As spiders leave the kitchen, pests keep cooking

A spider in the family Anyphaenidae has made its home on a twig infested with scale insects.  Photo: Emily Meineke, Harvard University

I think by now most people accept that we can’t hope to preserve all extant creatures over the next 50 or 100 years. Global changes in temperature and habitat will help some species and hurt others, as Elsa Youngsteadt showed in her recent paper. Since we can’t save every creature, what is really important to protect? Increasingly, people try to understand and protect species and ecological interactions that generate ecosystem services for people, rather than diversity per se.

Former undergraduate researcher Anna Holmquist examines branches in the field. Photo: Emily Meineke, Harvard University

Urban warming makes street tree temperatures similar to what is expected under climate change, so we have studied them to predict the effects of warming – urban and global – on pest abundance and tree health. Street trees also host a surprising amount of arthropod diversity if you just look hard enough. In a new paper, our former graduate and undergraduate students, Emily Meineke and Anna Holmquist, with help from Gina Wimp at GWU, studied the effects of warming on spider communities in street tree canopies.

The team tested two predictions. Spiders like to eat and often become more abundant in places where prey is more abundant. So we predicted that, since heat increases herbivore abundance, spider abundance would follow. However, because some spiders probably benefit from warming while others do not, we predicted the composition (member species) of the spider community would be different in hot and cool trees.

The fitness of this spider probably increases with warming since it is hot and sweaty from exercise and yoga. Other spiders (not pictured, you can only work kids so hard) die in, or leave, hot places. Thus, yoga spiders will be more common on hot trees and the community composition will change. Artwork by: I.F.

Ghost spiders, like this one, are nondescript but perform important ecosystem functions. Photo: Matt Bertone, NCSU.

Spiders were by far the most abundant natural enemy group. However, as herbivore abundance increased with warming, spider abundance stayed the same. This is bad news for trees because it means that herbivores can increase unchecked. Instead, urban warming altered spider community structure due in part to a whole family of spiders, Anyphaenids — aptly named ghost spiders – virtually disappearing from the hottest trees in one year of the study. This is bad news for conserving urban biodiversity and also because ghost spiders feed on particular pests like lace bugs.

In this experiment, warming reduced biodiversity but also likely reduces biological control by predators, an important ecosystem service. Something happens in these trees to make a common ecological interaction – predators congregating to prey – stop happening. The consequence is that pests go nuts and trees suffer.

Read the full paper here:
Meineke, E.K., Holmquist, A.J., Wimp, G.M., Frank, S.D. (2017) Changes in spider community composition are associated with urban temperature, not herbivore abundance. Journal of Urban Ecology, 3 (1): juw010. doi: 10.1093/jue/juw010.

January 26th, 2017|Categories: Feature, Natural Enemies, Urban Ecology|Tags: , , , |

Cicada Killer Wasps Are on the Wing

This is a guest post by our Research Associate Elsa Youngsteadt

A male cicada killer perches atop a retaining wall, keeping watch over his territory. (Photo: E. Youngsteadt)

A male cicada killer perches atop a retaining wall, keeping watch over his territory. (Photo: E. Youngsteadt)

North Carolina’s steamy July days bring out some of our most spectacular solitary wasps. These sleek and streamlined hunters are quite docile toward humans, but are to be feared by other insects and spiders. The largest of these wasps in North Carolina is the cicada killer (Sphecius speciosus). Females can be up to an inch and a half long and weigh about a gram—as much as a shelled almond.

Cicada killers are solitary, meaning that each female typically builds her own nest and hunts prey to feed her own offspring. (In this habit, they differ from yellowjackets, hornets, and paper wasps, which live in social colonies.) Nevertheless, cicada killers do tend to be found in groups, since they all agree on what makes a good nesting area: sparsely vegetated, southeast-facing slopes or unmortared retaining walls, with plentiful cicadas in nearby deciduous trees.

NC State’s campus hosts a few such cicada-killer neighborhoods, and we started to see the wasps out and about last week. But they haven’t quite gotten around to killing cicadas yet.

Although individual cicada killers have unique markings, they differ from other, similar species in size, body shape, and overall color pattern. (Photo: E. Youngsteadt)

Although individual cicada killers have unique markings, they differ from other, similar species in size, body shape, and overall color pattern. (Photo: E. Youngsteadt)

Males emerge a week or two before females, and spend their time feeding at flowers or sap and establishing territories, where they perch on vegetation or stones to keep watch. They make sorties to chase off other males, pursue females, and investigate intruders—including you, your pet, or your camera lens. Once you know that males cannot sting, these hovering advances (described by one pair of biologists as “businesslike”) can seem quite charming.

This male thoroughly investigated me and my camera before settling down for a photo shoot. (Photo: E. Youngsteadt)

This male thoroughly investigated me and my camera before settling down for a photo shoot. (Photo: E. Youngsteadt)

When the females finally emerge, they mate—only once, but for a long time (30 to 50 minutes). When they settle on a good spot for a nest, the earth-moving begins, and herein lies the occasional conflict between cicada killers and humans. One female wasp can excavate nearly a half-gallon of soil for a single burrow, which can be up to 40 inches long! And she makes about four burrows in her lifetime. She piles the tailings in a neat but largeish U-shaped mound at the entrance of each burrow, and this pileup can damage turf and other plants. But keep reading.

Cicada killers also benefit trees by hunting large insect herbivores—namely, dog-day cicadas in the genus Tibicen. These are the camo-colored, thumb-sized insects that spend their brief adult lives in July and August shrieking and buzzing in the treetops or sawing into branches to lay their eggs.

In her lifetime, one female cicada killer can gather 100 or more cicadas (a hundred!)–each of which weighs about twice as much as she does. She paralyzes the cicada with her stinger and hauls it laboriously back to her nest. She brings one cicada for each of her male offspring, and two or three for each female. (The wasp knows in advance the sex of the next egg she will lay, and stocks the nest accordingly). Then she lays an egg at the base of the cicada’s middle leg and seals up the nest chamber that contains it, never to meet her offspring.

The eggs hatch in a day or two and the long-necked larvae develop quickly, each one polishing off a whole cicada in less than four days. Upon completing its meal, the larva spins a silken cocoon and enters diapause, remaining in a suspended state until the following May or June, when it pupates. That brings us back to the present season, when adult wasps emerge and dig their way out of their nursery tunnels in July—males first.

Entrance to a cicada killer burrow between stones in a retaining wall. (Photo: E. Youngsteadt)

Entrance to a cicada killer burrow between stones in a retaining wall. (Photo: E. Youngsteadt)

If you have cicada killers on your property and find that you really can’t endure them, despite their docile manner and benefits for trees, there are few proven options for control. One study in West Virginia eliminated cicada killer activity on a golf course by spraying the appropriate insecticide directly into active burrows, or immediately around their entrances. (Broader area sprays were not particularly effective.)

However, because the developing larvae may survive this treatment, and because good nesting habitat remains appealing to new females year after year, wasp removal will likely be an annual battle. In most situations, the benefits controlling cicada killers with insecticides are unlikely outweigh the financial and environmental costs.

Other wasp biologists have recommended fertilizing and liming the soil in the affected area to promote thicker vegetation that will eventually deter the wasps; one has informally demonstrated a laborious but effective control method that involves plugging burrows and using a badminton racket to swat the wasps. (Again, this would be an annual undertaking.)

I hope that you don’t have to go to all that trouble, and that you can enjoy watching these insects, instead. And stay tuned for updates on our campus wasps. Once we find females dragging cicadas to their nests, there will be another photo shoot!

Sources and further reading:

Dambach, Charles A., and Eugene E. Good. 1943. Life history and habits of the cicada killer in Ohio. The Ohio Journal of Science, 43: 32 – 41.

Evans, Howard E., and Kevin M. O’Neill. 2009. The Sand Wasps: Natural History and Behavior. Harvard University Press. pp 37 – 43.

Hastings, Jon M., et al. 2010. Size-specific provisioning by cicada killers, Sphecius speciosus, (Hymenoptera: Crabronidae) in North Florida. Florida Entomologist 93: 412 – 421.

Holliday, C. W., and J. R. Coelho. Improved key to new world species of Sphecius (Hymenoptera: Crabronidae). Annals of the Entomological Society of America 99: 793 – 798.

Weaver, Joseph E. 1995. Life history, habits, and control of the cicada killer wasp in West Virginia. West Virginia University Agricultural and Forestry Experiment Station, Circular 161.

There is also a wealth of information, videos, and ideas for controlling cicada killers at the websites of biologists Chuck Holliday and Joel Coelho.

July 20th, 2015|Categories: Feature, Natural History and Scientific Adventures, Urban Ecology|Tags: |

Bagworms hatching…scout conifers or other plants with weird ‘pine cones’

If you have conifers or other plants that seem to have grown weird, dangling pinecones, look again because you have bagworms. Bagworms have been hatching for the last week or so. You can find the tiny caterpillars with tiny upright bags anywhere there are bags left from last year.

First instar bagworms with tiny upright bags. Photo: AG Dale

First instar bagworms with tiny upright bags. Photo: AG Dale

The Bagworm, Thyridopteryx ephemeraeformis, is a very common pest of conifers and other ornamental plants throughout the eastern United States. These pests overwinter as eggs within the mother’s bag. Larvae emerge from the bag during the May and June (depending on location and temperature). The larvae crawl or drift via silk strands to nearby foliage where they begin to feed. Bagworms are relatively sedentary during their lifetime, most often remaining on the same tree until they pupate. Adult females are wingless and never leave the tree. Male bagworms develop into a small brown moth.

Large bagworm feeding on maple. Photo: SD Frank

Bagworms feed on plant foliage and heavy infestations can defoliate trees and shrubs. Young caterpillars produce a silk bag on their posterior end that gradually collects plant debris. This creates a bag covered in pine needles or leaves that protects them from predators and looks (sort of) like a pinecone. Since they don’t move much as larvae and the females don’t fly, they can build up dense populations. Since they are so camouflaged and protected from insecticides, management of these insects can be difficult and time consuming. One of the most effective, yet time consuming methods of treatment are hand-picking or cutting the female pupae bags off of the branches. When this is impractical or impossible, there are chemical control options available that should be applied when caterpillars are young (now) because they are more vulnerable. As with many other pest insects, bagworms are susceptible to predation from parasitoids and birds which can also assist in their control.

PhD student Adam Dale contributed to this post.

May 21st, 2015|Categories: Feature, Landscape IPM|Tags: , , |

Gloomy scale crawlers are active and vulnerable

Adult gloomy scale. Photo: SD Frank

Adult gloomy scale. Photo: SD Frank

Gloomy scale, Melanaspis tenebricosa, is an armored scale that feeds on maples and other tree species. It becomes very abundant on red maples on streets and in landscapes and can cause branch dieback and tree death in some cases. It is not unusual to find trees with nearly 100% of their trunk covered in scale. Street trees are particularly prone to gloomy scale. Crawlers of this scale are active now and can be seen on bark and under scale covers. One of the reasons we have found this to be such a pest is that female gloomy scales produce about 3 times as many eggs when they live on relatively warm trees (like in a parking lot) than when they live on cooler trees (like in a shady yard). This amazing work is outlined in a recent paper by Adam Dale.

Control of this scale is complicated because crawlers emerge over 6-8 weeks so it is impossible to treat all the crawlers at once with horticultural oil or other contact insecticide. This is different than in other scales, such as euonymus scale, in which all crawlers are produced within a narrow window of 2 weeks or so. Adam Dale took a video of some gloomy scale crawlers so you can get an idea of how tiny and nondescript they are. This may also give you an idea of why scales are so vulnerable at this stage to the environment, predators, and insecticides like horticultural oil. Once they produce their thick waxy cover they are much less vulnerable to all these factors.

May 21st, 2015|Categories: Feature, Landscape IPM, Urban Ecology|Tags: , , , , |

Cottony Fluff on Trees and Shrubs – Felt Scales

Oak eriococcid scales on a willow oak twig. Photo: AG Dale

Eriococcidae is a family of scale insects commonly called ‘felt scales’. This is a different family than the common soft scales (Coccidae) that includes species like wax scale, lecanium scale, terrapin scale, and cottony maple leaf scale. Felt scales look a lot like mealybugs. The one that is most abundant now is the oak eriococcid scale. If you look at many urban willow oaks this time of year you will see small cottony fluffs, like Q-tips,  on the bark, twigs, and branches. In some cases they become extremely abundant.

This is not a well-studied group of scales. Not much is known about their biology or management.

This is the underside of an oak eriococcid scale. Notice the orange eggs building up toward the back of her body. Photo: AG Dale

This is the underside of an oak eriococcid scale. Notice the orange eggs building up toward the back of her body. Photo: AG Dale

The oak eriococcids have one generation per year. The cottony sack you see now is the ovisac (egg sack). If you dig around in the cottony material you will see tiny yellowish eggs. Pretty soon crawlers will emerge from the cottony mass to find a spot to settle and feed. They also produce honeydew so these are some of the scales responsible for the tiny drops on your windshield if you park under willow oaks or other infested species. Heavily infested trees like some on campus make the sidewalk black with sooty mold.

Other felt scales of importance are the azalea bark scale, European elm scale, and the new crape myrtle bark scale. Control of felt scales has also not been studied well. However, like their aphid and mealybug relatives, imidacloprid and other neonicotinoids should provide some control. If you watch for the crawlers (soon!) you could make a dent with horticultural oil. The oak eriococcid sscales are one of the earliest scales to produce eggs in Raleigh. They are harbingers of all the other scale crawlers to come.

April 2nd, 2015|Categories: Feature, Landscape IPM, Urban Ecology|Tags: , |

Emerald Ash Borer in Wayne Co. North Carolina – Quarantine Implemented

David Cappaert, Michigan State University

Emerald ash borer has been present in North Carolina since June 2013. Granville, Person, Vance and Warren counties have been under EAB quarantine since then. Now EAB has been found at the Cherry Hill Research Facility in Goldsboro, NC. You can read the NCDA&CS press release here. Emerald ash borer is a very destructive exotic pest that has killed millions of ash trees in the Midwest, mid-Atlantic, and other regions.

EAB exit hole. Photo: Pennsylvania Department of Conservation and Natural Resources - Forestry Archive

EAB exit hole. Photo: Pennsylvania Department of Conservation and Natural Resources – Forestry Archive

If you notice ash trees with canopy dieback, sucker growth, or general decline inspect the trees for D-shaped exit holes. You can remove bark to look for larvae and serpentine galleries. Comprehensive biology and management information is provided by a consortium of universities at http://www.emeraldashborer.info.

Home and landowners are encouraged to report any symptomatic activity in ash trees to the NCDA&CS Plant Industry Division hotline at 1-800-206-9333 or by email at newpest@ncagr.gov. The pest can affect any of the four types of ash trees grown in the state.

EAB Larvae. Photo: David Cappaert, Michigan State University

EAB Larvae. Photo: David Cappaert, Michigan State University

March 31st, 2015|Categories: Feature, Landscape IPM, Urban Ecology|Tags: , |

Clumsy native bees benefit you and me

This guest blog is by April Hamblin, an M.Sc. student conducting research on urban bees in our lab.

What comes to mind when you think of bees and pollination? Most people immediately think of honey bees and bumble bees, but forget the native bees that inhabit the many natural and urban landscapes around us. In fact, there are more than 500 species of native bees in North Carolina alone.

A great deal of research has shown that these wild bees actually pollinate better than the managed, exotic honey bee. Why is this, you ask? It turns out that the native bees are less efficient than honey bees at holding on to all of the pollen grains they collect, which allows for more efficient pollination as it falls from their bodies. This is great for the plants themselves and anyone that likes to eat plants and their products. Native bees have also been shown to continue foraging in not-so-ideal-bee weather, such as cloudy days, when honey bees like to stay inside their hives.

Apis mellifera

Honey bee (Apis mellifera). Photo: Laura Daly

Melissodes bimaculata

Native bee (Melissodes bimaculata). Photo: Laura Daly

 

On the left is a honey bee (Apis mellifera) and on the right, a native bee (Melissodes bimaculata). The bright yellow dots you see on the bees are pollen. What you may notice is that the honey bee keeps most of its pollen neatly packaged on its hind leg in a specialized pollen carrying basket called the corbicula. In contrast, the wild Melissodes bimiculata uses nearly its entire body to collect pollen. In bee species other than the honey bee, any body part modified to carry pollen is called the scopa.

Here is a good way to think about the difference between these two pollen-carrying systems, and the resulting differences in pollination efficiency. Imagine you were trying to carry four boxes of donuts to your co-workers in the morning. Carrying the boxes neatly stacked in your arms would be the honey bee method. If you were using the native bee method, you’d hold them with your arms and feet, try to balance some on your head and back, maybe even a shoulder–and guess what? You’d drop lots of donuts. It is the same for the native bees that carry pollen in many different places–lots of it falls off as they visit new plants, making them excellent (if slightly clumsy) pollinators.

March 31st, 2015|Categories: Feature, Natural History and Scientific Adventures, Pollinators, Urban Ecology|Tags: |

Ambrosia beetle traps are filling up

The granulate ambrosia beetle, Xylosandrus crassiusculus, is the primary ambrosia beetle pest of nurseries in the Southeast. Today we found a similar ambrosia beetle species – the first of the season – in our traps at the NCSU Lake Wheeler Research Station in Raleigh.

Xyleborinus saxeseni. Photo: Pest and Diseases Image Library, Bugwood.org

Xyleborinus saxeseni. Photo: Pest and Diseases Image Library, Bugwood.org

The beetle we found was Xyleborinus saxeseni which is commonly called the fruit tree pinhole borer. This species is also a pest of nursery trees and usually becomes active before granulate ambrosia beetles. However, with the warm weather we’ve had the full suite of ambrosia beetles will be out soon. It is time to protect trees if you haven’t started already. Spray susceptible trees with permethrin every three weeks or so. Ambrosia beetles damage many deciduous tree species and prefer dogwood, redbud, styrax, magnolia, cherry, Japanese maple, and others. You can find more in a free nursery production guide (available as an iBook) and in an article I wrote for American Nurseryman. Although it is time to spray (at least in Raleigh) it is not time for irrigation. We have found that over-watering makes trees more susceptible to ambrosia beetle attacks.

March 12th, 2015|Categories: Feature, Landscape IPM, Nursery IPM|Tags: , , |

Ants eat your crumbs. What’s the fuss?

This is a post by our Research Associate Elsa Youngsteadt about her new paper in Global Change Biology.

The first time we came back to an empty cage in Highbridge Park, I thought there was a problem.

This was a cage cobbled together out of a fry basket from a restaurant supply store plus a square of hardware cloth, and it was firmly tacked to the ground with landscape staples. With its snug, quarter-inch mesh, it should let most insects move freely, while keeping vertebrates out. With holes any bigger than a quarter-inch, mice could squirm through.

Exclusion cage made from a fry basket to keep food scraps safe from rats. Photo: EK Youngsteadt

Exclusion cage made from a fry basket to keep food scraps safe from rats. Photo: EK Youngsteadt

And they would want to, because the cage held a chunk of Nilla Wafer, a Ruffles Original potato chip, and a slice of Oscar Meyer turkey frank. Yum.

The purpose of the cage was to let us measure how much arthropods* alone were capable of eating in this Manhattan park, without interference from mice, rats, sparrows, and whatever other urban critters might shuffle by with the munchies.

(*Arthropods meaning “bugs,” like sowbugs, mites, millipedes, and insects—including ants.)

So I was dubious when we found an empty cage in Highbridge Park on the first day of our study. Could bugs alone have eaten our little pile of food in a day? When we did a trial run back home on the NC State campus, the food never disappeared completely like that. Had a mouse gotten in after all? Had a human passer-by toyed with our experiment?

So we tried again. We moved our setup to a new spot nearby, tucking it discreetly among the trees and undergrowth behind the ball field. We fortified the cage until it bristled with cable ties and landscape pins. And came back a day later.

This time, our arrival was timely. The cage was surrounded by a silent, busy swarm of pavement ants, trundling off the last fragments of potato chip, the last few cookie crumbs. Ants. Not mice, not tampering humans; ants.

This was a scene we would see over and over in the next several days. And maybe we shouldn’t have been surprised.

Ants feasting on hotdog, chip, and cookie in the cage. Photo: EK Youngsteadt

Ants feasting on hotdog, chip, and cookie in the cage. Photo: EK Youngsteadt

After all, ants are notorious visitors to kitchens and picnics, and they are incredibly important scavengers and hunters in natural habitats all over the world (except Antarctica).

But it seems that I’m not the only one impressed by our tiny urban neighbors. Our study of garbage-eating ants was published today in Global Change Biology, and The New York Times, The Washington Post, National Geographic, and Wired have already published their versions of the story. More news in the works from Germany to South Korea, and I’ve described our study to more than a dozen reporters this week.

This process has been delightful and a little exhausting and even puzzling. I mean, sure, I was surprised when ants cleaned up the food the first time—but everybody else is amazed, too? It’s news that ants eat crumbs?

Or is it news that some scientists were nutty enough to weigh hot dogs and potato chips and set them out in experiments around the most densely populated city in the US–in Central Park, in the middle of Broadway, in view of the Statue of Liberty?

Or is it news that ants are competing with rats for this junk we drop? That this little drama plays out over the crumbs to which we never gave a second thought?

I’ll let you decide. Here’s what we found—the bullet-point version:

  1. Bugs in street medians ate two to three times more junk food than those in parks.
    Co-author Ryanna Henderson sampling a median. Photo: EK Youngsteadt

    Co-author Ryanna Henderson sampling a median. Photo: EK Youngsteadt

    Street medians are little strips of trees and groundcover planted between lanes of traffic, and they host fewer ant species than do parks. Ecological theory predicts that more diverse ecosystems are more efficient, so we were surprised that bugs in medians ate more than those in parks. We indulged in some extrapolation and calculated that the bugs inhabiting the 150 city blocks of medians on Broadway and West Street are capable of eating more than a ton of food per year–the equivalent of 60,000 hot dogs.

  1. Pavement ants (Tetramorium species E) are big eaters. We didn’t watch our cages for 24 hours to see exactly which species collected how many crumbs—but at sites where we found pavement ants, more got eaten. Pavement ants originated in southern Europe and the Middle East, but have been living in American cities for more than a century. They love nesting near pavement, so they’re more common in medians than in parks. (But Highbridge Park had them, explaining its big, median-like appetite.)
  1. Bugs compete with vertebrates (rats!) for our food garbage. Alongside our cages, we offered a second set of uncaged foods, available not only to bugs but also to any hungry vertebrate. More food got eaten from this open treatment than from the cage. That means that both groups of animals (bugs and vertebrates) want the stuff we drop. In other words, they compete for it; what one group gets, the other group doesn’t. I would love to know how much of that uncaged food went to ants and how much to rats–and whether that depended on the kind of food, the size of the food, the time of day, the habitat… But those are goodies for another study someday.
  1. Hurricane Sandy was a disaster, but not for garbage-eating bugs. Several of our study sites were inundated with saltwater during Hurricane Sandy, seven months before our study. We thought this would matter to the wildlife. But we detected no effect of flooding on how much food got eaten. Maybe there was still an effect on some kinds of bugs—we’re still figuring that out—but certainly not on those that eat our crumbs.

 

I admit I’ve often tossed an apple core into the woods, not even thinking of it as litter. It’s “biodegradable,” so it doesn’t count, right? Now, my friends, we have met our urban biodegraders. To them it counts, and their work behind the scenes is making our garbage disappear.

Comic by Dorit Eliyahu  https://sites.google.com/site/doriteliyahu/home

Comic by Dorit Eliyahu
https://sites.google.com/site/doriteliyahu/home

December 2nd, 2014|Categories: Feature, Lab Happenings, Natural History and Scientific Adventures, Urban Ecology|Tags: , |

Do scary parasites mean my yard is healthy?

This is a post by our Research Associate Elsa Youngsteadt about some rare parasites she found.

In a lab full of people quietly staring through microscopes, a startled yelp occasionally breaks the silence. And I admit, it sometimes comes from me. Diving into the magnified world can be a lot like watching a scary movie on a big screen.

Usually the freak-out happens when I’m doing something soothingly monotonous, like counting tiny scale insects on leaves. I get in a groove and forget that I’m seeing everything 30 times bigger than it really is. Then a spider dashes crazily across the field of view: It appears enormous, threatening, bristly, unpredictable, and very, very close. This is when the yelping happens. But of course the beast is actually smaller than a pencil eraser and nowhere near my face, so I feel silly, compose myself, and get back to the scale insects.

But sometimes, the startling thing is something I’ve never seen before, something wild and creepy and totally distracting. This is what happened earlier this year when I settled in to identify some newly collected bees from my yard. These were dead bees, mind you, fresh out of a cyanide jar and expected to sit still and not be startling.

The first few toed the line. There was a shiny, bulbous, blue-green mason bee, and a plain little matte-black sweat bee. A ground-nesting Andrena still had flakes of clay on her jaws. All normal and non-threatening.

Andrena bee with strepsipterans peeking out of its abdomen. Photo: Matt Bertone

Andrena bee with strepsipterans peeking out of its abdomen. Photo: Matt Bertone

Then, the yelp. Spreading across the rear end of the next bee was a mass of very alive, squirmy, maggoty little larvae, looking not-so-very little. I knew in split second what they were, but I admit to quickly popping the bee back in the cyanide jar to finish things off before looking again.

I was witnessing the birth of a brood of strepsipterans—a group of parasites whose wacky life cycle involves a weird, blobby insect eating a live bee from the inside out, while that insect’s own babies eat her from the inside. At the time I caught my bee, the strepsipterans had just finished feeding on their mother and emerged into the world, via a hole in their mama’s head (technically, in her cephalothorax). How else?

Had the bee avoided my net and continued to fly around visiting plants, the larvae would have hopped off on the next flower. (Really, hopped: Despite the initial maggoty impression, these are leggy, nimble little insect tykes.) Each one would have waited at the flower-airport to board a fresh bee, which would carry it back to an underground nest tunnel. There, the strepsipteran would find the bee’s egg or larva and burrow in—disappearing inside within a few hours.

The strepsipteran then loses its legs and eyes and grows along with its young bee host. Eventually it fills the bee’s abdomen, stunting its organs and altering its development. Female Andrena bees, for example, develop the angular cheeks and hairy abdomens typical of males. (They also become very hard to identify.) One researcher even reported finding a bee with a single, giant eye arching over its head like a headband–perhaps a strepsipteran-induced developmental glitch.

Strepsipterans emerging from Andrena bee abdomen. Photo: Andrew Ernst

Strepsipterans emerging from Andrena bee abdomen. Photo: Matt Bertone

As adults, male strepsipterans have wings and return the outside world to fly around for a few hours before they die. Females, however, remain ensconced in their bees, with only their heads visible from the outside. (That’s the smooth, yellowish tissue you can see sticking out of the bee’s abdomen in the photos.)

The rest of her body is “a great sack full of eggs,” wrote entomologist W. Dwight Pierce in 1909. The thousands of eggs simply float around inside the mother’s body, absorbing nutrients from her blood. Eventually, they hatch and trek to the outside world via the “brood canal” that exits their mother’s head. Which is where they were when they made me shriek.

This whole stranger-than-fiction setup is more than just a titillating insect freak-show. As parasites, strepsipterans may have an important role in maintaining insect diversity. Parasites tend to regulate their hosts’ populations in ways that prevent any one species from becoming outrageously common—leaving room for more species overall. That process keeps ecosystems diverse and food webs stable.

Stepsipteran larvae emerging. Photo: Andrew Ernst

Stepsipteran larvae emerging. Photo: Andrew Ernst

I would bet that strepsipterans are among the parasites that help maintain diversity, although their role has never been measured. There are about 600 species of strepsipterans in the world, and they can also be found in planthoppers, cockroaches, grasshoppers and wasps. In the bee and wasp species that have been checked, 10 to 30% of individuals carry strepsipterans and are unlikely to reproduce.

That means strepsipterans are common enough to regulate the abundance of their hosts. In a tantalizing example, the European paper wasp (Polistes dominula) left its strepsipterans behind when it moved across the Atlantic to North America—and none of the North American species will parasitize it. So researchers have suggested this wasp’s fast reproduction and dominance over native North American wasps may be due, in part, to the loss of its parasites.

Of course I have no way of knowing where my one bee with her alarming brood of squirmy strepsipterans fits into the big picture. But I’d like to think she’s a good sign. I’d like to think that if I kept looking I would find that my messy yard is teeming with a diversity of slightly creepy parasites, keeping their hosts in line and yielding an endless supply of microscopic scary movies.

November 25th, 2014|Categories: Feature, Natural Enemies, Natural History and Scientific Adventures, Pollinators|Tags: |