Shocking news? Perhaps… When capturing insects in their webs, spiders get a little help from electricity, according to a new study by UC Berkeley scientists.

Postdoc Victor Manuel Ortega-Jimenez, working in Berkeley’s Animal Flight Laboratory, usually studies hummingbird flight, but became interested in how spider webs attract insects while playing with his four year-old daughter. “I was playing with my daughter’s magic wand, a toy that produces an electrostatic charge, and I noticed that the positive charge attracted spider webs,” he says. “I then realized that if an insect is positively charged too, it could perhaps attract an oppositely charged spider web to affect the capture success of the spider web.”

As mentioned in our “Bee Positive” video, as insects fly through the air, they naturally become positively charged. Spider webs, on the other hand, are normally negatively or neutrally charged.

To test his spider web hypothesis, Ortega-Jimenez found cross-spider (Araneus diadematus) webs along streams in Berkeley and brought them into the lab. He then used an electrostatic generator to charge up dead insects—aphids, fruit flies, green-bottle flies and honeybees—and drop them into a neutral, grounded web.

“Using a high-speed camera, you can clearly see the spider web is deforming and touching the insect before it reaches the web,” he says. Insects without a charge did not do this. (Video is available here.)

Ortega-Jimenez also suspects that light, flexible spider silk, the kind used for making the spirals built on top of the stiffer silk that forms the spokes of a web, may have developed because it more easily deforms in the wind and the presence of electrostatic charges to aid prey capture.

“Electrostatic charges are everywhere, and we propose that this may have driven the evolution of specialized webs,” he says.

The findings were published last week in Scientific Reports.

Photo by Victor Manuel Ortega-Jimenez, UC Berkeley

Even though most of them are harmless, spiders tend to have a bad reputation. But now, two publications find that maybe this bad rap is warranted.

The first, published this month in Behavioral Ecology and Sociobiology, looks at Micaria sociabilis, a small ground spider. Like several other spider species, M. sociabilis demonstrates sexual cannibalism, where one gender eats the other before, during, or after mating. Unlike most other sexual cannibals, however, for M. sociabilis, it’s the males that do the dining.

As National Geographic News Watch explains, it’s not hard to understand female cannibals in nature:

Females invest much more energy into egg production than males do in sperm production, which tends to make them pickier about who they mate with.

But why male cannibals? Czech scientists Lenka Sentenská and Stano Pekár decided to find out by watching M. sociabilis for about two years in the lab. Throughout the research, the spiders were well-fed to discount cannibalism due to hunger.

Over the course of 160 male-female spider encounters, the researchers noticed that when the males ate the females—and about one third of them did chow down—it was often prior to any mating. They also noted that when dining on a member of the opposite sex, the male spiders didn’t seem to discriminate between the size of the female or whether the female had previously mated. But when looking at the age of a female, the scientists found that the male spiders preferred to eat older females. And in fact, the males ate the older females about 60% of the time they were introduced. A brief video of the cannibalism is featured here. (Yum!)

“Our study provides an insight into an unusual mating system, which differs significantly from the general model. Even males may choose their potential partners and apparently, in some cases, they can present their choice as extremely as females do by cannibalizing unpreferred mates,” Sentenská and Pekár explain.

Another study, published last week in Ecology Letters, finds that for the species Anelosimus studiosus, it pays to be cruel.

Spiders in this species come in two distinct varieties—aggressive and docile. Aggression is passed down through the parents. Researcher Jonathan Pruitt wondered which temperament might be more successful in nature. So he paired them up in the lab—creating some aggressive-aggressive pairs, some docile-docile pairs, and some mixed. He then took the pairs, 90 in all, back into the woods where they were originally collected and watched them reproduce and colonize over the next five years.

For half of the pairs, Pruitt meticulously kept predators away. He left the rest to fend for themselves. For the tended spiders, the population sizes were similar after five years. But for the others, it was quite a different story.

After two years, the docile spiders were booming—they spent all of their time reproducing and didn’t worry about invaders. But, after three years, the docile spider population was decreasing due to predation and to other insects and spiders stealing their prey. And by five years, the docile spiders were all but gone. Only a quarter of those from the mixed pairs remained.

On the other hand, three-quarters of the aggressive-aggressive colonies remained. Survival of the meanest, perhaps? At least when invaders threaten, says Pruitt in ScienceNOW. “Species without defense might be driven to extinction by enemies.”

Image: Lenka Sentenská

When you and I look at spiders, we might see something creepy or cool (depending on your inclination), but when these scientists look at spiders, they see millions of years in the past.

Charles Griswold, Hannah Wood, Rosemary Gillespie and Nick Matzke painstakingly studied a superfamily of spiders called Palpimanoidea, aka assassin spiders.

The Academy and University of California researchers wanted to determine how these spiders are related and distributed and how that’s changed for the millions of years they have lived on Earth.

This superfamily has been assembled and separated many times over the past three decades.  The superfamily includes the trap jaw spiders (Mecysmaucheniidae), forest rubies (Stenochilidae), the mysterious Hutton’s spider (Huttoniidae), palp-footed spiders (Palpimanidae) and the pelican spiders (Archaeidae).

They’re called assassin spiders because all of the families except the trap jaw spiders hunt, kill and eat other spiders. Trap jaw spiders have an unusual feeding pattern, too. They have incredibly strong and fast jaws that lock open and then release quickly to trap prey.

While most of the living species within the assassin spiders live in the southern hemisphere, grouping these spiders is tricky because they have disjunct distributions, separated by barriers, namely large oceans.

Scientists love when things are tricky: it raises new questions to research. That couldn’t be more true for this group of folks. Charles has always been interested in biogeography and continental drift. Rosie Gillespie has always been interested in life on islands—what lives there, how did it get there and how did it diversify? Hannah’s fascinated by the pelican spiders and Nick is a paleontologist and computational biologist, attracted by the statistics of dating phylogenies.

It’s good that their interests are diverse, Charles says. “Science has become technologically and mathematically complex. It now requires a team of researchers.”

Hannah and Charles traveled throughout the southern hemisphere collecting and studying these spiders for many years. To answer the tricky questions this superfamily poses, they began with a thorough comparative morphology of all the spiders, living and extinct. Many of the fossils were specimens trapped in amber—which preserves the spiders “like new,” Charles says.

The scientists used whatever tools they could get their hands on—microscopy, current dissection technology, CT-scans, even the synchrotron at the Advanced Light Source at UC Berkeley.

The team gleaned data from DNA collected for every living spider. Then came the number crunching. Data were processed on the computer cluster here at the Academy and the San Diego Super Computer Center.

Charles explains that their findings confirm four different theories.

First, they confirm that these spiders all belong to Palpimanoidea.  “The phylogeny and classification encompasses the true scope of the superfamily,” Charles says.

Second, one of the fossil spiders they studied, an Archaeidae species, was discovered in the northern hemisphere. But all of the living relatives reside in the southern hemisphere. As David Byrne might ask, “How did I get here?” Charles and Hannah have an answer—continental drift. The lineage is so ancient, it’s consistent with the dates of continental drift.

Third and fourth, these spiders are found on the islands of Madagascar and New Zealand.  Geologists know that these two islands were originally pieces of their nearby continents that became separated. When they broke-off is clear, Charles says, but what is controversial is if some life forms have been around since the islands were connected to continent. .  Many animals and plants may have dispersed there.  The dates of these spiders originate prior to island separation, showing they have endured since the islands first broke away from the continents.

This superfamily of spiders, Charles says, is one of the “best examples of distribution that reflects continental drift. The distribution patterns, age of the fossils, and dates of phylogenic diversification are old enough. It’s one of the best documented cases of the results of continental drift.”

If you’ve seen our Earthquake exhibit, you know there are other examples of animal and plant evidence of continental drift. These spiders add nicely to it.

The study was published last month in Systematic Biology.

Charles will now take these methods to look at the biogeography of other groups of spiders. Hannah is looking more deeply into the trap jaw mechanism of those amazing spiders. Stay tuned for more spiderific stories!

Huttonia spider image: SE Thorpe/Wikipedia

The tree resin that forms amber acts like an amazing time machine. It freezes items—plants, insects and other life forms—in near perfection, later turning into a semi-precious stone for scientists to study millions of years later.

The latest amber find, from Myanmar, is the only fossil ever discovered of a spider attacking prey caught in its web. The research is published this week in Historical Biology.

“This juvenile spider was going to make a meal out of a tiny parasitic wasp, but never quite got to it,” says lead author George Poinar, Jr. of Oregon State University. “This was the wasp’s worst nightmare, and it never ended. The wasp was watching the spider just as it was about to be attacked, when tree resin flowed over and captured both of them.”

Both the spider and wasp species are currently extinct, but provide clues to earlier life. This type of wasp, Poinar says, belongs to a group that is known today to parasitize spiders and insect eggs. In that context, the attack by the spider, an orb-weaver, might be considered payback.

Somewhat surprisingly, the piece of amber also contains the body of a male spider in the same web. This provides the oldest evidence of social behavior in spiders, which still exists in some species but rarely. Most spiders have solitary, often cannibalistic lives, and males will not hesitate to attack immature species in the same web.

Perhaps Howitt said it best in her poem (changed a bit here):

And take a lesson from this tale, of the Spider and the Wasp!

Image: Oregon State University

They found an unusual spider while combing the caves and sent it to a student researcher here at the Academy to identify. She had trouble putting the specimen to a species and sent it on to a postdoc down the hall. He had the same trouble.

Enter Charles Griswold, head of arachnology at the Academy. Charles identified the mystery spider as the feared brown recluse at first, but then he looked closer. “The eyes were all wrong, the claws wrong, the jaws wrong. It was not a brown recluse,” he says.

Now Charles knows a lot about spiders, but even he knows when he’s stumped. So he consulted the bible for spiders in the US—Spiders of North America. The spider, nicknamed Mysteridae, wasn’t in it. He consulted the world guide. Not there, either. “It didn’t fit anything, “ he says.

Charles, postdoc Joel Ledford, and student Tracy Audisio dissected the specimen and examined the spider’s anatomy. The more they investigated, the more they realized that this spider didn’t match up with any family they’d seen. They reached out to colleagues and one recognized shading at the spinnerets, or spinning organs, similar to shading on goblin spiders. Still, the breathing organs (tracheae) and enormous claws were nothing like goblin spiders.

So Charles, Joel and Tracy realized they had a whole new spider, from a whole new family, related to the goblin spiders. And they named the new spider Trogloraptor marchingtoni—troglo meaning caves and raptor, meaning grabber, seizer, or robber.

And marchingtoni? For Neil Marchington, deputy sheriff, amateur biologist and cave conservancy member who found the spider in the first place!

The species is described in ZooKeys.

Images: Trogloraptor; Joel Ledford, Charles Griswold, Tracy Audisio

Or so goes a new study in published in Biology Letters last week. According to that abstract:

We conclude that the mechanism [genital break-off] may have evolved in response to sexual cannibalism and female-controlled short copulation duration.

Dang! You have to respect evolution!

And that’s the theme of a new exhibit opening at the Academy later this week: Animal Attraction—“sex drives evolution; nothing in life is more important.” The exhibit includes animals, specimens, images, videos and the weird and wild stories behind animal reproduction. In one species, the coral banded shrimp, the deviant mating behavior is monogamy. Well, sociopathic monogamy. We’ve produced a Science in Action video to supplement the exhibit explaining the mating habits of nearby elephant seals and banana slugs—very different mating strategies, but equally dangerous.

Which brings us back to these Nephilengys malabarensis spiders. As Ed Yong reports in Nature News:

Male spiders deliver their sperm through a pair of structures known as palps, which are found on the sides of their heads. By observing sexual encounters between 25 pairs of virgin N. malabarensis, [lead author Daiqin] Li’s group found that every coupling ended with damage to the male’s palp. In 12% of cases it was partially severed; in the rest it snapped off completely.

Yikes! But not only does the palp continue to deliver sperm to the female spider, it also blocks the entrance should she encounter another male spider. And, as we reported a couple of weeks ago, even as a eunuch, the male spider is still tough, actually becoming better fighters “without their heavy palps,” says Yong.

Passing along their genes long after mating, becoming better fighters and, perhaps most importantly, staying alive—these spiders are highly evolved to survive. Well done!

Image: Joelyn Oh

Happy Halloween! We thought we’d get you in the mood with spiders and some of the creepiest ones, to boot—Lycosoidea.

What are Lycosoidea? They are the wolf spiders and their kin, with probably 10,000 species around the world, known and undiscovered (what’s that under your bed?). Since they are major predators (and prey) around streams and rivers, they are ecologically vital. The legendary tarantula of the Mediterranean, a supposedly venomous spider for which the only bite cure is to dance the tarantella, belongs here. Schizocosa is a model organism for studies in invertebrate behavior, perception and learning, and Cupeinnius is the model for understanding spider senses (just ask Tobey Maguire). The South America tropical wolf spider Phoneutria, with its deadly combination of venom, attitude and familiarity, is probably the most dangerous spider in the world.

The California Academy of Sciences has one of the world’s best collections of these spiders. During September, spider experts and students from across the US and from three countries in South America met to study the collection and share information. The aim was to understand the phylogeny—or evolutionary history—of Lycosoidea. From this understanding, the scientists hope to make generalizations about invertebrate evolution and geography and make predictions about venoms and venom therapies.

Collectively these researchers are assembling a dataset of more than 300 observations across 80 species, representing the full range of these spiders.

Participants included the Academy’s Charles Griswold and Darrell Ubick, Tracy Audisio and Liz Morrill (San Francisco State University), Natalia Chousou Polydouri (UC Berkeley), Petra Sierwald (Field Museum in Chicago), Diana Silva Dávila (Peru), Luis Piacentini (Argentina), and Lina Almeida, Daniele Polotow and Estevam Cruz (Brazil).

The “Lycosoidea Summit” was made possible by the resources of the Academy, including gifts from the Schlinger Foundation and estate of Bill and Maria Peck, the Lakeside Fund for International Students, and the Harriet Exline Frizzell Fund of the Academy’s Department of Entomology.

I asked Charles, our fearless curator of arachnology, why he studies these spiders.

Nothing really makes sense except in the context of evolution, and our job is to map evolution. So the evolution of a big, ecologically and medically important group like these spiders is information that some of us need now, and everyone may need in the future.

Our aim is to find the phylogeny, or evolutionary tree, of these spiders. So we’re not specifically studying venom, or behavior, etc., except insofar as these data help to inform the phylogeny.

But, in the case of deadly spiders like Phoneutria, an understanding of its place in the phylogeny also provides a potential map of the evolution of its venom.

Learn more about the research Charles and his colleagues do here. He was also featured recently on ABC7’s production of “Reefs to Rainforests: The Great Expedition,” available online here.

Greg Farrington is the Executive Director of the California Academy of Sciences.

Image: Opoterser/Wikipedia

For the male golden orb weaver spider (Nephila pilipes), chivalry is a gentle back rub, calming the female during multiple copulation sessions. Researchers actually call this “mate binding”—in which the male spins a fine silk and spreads it about the female’s backside.

Researchers from Singapore and the US wanted to know if it was the scent of the silk that calmed the females, or the “tactile communication” of the back rub. Using super glue and other tools in their kit, the scientists ran a series of tests on the spiders. The result? National Geographic News reports:

All 17 females that couldn’t “smell” calmed down after getting a massage. Females that couldn’t “feel” were less likely to let their mates get it on more than once—about 40 percent weren’t calmed…

Of those that weren’t calmed (and couldn’t feel their backrubs), many ate their mates—a common practice in the spider world.

This research, published earlier this month in Animal Behavior, shows that chivalry is a form of stayin’ alive for these spiders.

Male field crickets (Gryllus campestris) also perform chivalrous acts as a form of survival. Not necessarily their own, however.

Scientists often witnessed these crickets in the lab guarding the female after mating. These possessive males know that if another male gets close, his chance of offspring go down—a second mate’s sperm can flush the first delivery. Researchers thought from this behavior that the first male was aggressively coercing the female to stay close.

But scientist Rolando Rodriguez-Munoz wondered how these insects behave in the wild, outside the lab, and set about videotaping them. Instead of aggressive coercion, Rodriguez-Munoz found the male crickets protect the females from predators, occasionally even at the cost of the male’s own cricket life. ScienceNOW explains the findings:

When pairs hang out outside their holes [burrow homes], males tend to sit farther away from the entrance, letting females stay closer in. That makes it easier for the buzzing females to duck away from oncoming predators like magpies; males, however, become an easy lunch.

If they do live, though, the rewards are great—they’ll likely mate again. In effect, the male crickets trade a longer life span for greater success in fathering offspring with their partners. The research was published in Current Biology.

Image: Roberto Zanon