Spider’s Jump Stabilized By Silken Line

Human jumpers are pretty pathetic when compared to jumping spiders. These arachnids can hurdle themselves to destinations of various heights and cover distances up to 25 times their own body length. That’s like a six-foot-tall man jumping 150 feet, starting from a standstill.

Most jumping spiders attach a silk dragline to their starting point, which was thought to be a safety line. That line has a second purpose, researchers have just found — stabilization. They report their findings in the Journal of the Royal Society Interface.

The team of researchers from Taiwan captured 27 Adanson’s house jumpers (Hasarius adansoni) near Taichung City. Twenty-two of the spiders deployed silk when they jumped, and five did not. The five that didn’t use silk ended up being natural controls in a jumping test, letting the researchers compare jumps with and without silk. The scientists had each of the spiders leap three times, filming them with hi-speed cameras (see video above for an example of a jump).

Spiders that used a dragline had a stable body position in the air and a smooth landing. Those that didn’t, however, pitched rearward in the air and landed more upright, falling forward and slipping or tumbling as they made contact with the ground.

“These results suggest that dragline silk can function as a body stabilizer to prepare salticids [jumping spiders] for a predictable, optimal landing posture,” the researchers write, “and hence is critical for these agile and efficient hunters.”

Video from Kai-Chung Chi et al.

More Than Just Seagulls Munch On The Seashore

journal.pone.0068221.g005Walk along pretty much any beach and at the high tide mark will be a line of debris. There may be seaweed or shells, bits of driftwood or plastic debris. You probably won’t see any fish, though. And that’s a little odd, because fish do die, and their bodies have to go somewhere. Surely some would wash ashore.

A group of researchers in Australia think that they’ve figured out where the fish go – the fish quickly get scavenged by the critters that live along the shore. But there’s more than just seagulls finding their meals here, the team reports in PLOS One.

The scientists set up a series of experimental plots along a sandy beach on North Stradbroke Island on the east coast of Australia. They picked a spot far from humans, where dogs and beachgoers would be scarce. Then they set out 20 plots, three meters by 10 meters each, and for eight days added about five kilograms of flathead mullet fish to half the plots about two hours before sunset.

The beach was nearly picked clean. Over the eight days, 720 fish were set out and 97 percent were completely eaten. Gulls (silver gulls in this case) ate some of the mullet, but there were several other birds species as well: Torresian crows, whistling kites (b in image above), brahminy kites (a), and white-bellied sea eagles (c and d)

These avian scavengers scoured the beach most often at sunrise and in the first few hours of morning. On three occasions at night, however, red foxes (f) visited the plots, snapping up the easy meal. And on one day, a lace monitor (e) – a large, carnivorous lizard – was spotted on the beach snacking away. That was a surprise because there have been few reports of terrestrial reptiles scavenging on a beach.

One invertebrate also got in on the action. The researchers measured the diameter of ghost crab burrows and, using burrow size as a proxy for crab size, discovered that when they added fish to the experimental plots, bigger ghost crabs moved in to take advantage of the free food.

But birds were the dominant consumers of the carrion fish. And they probably play an important role in this seashore ecosystem, the researchers say, helping to transfer nutrients from the sea onto land and providing a vital link between water and soil.

Image used under Creative Commons license, Schlacher TA, Strydom S, Connolly RM, Schoeman D (2013) Donor-Control of Scavenging Food Webs at the Land-Ocean Interface. PLoS ONE 8(6): e68221. doi:10.1371/journal.pone.0068221

Caterpillars Can “Blink” A Fake Eye

22373_origMany animals have a fake eye — or eyespot — or two that they can use for protection from predators, often by frightening or distracting the hungry creature. Eyespots are especially common among tropical caterpillars. And researchers conducting a caterpillar inventory in Costa Rica have documented two species (Eumorpha phorbas, above, and E. labruscae) in which the eyespots can sort of blink. They report their findings in the Journal of Natural History.

How can an eye that’s not real blink? To find out, Thomas J. Hossie of Carleton University in Ottawa, Canada, and colleagues collected and reared caterpillars of the two species. When each species reaches the last instar before turning into a moth, it takes a form that has an eyespot on a tentacle that pops up from its butt; this is known as the anal horn. For the study, the researchers would remove a caterpillar from its rearing bag, let it acclimate for a minute, and then prod its rear three times. The result was a “blink,” such as the E. labruscae captured in the video below:

“Both caterpillars can ‘blink’ their posterior eyespot upon perceiving a threat,” Hossie writes on his blog Caterpillar Eyespots. “That is, they can move the skin around the eyespot such it either conceals/reveals the eyespot or flashes (i.e. reflects light) conspicuously towards an onlooker.”

Being able to blink the eye would make it look more like a mammal or bird eye, which is a little odd because scientists had thought that the eyespots on caterpillars were supposed to look more like snake eyes. Snakes can’t blink because they don’t have eyelids. Unfortunately Hossie and the other researchers haven’t been able to test how predators respond to these distinctive eyespots — including whether they might interpret them as mammal, bird, or snake — because these are really rare species.

But Hossie notes on his blog that these caterpillars have another defensive trick that is truly snakelike: “Interestingly,” he writes, “both Eumorpha caterpillars also inflate their thoracic body segments, while pulling their head into their body, to form a diamond shape which appears similar to the head shape of dangerous co-occurring snakes (at least to human observers).”

Image copyright CAPEA, used with permission under Creative Commons license

Bad News For Animals That Live In The Subnivium

voleYou’ve probably never heard of the “subnivium.” That’s because it’s a term that scientists just made up (they do that). The group of ecologists and biologists, led by Jonathan Pauli of the University of Wisconsin, say in an article recently published in Frontiers in Ecology and the Environment that the subnivium is the seasonal refuge that occurs below the snow where there’s environmental stability. It’s cold there, with temperatures near freezing, but this region serves as a retreat from the harsh, sometimes changeable environmental conditions above.

A healthy subnivium contributes to a healthy ecosystem. Insulated soil lets microbes and fungi breathe and proliferate and process organic matter. Plants benefit from increased carbon dioxide and warmer temperatures, especially during late winter and early spring. Many animals — a list that includes invertebrates, amphibians, reptiles, birds, and small mammals — will use the region to hide out during the winter, feeding off each other or any vegetation they can find. There are whole ecosystems below the snow.

But warming conditions have led to many changes in the patterns of snow in the Northern Hemisphere (that’s where most of the world’s snow is found): The month of maximum snow cover has shifted from February to January. The spring melt is about two weeks earlier than it was decades ago. The extent of land covered in snow in the winter has been shrinking. In many places, the amount of time when snow is more likely than rain has decreased by more than one and a half months. Snow depths are decreasing, as are snow packs. The list goes on and on.

“Snow cover is becoming shorter, thinner and less predictable,” Pauli said in a statement. “We’re seeing a trend. The subnivium is in retreat.”

With all these changes, the stability that the subnivium provides is therefore disappearing. What does that mean for the ecosystems that thrive there? One worry is that organisms, such as plants, that are exposed to cycles of freezing and thawing could experience tissue damage. Others, like voles or insects, that lose the layer of snow that hides them may be subject to predation by birds or other critters.

“Decay of the subnivium will affect species differently, but be especially consequential for those that lack the plasticity to cope with the loss of the subnivium or that possess insufficient dispersal power to track the retreating range boundary of the subnivium,” the researchers write. Those that can adapt to the loss of stability or can move to places where there’s still reliable snow cover will do better than others. Adapt or move — those seems to be the only two options for surviving climate change.

Image of vole courtesy of flickr user musubk

Should I Be More Scared Of Spiders?

spideroThis weekend, a friend posted on Facebook that she’d been trapped in her basement after spotting a spider on the wall by the stairs leading back into her house. She wondered what she would have done if her husband hadn’t returned soon after the incident.

“Walked by the spider up the stairs?” I flippantly replied.

Her fear wasn’t unusual. About half of women and 10 percent of men have arachnophobia. There’s some debate about whether the fear is innate or learned, but it’s definitely real. And it can even make spiders look bigger than they actually are. (Which accounts for my friend saying that her spider was “Godzilla-sized,” which was highly unlikely.)

But spiders don’t scare me, at least not spiders in the United States. When I was in Australia, it was a different story. Before my first trip there, I’d read a book about all the ways you could die in that country. It said not to worry about scorpions because their bite would only hurt; spiders, though, could kill. So when I spotted a spider in my friend’s garage, I stayed far enough away that I couldn’t identify it. It seemed safer that way.

Back at home, when I spot an interesting spider, I’ll grab my phone and get as close as I can to take a photo. That’s how I got the picture above — the spider was pretty, a species I’d never seen before, and I wanted to identify it. (I think she’s a venusta orchard spider, but that’s only an inexpert guess.)

That’s not to say there aren’t venomous species in this country. The brown recluse and black widow spiders are deadly. And there are an average of 6.6 spider-related deaths in this country each year. Australia, in contrast, hasn’t had a confirmed spider bite death since 1979.

Does that mean that I should be more scared of spiders here at home, or less afraid in Australia?


Australia Museum says that the development of antivenom accounts for the lack of spider bite deaths there. Plenty of people get bitten, but they get treated quickly enough that they don’t die. It’s likely a similar story in the United States. Most of the deaths here are kids who don’t get treatment fast enough. (That makes sense — children are curious and can get into trouble, and they can have difficulty telling someone what’s wrong.) Perhaps parents in Australia, where there are so many deadly natural threats, are simply more vigilant.

And a little vigilance isn’t a bad thing. A venomous bite isn’t going to be fun, so avoiding potentially deadly spiders is a good strategy. Just keep a wide berth as you pass one if you’re worried that its bite could hurt.

But back to my friend on Facebook: I feel somewhat bad that I was so flippant in my reply, but spiders generally are not something to be frightened of. They’re fascinating creatures that I’m usually happy to have around the house because they eat annoying critters, like mosquitoes. Though, I will admit, if I found one of these bat-eating spiders in my living room, I might be tempted to call in an exterminator.