastern US that are often confused for Asian giant hornets. The first is actually a close relative, the European hornet (Vespa crabro L.; see images below). This species was introduced from Europe/Asia into the US sometime in the 1800s and first recorded in NY. It has since spread across much of the eastern half of the US. These wasps tend to nest in tree cavities and prefer to be away from humans, but sometimes are found in other situations, even in attics or walls of homes. They can be aggressive and have painful stings, but are not usually an issue to homeowners.

In life, European hornets (Vespa crabro) have a mix of yellow, black and reddish-brown colors.
European hornets (Vespa crabro) have a much darker head with larger eyes than Asian giant hornets. They also have wider yellow stripes with black markings on their abdomen. This specimen is about 3.0 cm in length. Photo by Matt Bertone.

Another candidate, and a wasp that is even larger than any hornet we have here, is the Eastern cicada killer (Sphecius speciosus (Drury)). These wasps are distantly related to hornets. They are in fact a type of solitary hunting wasp in the family Crabronidae (formerly a part of Sphecidae, which contains familiar wasps like mud daubers). As their name implies, cicada killer wasps hunt cicadas. In mid-summer, males guard plots of ground suitable for tunnels and may "attack" any intruder, especially other males. However, they cannot sting. It's the females that find this prey and paralyze it, not for her own food but for her young (larvae) to consume. Once a female has paralyzed her cicada, she buries it in the ground and lays an egg that will hatch into a larva that will consume the prey. Although they have an impressive stinger and have venom, they are not aggressive and prefer to avoid conflict - after all there is no one to do the work if they die! If you can get them to sting (which would take a lot) they apparently cause very mild pain, especially for their size.

Eastern cicada killers (Sphecius speciosus) prefer to be hunting cicadas or digging in the ground than swarming or attacking. They are solitary by definition, but sometimes nest in large aggregations, somewhat like an apartment building. Note the large, unnotched eyes and wings that are not folded lengthwise at rest.
The Eastern cicada killer wasp (Sphecius speciosus) is an impressive insect. It has to be, though: females must attack and wrestle down cicadas to paralyze and bury for their young. Note the large, round eyes with no notch and elongate, pointed abdomen. Photo by Matt Bertone.

In conclusion, although you may see a large and scary wasp out and about, the likelihood of it being an invasive Asian giant hornet is zero. The two giant wasps we have are impressive, but not very surprising or dangerous (basically harmless in the case of cicada killers). Finally, for comparison, here is a photo of all three next to each other:

Three giant wasps, the first of which you will not see in the US: A) Asian giant hornet (Vespa mandarinia), B) European hornet (Vespa crabro), C) cicada killer (Sphecius speciosus). Photo by Matt Bertone.

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One final thought: despite lacking "killer" Asian giant hornets, every year dozens of people in the US die from wasp stings (including those from honey bees, Apis mellifera L.). These are largely attributed to allergic reactions, but in some rare cases that involve extremely large numbers of stings, the venom itself can have lethal effects. It is always good to be careful around any stinging insect, especially those that live in large colonies that might be vigorously defended. People who are allergic should always have an epinephrine autoinjector ready when working around such insects. If you have a large wasp nest that appears too difficult to control, it is best to hire a professional to take care of the nest. For more information on control of these wasps, see this note on Dolichovespula and Vespula, and this note on Vespa crabro.


Helpful resources:

Friday, June 5, 2015

A Rope of Maggots

- Science, 1894

Dark-winged fungus gnat larvae are worm-like creatures, each translucent white with a black head and not a single leg on their body. They usually squirm their way around alone or in small gangs, in wet leaf litter, rotten logs, compost bins, potting soil and, of course, fungi. They feed on decaying materials in hopes of someday becoming a winged fly, ready to mate and make more larvae.

The black head is all that keeps this fungus gnat larva from resembling a true worm.

But when conditions are right (or maybe wrong for the larvae) they become something more.
They become snakeworms. Army worms*. A rope of maggots:

A mass of fungus gnat larvae (Sciaridae) from Craven Co., NC (Photo: Thomas Glasgow)

It's hard to judge the oddity from afar, because it just looks like a giant worm or snake. But closer up you can see that this pulsing mass is made up of hundreds or even thousands of these young fungus gnats:

Close up of the mass. (Photo: Thomas Glasgow)

Photos don't really do the mass justice, especially because of the way it moves. To get a good idea of the motion of this ocean [of maggots], just watch this video (be warned: it's not for the squeamish). These masses can attain many feet in length. Sometimes the group splits; other times groups fuse. In a display of futility, the "head" sometimes even follows the tail, the whole unit creating a writhing merry-go-round.

At this point you are probably asking WHY are these critters doing this? Well, nobody really knows. The phenomenon is recorded from all major continents and displayed by many species. In Europe, for example, Sciara militaris is well known and named for its behavior of marching in ranks. These gregarious larvae seem to grow in unison and then migrate together. If I had to guess, I would say that they are going together to a site for either better food or to pupate. I also imagine that alone they would quickly dry out or be eaten, but these convoys allow the larvae to move more efficiently and in a safer (and moister) manner. Whether this occurs normally depending on the species, or it is simply an opportunistic behavior determined by certain abiotic factors, I am not sure. But I have even seen photos where larger maggots of other flies travel with these gnats, which means it's not only the fungus gnats who think it's a good idea.

Although disturbing, these masses are harmless and merely an interesting survival strategy. Once safe and left to pupate, the larvae may turn into small drab flies or into the more impressive orange and black sciarids seen here:

Mating pair of Odontosciara nigra (male left; female right), a conspicuously large and colorful early summer species here in North Carolina.

Let's just hope they don't skip right to becoming giant militaristic, worm creatures with armor plates and pulse cannons.



* not to be confused with armyworm caterpillars (Lepidoptera: Noctuidae)

UPDATE: Debbie Roos has a nice blog post about these fungus gnat larvae (which can be pests in greenhouses) that shows a mass with another type of maggot tagging along.