Deep in the jungle, a headlamp shines on a dissection in progress. “There are eggs,” says , staring at the spider-shaped clump he had pulled from a silky orb web earlier that afternoon. He tugs at the clump, and something inside stirs.

“Oh, those aren’t eggs! They’re spiderlings,” says . The two entomologists may just have moved a step closer to understanding one of the freshest mysteries in arachnid biology.

We’re in the Peruvian Amazon, seven hours upriver from Puerto Maldonado, the nearest town, in a small lab at the . It’s a cloudy, dark afternoon on the last day of May, and electricity won’t be turned on for another few hours. Outside, two capuchin monkeys are sitting in a palm tree and stuffing yellow fruit into their guilty-looking faces. Pairs of scarlet macaws swoop through the trees where earlier in the day a family of howler monkeys had chewed leaves.

Inside the open-air lab, there is a stench from the rotting apple that Reeves and Pomerantz – both graduate students at the University of Florida in Gainesville – use as bug-bait. Small vials filled with various critters are arrayed on the table – one with gliding ants, another with a wood-boring beetle, and others with more clumps like the one Reeves has been teasing apart.

These clumps are the handiwork of a strange species of spider that builds big, spider-shaped structures in its web using jungle debris and insect parts. Discovered less than two years ago along a trail near the lab, the spiders are presumed to be a new species in the genus Cyclosa – . Reeves and Pomerantz are here to find out why spiders in this particular species have apparently taken to arranging that debris into larger-than-life effigies of themselves.

Predator defence

The weather has not been kind, but the biologists have still managed to confirm a few things. For instance, they have found that the spiders prefer to operate in dense, shady underbrush. This preference for poorly lit places, Reeves says, supports a hypothesis explaining the purpose of the spider-shaped structures: predator defence.

Helicopter damselflies specialise in plucking orb-weaving spiders from their webs. Normally, damselflies are looking for spiders the size of the sculptors – between 3 and 6 millimetres. Reeves says it is possible that they are evading the damselflies by building decoys of larger, less appetising spiders. “We will eventually test that,” he says.

That’s just one mystery, though. Since the spiders were first discovered in the Peruvian Amazon in 2012, similar decoy-builders have popped up in Madagascar, spotted by a film crew; Reeves has also observed a similar species in the Philippines. Could the decoy-building behaviour, documented in forests separated by wide oceans and continents, have evolved independently? “I’ll be curious to see who their common ancestor is,” Reeves says. “This group is so diverse that very little is known about individual species.”

And then there are those spiderlings. As Reeves moved through the floodplain trails and stared at the spider impostors, he began to suspect that the individuals crafting the decoys were all females. But his photographs tell a different story: both sexes are hard at work crafting the decoys. “It’s curious,” Reeves says. “If the males are making webs, how do they meet females?” And, as he has found, the females’ decoys apparently double as spiderling nurseries. It’s not unusual for spiders to stash egg sacs in web debris, but the spiderlings don’t normally stick around for long after hatching.

Back in Florida, Reeves plans to feed his photographs into a software program and work out which decoy shapes appear most frequently in the humid, Tambopata forests. Sure, there are the many-legged ones that truly resemble spiders. But there are also handfuls of decoys that look more like stick figures or droopy cephalopods.

When he gets permission from the Peruvian government, he wants to grab a specimen and publish a formal description. “We don’t know anything about this spider other than it makes decoys,” Reeves says.

When over a thousand starving sea lion pups washed up on the southern California coast last year, nobody could explain it. A picture of the causes is now emerging, and it looks like sea lions might face a similar fate this year.

By this time last year 1300 California sea lion pups had been stranded alive – roughly four times as many as normal. While rehabilitation centres rescued as many as possible, the strandings were declared an “unusual mortality event” by the .

The cause has been a mystery, but one contributing factor has now been found: the sea lions’ , scientists from NOAA reported at a press conference on Monday.

have shown that over the last 15 years, high-fat sardines have moved farther from shore, and their numbers are declining. This year’s annual spring survey reported very few sardines along the California coast, says Sam McClatchie of NOAA’s Southwest Fisheries Science Center in La Jolla.

Vanishing sardines

“We don’t know whether that’s because they have temporarily disappeared, as sometimes these fish do, or whether they’ve moved out of our survey area,” McClatchie says.

He suspects that the long-term shift is caused by ocean currents that have pushed waters suitable for sardine spawning further from the coast.

Without their normal diet of high-fat sardines, some sea lion mothers were unable to adequately feed their pups. In an attempt to survive, the pups weaned early and struck out on their own. When the ocean proved too formidable a challenge, the exhausted animals hauled themselves onto California’s beaches, according to several biologists contacted by 51¶ŻÂţ.

Stranded pup numbers are high again this year, albeit lower than last year. Already, 650 have been sent to rehabilitation centres – more than twice the normal number for this time of year, NOAA reported during the press conference. NOAA is now investigating whether this year’s strandings are linked to those last year.

Pathogen link?

Sardine movement might only be one part of the story. Sea lions are opportunistic feeders and their other prey species are flourishing. As a result, some are hesitant to point too strongly at shifting sardines as the culprit. “You shouldn’t get too fixated on the idea that all they’re feeding on is sardines, because that’s not correct,” McClatchie says.

However, alternative food sources – such as squid and rockfish – are less nutritious, and may not be fatty enough to sustain some of the lactating mothers and their pups.

McClatchie and others think a number of factors combined to cause the fatalities. One of them may be the enormous size of the California sea lion population – it could be nearing the maximum number the habitat can support, and small perturbations in food supply could cause major ripples.

In addition, several pathogens were detected in last year’s stranded pups. “We don’t think they were the cause of the unusual mortality event, but they might have contributed to the severity of the impact,” says Sarah Wilkin, coordinator of NOAA’s .

What does seem clear is that California’s sea lions are headed for a rough stretch. There are predictions that an outbreak of bacterial leptospirosis could hit the population later this year, something that tends to happen every three to five years. And a looming El Niño could bring more disruption to the food supply later this year. In the past, El Niño years have seen the highest numbers of sea lion deaths and strandings.

IT IS after dark, and I’m 2 metres away from a snarling mountain lion. We are in the mountains above Santa Cruz, California, across the road from a prison work camp. The lion – a young male – pauses in his pacing only to hiss at us. Filling the air is the powerful aroma of the half-eaten deer carcass that lured him into captivity.

“It’s creepy out here,” observes my guide, wildlife ecologist Chris Wilmers from the University of California, Santa Cruz. We retreat a short distance to let the animal calm down.

Since 2008, Wilmers and his team of wranglers have been capturing the elusive animals (otherwise known as pumas, cougars and panthers, or more formally Puma concolor). They fit them with collars equipped with GPS transmitters that relay their location, and other instruments that record what they are up to, moment by moment – then let them go.

The data should reveal how pumas adapt to life in a habitat fragmented by roads, dotted with houses, and surrounded by water and concrete. This information can later be put to use by conservationists planning open spaces for the animals, or wildlife corridors they can use to travel safely. Though California’s mountain lions are not endangered, the population is small enough that geographic barriers could lead to reductions in genetic diversity and ultimately population decline.

“The long-term prognosis is not very good if they’re not interbreeding with other populations,” Wilmers says. He points to the Florida panther as a classic case of inbreeding’s harmful effects. “They’ve got a population of 80 or so individuals, and they are starting to have all these genetic defects like single testicles and infertile animals.” Using DNA from captured mountain lions, he plans to analyse gene flow in the population.

The techno-blinged collars are essential to understanding the lives of these nocturnal and notoriously shy animals. “They’re professionally secretive. They kill by being able to sneak up on things,” says Paul Houghtaling, the team’s primary field biologist.

“Right now, biologists are limited to knowing where animals are, but they don’t know what they’re doing,” Wilmers says. Successful conservation efforts depend on understanding the connection between an animal’s behaviours and its habitats.

The collars contain magnetometers, which act like tiny magnetic compasses and so reveal which direction a mountain lion is facing. They also carry accelerometers – similar to the devices in iPhones – which record speed and movement in three dimensions 64 times each second.

This generates distinct signatures for different kinds of activities. “If the animal is walking, every time the foot hits the ground it’s going to send a little jolt through the skeleton, and that will show itself in the data,” Wilmers says. “If the animal is running, every time it hits the ground, it’s going to really spike. If it turns its head, we’ll know which direction it is looking.”

Earlier that day, Houghtaling and I were on the trail of three pumas: a female called 2F and her two male cubs. At nearly 2 years old, 2F’s cubs are ready to leave their mother. The fact that they haven’t done so intrigues the team, but it gives them a chance to collar the youngsters before they disperse.

We download 2F’s location data, and searching in the woods stumble across a freshly killed, half-eaten deer. A fresh kill means the lions will likely return in the evening. We use the carcass to bait two 2-metre-long cage traps which we camouflage, then go home to wait.

At 8.30 pm I get a call saying we have a catch. Inside the cage is one of 2F’s cubs, called 9M. He is wearing the green ear tag he acquired when he was caught as a kitten. Field personnel sedate him and get to work measuring vital signs and taking blood, and measuring details such as paw width and tooth length. Finally, the collar goes on.

In another hour, 9M will be up and stumbling around. Though he weighs 45 kilograms, “he’s got a lot of bulking up to do before he’s big and savvy enough to play king of the hill with a resident male”, Houghtaling says. A team member will stay with him till he is fully alert, to make sure he doesn’t wander onto a road. After that it’s up to him. The puma project has another participant.

There’s a postscript to my night in the mountains. Two weeks later, 9M does the adolescent thing and leaves his mother. He has recently killed a deer, a raccoon and a snake. “Not sure what he was doing with the snake,” Houghtaling says.