Silken choreographies

Biologist Janice Edgerly-Rooks and the extraordinary embiids.

Silken choreographies
Lab work: Janice Edgerly-Rooks, center, assisted in embiid research by students Whitney Knott ’08 and Kathleen Powers ’08 / Photo by Charles Barry

Back when Janice Edgerly-Rooks was a little girl growing up in Meriden, Conn., in the 1960s, a neighbor saw her pushing a baby carriage along the sidewalk. Charmed by this early display of maternal behavior, the neighbor looked inside and saw not a baby brother, a doll, or even a kitten but a squirming nest of hairy tent caterpillars.

Considering that Edgerly-Rooks—now a professor of biology at SCU—would write her master’s thesis on tent caterpillars a decade or so later, the story might suggest an early preoccupation with creepy-crawlies. But she doesn’t think so.

“When I was a kid, we picked up anything,” she recalls. “Turtles were the big thing, or frogs. I wasn’t specializing in caterpillars. There were a lot of creeks and farms nearby, before they built houses everywhere, so we played outside all the time. We used to go into the barns and let the calves suck on our fingers. I don’t know what they thought we were doing.”

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Edgerly-Rooks doesn’t seem to fit any stereotype of solemn scientific preoccupation, although she is a leading world authority on an entire insect order, the Embiidina. She talks about her distinguished career as though slightly surprised by it:

“In high school, I was the kind of student who did okay in everything, although I ended up taking science, which isn’t normal.”

It was in college at the State University of New York, Cortland, that Edgerly-Rooks found herself beginning the journey on the silk road. Her guide was entomologist Terry Fitzgerald, who taught a course on animal behavior. The evolutionary aspect of the subject fascinated Edgerly-Rooks, as did Fitzgerald’s work with undergraduates on tent caterpillars. “I realized: ‘Insects are great!’” Edgerly-Rooks says. “You need somebody to show you, you need to look through the microscope. Most things look worse through a microscope, but insects look better!”

Yet there is one sense in which the baby carriage story seems prophetic. It might be sexist to say that Edgerly-Rooks has an almost maternal solicitude for the insects she studies, but a consistent thread running through her conversation is that—along with finding them intellectually fascinating—she feels protective toward them. After telling the story about the baby carriage— a story, incidentally, that her mother recounted to her later, since she was too young to remember it herself—she hastens to add that the tent caterpillars in her baby carriage weren’t the invasive gypsy moth caterpillars that cause so much damage to forest trees but the more specialized, native eastern tent caterpillar. They were good tent caterpillars.

In the late 1970s and early 1980s, Edgerly-Rooks happily studied the ways that eastern tent caterpillars work together to build their arboreal colonies. But, as so often happens, practicality intruded on youthful infatuation: “When I entered the doctoral program at Cornell, my major professor said: ‘You know, you can’t just keep following Terry Fitzgerald and studying tent caterpillars all your life. You need to find your own subject. Why not work on embiids? Nobody else does.’”

Like tent caterpillars, embiids (pronounced EM-bee-ids) are insects that live colonially in webs they spin out of the strong, sticky proteins that we call silk, but the similarity ends there. Tent caterpillars are the larvae of moths, among the world’s best-known insects. Embiids, also called webspinners, may not be the world’s least-known insects, but they are serious contenders for the title. Their closest relatives, according to Edgerly-Rooks, are the stick insects that weirdly mimic branches or leaves. But embiids don’t look or behave quite like anything else.

Edgerly-Rooks gets protective again when she tries to describe embiids: “Their bodies are very elongated because they spend most of their lives in their colonies. Earwigs are about the only common insects I can think of to compare them to, but that’s terrible because people hate earwigs, and embiids don’t act like earwigs, infesting houses and pinching. Embiids are about as inoffensive as insects get.”

Sweet comments: African embiids built silk tunnels up to reach a slice of persimmon and a raisin. / Photo: Janice Edgerly-Rooks

Until scientists got interested in them, embiids were virtually unnoticed by humans. They don’t eat anything we want or otherwise interfere with us. Various species feed directly on lichens, leaf litter, soil detritus, and other humble plant materials. Humans haven’t found much use for embiids, either. Their silk isn’t woven into fabric as with silkworm moth cocoons or some tropical spiderwebs. Even where people eat insects, embiids aren’t on the menu. When Edgerly-Rooks was collecting in Thailand, two local children who tagged along ate some spider eggs that a fellow researcher found, but not her embiids. The only use Edgerly Rooks knows about is in Central America, where people make bandages from embiid webs (antibiotic chemicals in the silk may help to prevent infections).

Of course, embiids’ economic unimportance to humans doesn’t mean they are unimportant in nature. “The first thing people usually ask me about embiids is what they are good for,” she says. “I could ask what humans are good for compared to embiids, which play a big ecological role in converting plant detritus into soil. If they all disappeared, we don’t know what would happen.”

Embiids are inconspicuous. When Edgerly-Rooks shows me colonies she keeps in her laboratory, the clear plastic containers just seem full of dead leaves until she points out networks of tubular webs on their sides. When she opens a canister, it looks lifeless inside until she begins lifting leaves and revealing slender brown shapes with oddly enlarged front legs that swiftly scurry out of sight. Their cryptic grace makes them seem elfin, like something in A Midsummer Night’s Dream or like small versions of the insect fairy in the recent Spanish fantasy film Pan’s Labyrinth. “Embiid” derives from the Greek for “lively.”

She has pinned a sliver of persimmon to the leaves as a treat, although the embiids can live on just leaf litter. When I ask how many are in the canister, she shakes her head: “I don’t know. Hundreds.” The lab’s dozens of canisters must contain many thousands of embiids, all munching happily on dead leaves and a little persimmon and lettuce. Some colonies have thrived for years since she collected them in the wild.

She has about 30 species from many bioregions, and they demonstrate what is perhaps most unusual about the order. Her species look pretty much alike, and in fact all the world’s embiid species look pretty much alike: “You can look at females of five different species together and not see any differences except maybe in the color. There may be subtle variations, and the eggs can be shaped differently, but on the whole there’s an amazing uniformity of appearance. They’re the only insect order like that.”

On the other hand, Edgerly-Rooks thinks embiid behavior may be unusually diverse and complex. “When I sent embiid behavioral data to a software specialist, he told me it was the ‘longest repeating pattern’ he’d ever seen. They’re not machines. If something happens to their web, they go with their antennae and evaluate the situation and find out what needs to be done and start doing it.”

Embiids are also unusual in that they spin their silk from multiple glands in their enlarged front feet instead of from their mouths like caterpillars. The recent David Attenborough documentary, Life in the Undergrowth, shows an embiid on a rainforest tree on the Caribbean island of Trinidad spinning silk to repair a hole in her colony. Again, there is something elfin about this—like Jack Frost painting a windowpane. “You can’t really see it on the screen, but she was literally bending over backwards to spin,” recalls Edgerly-Rooks, who helped to film the sequence. “Embiids appear to do yoga.” Flexibility in insects in and of itself isn’t unique; think caterpillars. But embiids retain that flexibility as adults. “Most adult insects are built like tanks and have limited to no flexibility,” Edgerly-Rooks says. “It’s kind of like wearing a coat of armor. It would be hard to do yoga with that kind of body.”

Edgerly-Rooks found working on the documentary “a blast,” although it challenged her protective feelings: “I was the insect wrangler, and the director had this huge storyline of things she wanted them to do. The director and cinematographer wanted to show embiids drinking, so before that we couldn’t give them water for days. They wanted to show predation, so we had to sacrifice embiid females to this gecko. I was almost in tears: ‘Don’t make me do that again!’” She also thinks the episode she worked on—about silk-spinning invertebrates in general—spends too much time on spiders and not enough on embiids. The gecko-feeding sequence was cut, although the finished documentary has a shot of water rapidly draining from an embiid web as a thirsty occupant drinks it from inside.

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All embiids—male and female, adult and immature—spin the silken tubes wherein they spend most of their lives, but spinning behavior varies. Some species spin more silk than others, and different species have different spinning patterns. Edgerly-Rooks calls the patterns “choreographies,” and the intricate, rhythmic ways that the little insects wave their legs to produce and distribute the silk does seem like dancing. Embiids that live in soil or leaf litter tend to spin just enough silk to make their tubes and form small colonies. Species that live aboveground on tree trunks or rocks may spin protective sheet webs over their tubes, and the sheets can shield large colonies.

Embiid silk varies in color from brilliant white to blue or pink, and large aboveground colonies can be easily visible to people who know about embiids. In Thailand, Edgerly-Rooks found pink colonies on trees at guesthouses where she stayed. But people who don’t know about embiids tend not to notice even large colonies, or they assume that spiders spin them.

As with most insects, embiid females are the main players in the life cycle. Wingless and sedentary, they make the colonies. Female care of eggs and young, generally uncommon among insects, is a basic trait of the Embiidina. Unlike termites or ants, however, embiid colonies don’t have hierarchies and division of labor. They are groups of females that live together because it helps them to guard their eggs and babies (called “nymphs” since they hatch resembling small adults instead of as worm-like larvae). On reaching maturity, young individuals usually leave their natal colony and join another or establish one of their own.

In 1986, Edgerly-Rooks wrote her Cornell Ph.D. dissertation on female natal care that she observed at the Asa Wright Nature Center Field Station on Trinidad. “Because the British had owned the island, there was a big natural history literature, so it seemed like a good place to study them. When I got to the field station I found colonies all over the trees. But nobody knew much about them, so I’d take an umbrella into the rain forest and watch embiids all day. And I soon found out one reason why the females guard their eggs in colonies.

“There are little wasps that parasitize embiid eggs by laying their own eggs inside them. Whenever I was at an embiid colony, the wasps were waiting around within the silk. And whenever the web got torn for any reason, the wasps mobilized to attack the embiid eggs, because the mother embiid was distracted by her repair work. So if the female embiids weren’t guarding their eggs all the time, they lost them. And it took six weeks for the eggs to hatch; that whole time the maternal females have little time to feed themselves, because they’re on guard duty. So I could see one ‘why’ of embiid social behavior. As soft-bodied, sedentary animals, embiids are very vulnerable to predators.” Edgerly- Rooks pauses, then explains, “Actually, the adults aren’t all that vulnerable, because they can run really fast, and they can run backward even faster than forward. They can do incredibly fast inside-out u-turns. But the eggs and nymphs are easy targets. So there’s a selective advantage for females to join with each other, because something like a wasp is less likely to get into a colony if many females are maintaining it than if just a few are.”

There are trade-offs to forming large colonies, though. “The bigger the embiid colonies get, and the longer they last, the more wasps and other predators they attract.”


Fancy footwork: She uses her fuzzy mitts to weave a covering of waterproof silk. Native to the Mediterranean, this species of embiid is now found in California as well.

Embiid males resemble male ants, in that they exist mainly to mate. They search for colonies of females with chemoreceptors on their elongated antennae, and when they find one they try to get inside the silk tubes, often facing resistance from the residents as well as competition from other males. A male that finds a willing female performs a courtship ritual that involves twining his body around her.

Embiid males are winged in some species, wingless in others. Winged males don’t feed after maturity so their lives are brief. Wingless males continue to feed, and may move into colonies to keep other males away. In some species, such males have enlarged heads and jaws, which may help them to guard the females. Some other males of such species are slimmer and may be “mimicking” females as a way to get around the big-headed males in competition for mates. But Edgerly-Rooks says this hasn’t been adequately studied yet.

Some embiid species have dispensed with males and are parthenogenetic—a Greek and Latin cognate word meaning “virgin birth.” The females produce nymphs—always female—without mating. Embiid males are indispensable to science, however, because the shapes of their genitalia are among the few features by which taxonomists can distinguish at least the sexual species. “Another reason that embiids are obscure,” Edgerly-Rooks wryly complains, “is that most field guides just illustrate them with a squashed male on a slide.”

Edgerly-Rooks has found a lot of embiid species in the three decades she’s been studying them. Although they aren’t very diverse by insect standards, there may be as many as 2,000 species in 14 families. Six of the families are new. One of the main problems she’s encountered in her research has been that embiids she wanted to study weren’t classified. It’s hard to write a scientific paper about an unnamed species.

“I’d take specimens to Ed Ross, a 93-year-old taxonomist at the California Academy of Sciences who has named most of the embiid species known today. And he’d say: ‘Oh, that’s a can of worms. I haven’t gotten to that yet.’ So I wound up describing and naming species myself. I just named one for my husband, Edward. Edward has helped me a lot studying embiids in the field, even more than he’s wanted sometimes.”

Edward Rooks is a wildlife artist and photographer who also teaches parttime at SCU. He has made striking paintings of tent caterpillars and of birds attacking an embiid colony as well as more conventional subjects like penguins and eagles.

Studying embiids in the field has led Edgerly-Rooks to some out-of-the-way places. Yet another reason for embiids’ obscurity is that they tend not to live near scientists. Embiids are an ancient order, occurring on every continent except Antarctica, but they seem never to have adapted to cool climates, and most species live in the tropics. The few species native to the United States occur in the South or along the Mexican border.

“Some of the places embiids live are quite beastly,” Edgerly-Rooks says. “We did a study on an island off Queensland, Australia, where two species are common. I wanted to compare the different ways they’ve adapted. One species lives on lichens in rocky, often very hot places, like granite cliffs; one lives on soil detritus in grassland or eucalyptus woodland. And they are adapted in all kinds of interesting behavioral and physiological ways. But it was a nasty place for us to adapt to. You knew just from the names of the plants—spear grass, sword grass, porcupine grass—and there was a very abundant weaver ant with a very bad attitude. My poor husband in the lead was constantly under attack. Sometimes it was a question of walking past an ant colony or walking off a cliff.” Some embiid colony sites were in gullies with limited sun; inspired by the lichens Edgerly-Rooks and her husband found there, they gave the sites names like “drab” and “ugly brown.” At the same time, Edgerly-Rooks says, “The beauty of the island and its wildlife kept us happy and sane. We often found ourselves saying, ‘Good thing this place is beautiful, because it sure hurts to work here.’”

Civilization is changing embiid distribution, though, as some species hitch rides on ships and other transport. Although the Bay Area has no native embiids, two genera have colonized within the past century or so. The nimble, cryptic insects take advantage of suburban growth: “They spin their webs in mulch or other stuff used in landscaping, so the more people move the stuff around, the more embiids they get. I just found webs in the mulch around a new parking lot outside the lab here on campus.”

One genus, Haploembia, is from the Mediterranean and is now common in the Bay Area, spinning bluish webs under rocks. Entomologists once thought it was a single parthenogenetic species, but then males turned up in Redwood City and Mountain View. It was an SCU student, Natasha Calvert ’05, M.A. ’07, who found the Mountain View males.

Edgerly-Rooks thinks that there may be two Haploembia species here—one with males and one without. The other genus, Oligotoma, comes from the Middle East and is less common here than Haploembia, suggesting that it arrived later. But it reproduces faster, so it will probably increase. It has colonized many countries—sometimes to Edgerly-Rooks’ chagrin, when she travels in search of new embiids and finds that Oligotoma has gotten there first.

Edgerly-Rooks hasn’t devoted her entire career to silk-spinning insects. Beginning with postdoctoral work at Clark University, she conducted a study funded by a grant from the National Institute of Health on the ecology and behavior of treehole mosquitoes. The mosquitoes, which breed in water that accumulates in forest tree hollows, can carry epidemic diseases like yellow fever. That deadly disease mainly occurs in the tropics now, but historical outbreaks have occurred in the United States, and mosquito species that have invaded recently might serve as new vectors. Edgerly-Rooks studied factors that inhibit hatching of the mosquitoes’ eggs: “One factor that can inhibit egg hatch is competition among the larvae,” she concluded. “If a female lays eggs when a treehole is too crowded, they may not hatch. So we set up these huge experiments in the field to isolate exactly what the inhibiting factor is.”

Edgerly Rooks came to Santa Clara’s biology department in 1988. “Some people only apply to large universities where they can mainly do research,” she says, “but I applied to smaller places where I could balance research and teaching. Because there’s no graduate biology here, I started by teaching ecology and animal behavior. I didn’t get around to teaching entomology until 1997, several years after I got tenure.”

Embiids have remained her fascination, going back to her original motive for studying animal behavior—the “why” of things. She recently embarked on a “life-changing” study of the relationship between embiid behavior and evolution, funded by the National Science Foundation. Collaborating with a taxonomist and a molecular biologist, she has been observing embiids from all over the world.

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Micromanagement: Kathleen Powers ’08 sets a micrometer to measure the size of an embiid’s hairy, silk-spinning feet. / Photo: Charles Barry

“The evolution of a group of organisms has usually been studied through its morphology, through its physical organization,” she says. “But since embiids all look so similar, yet have such complex behavior, it raises the question as to whether we can look at an organism’s evolution through its behavior as well as its morphology. For example, how have all the different web-spinning choreographies that embiids perform evolved? Can we categorize groups of embiids by their spinning choreographies, and perhaps see how spinning behavior might have affected evolution from one group to another—what we call phylogeny? And then, how has spinning affected the evolution of their social behavior? Embiids are a ‘primitively social’ order, so they may show us a lot about how organisms evolve social behavior in the first place.”

Edgerly-Rooks’ entomology students are participating in the study. “I find working with undergraduates very rewarding,” she says. “This year I’ve been on sabbatical, so I’ve spent most of my time with five students. They work really hard and they don’t mind doing things that are kind of repetitive, like recording all the different motions an embiid makes during its silk-spinning choreography.” She notes with some satisfaction that some of the students have won awards for their embiid projects.

Although Edgerly-Rooks isn’t solemn about her research, she is formidably enthusiastic about it. As she scurries around her lab—from the embiid colonies to a computer, to another computer, and back to the colonies—demonstrating the vast array of films, charts, statistics, and other data that she and her co-workers have amassed, she begins to seem a little embiid-like herself, using a technological choreography to spin a complex web of ideas and information. The concept of a human with embiid qualities isn’t new to her:

“Spider-Man is really Embiid-Man, you know,” she says. “He spins his silk from his front appendages like an embiid.” She waves her hands to demonstrate the embiid technique. “If he spun it from the tip of his abdomen like a spider, it would look pretty weird in the movies.”

David Rains Wallace is the author of 16 books on natural history, conservation, and related subjects—most recently Neptune’s Ark: From Ichthyosaurs to Orcas, published by the University of California Press.

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