Tag Archives: #spiders

Jumping Spiders Can Distinguish Living Objects From Non-living Ones Based On Their Movement (Biology)

Add this to the list of real-life spidey senses: Harvard researchers have shown that jumping spiders are able to tell the difference between animate objects and inanimate objects — an ability previously known only in vertebrates, including humans.

Using a specialized treadmill system and a point-light display animation, the team of scientists found that these spiders are able to recognize biological motion. This type of motion refers to the visual movements that come from living organisms when they are moving. The visual cue is how people, even babies, can tell someone is another person just by the way their bodies move. Many animals can do this, too.

The ability, which is critical for survival, is evolutionarily ancient since it is so widespread across vertebrates. The study from the Harvard team is believed to be the first demonstration of biological motion recognition in an invertebrate. The findings pose crucial questions about the evolutionary history of the ability and complex visual processing in non-vertebrates.

“[It] opens the possibility that such mechanisms might be widespread across the animal kingdom and not necessarily related to sociality,” the researchers wrote in the paper, which published in PLOS Biology on Thursday.

The study was authored by a team of researchers who were John Harvard Distinguished Science Fellows during the time of the study or are current fellows. Massimo De Agrò, now a researcher at an animal comparative economics lab in Regensburg, Germany, led the work. Paul Shamble, a current fellow, and Daniela C. Rößler, and Kris Kim, former fellows, co-authored the study.

The researchers chose jumping spiders to test biological motion cues because the animals are among the most visually adept of all arthropods. With eight eyes, for example, vision plays a central role in a wide range of behaviors.

They placed the jumping spiders, a species called Menemerus semilimbatus, into a forced choice experiment. They suspended the spiders above a spherical treadmill so their legs could make contact with it. The spiders were kept in a fixed position so only its legs could move, transferring its intended direction to the sphere which spun freely because of a constant stream of compressed air shooting up below it.

(Friendly disclaimer: No spiders were harmed during the experiment and all were freed in the same place they were captured afterwards.)

Once in position, the spiders were presented two animations as stimuli. The animations were called point-light displays, each consisting of a dozen or so small lights (or points) that were attached to key joints of another spider so they could record its movements. The body itself is not visible, but the digital points give a body-plan outline and impression of a living organism. In humans, for example, it only takes about eleven dots on the main joints of the body for observers to correctly identify it as another person.

For the spiders, the displays followed the motion of another spider walking. Most of the displays gave the impression of seeing a living animal. Some of the displays were less real than others and one, called a random display, did not give the impression it was living.

The researchers then observed how the spiders reacted and which light display they turned toward on the treadmill. They found the spiders reacted to the different point-light displays by pivoting and facing them directly, which indicated that the spiders were able to recognize biological motion.

Curiously, the team found the spiders preferred rotating towards the more artificial displays and always toward the random one when it was part of the choice. They initially thought they would turn more toward the displays simulating another spider and possible danger, but the behavior made sense in the context of jumping spiders and how their secondary set of eyes work to decode information.

“The secondary eyes are looking at this point-light display of biological motion and it can already understand it, whereas the other random motion is weird and they don’t understand what’s there,” De Agrò said.

The researchers hope to look into biological motion recognition in other invertebrates such as other insects or mollusks. The findings could lead to greater understanding of how these creatures perceive the world, De Agrò said.

Featured image: karthik photography / Getty Images

Reference: De Agrò M, Rößler DC, Kim K, Shamble PS (2021) Perception of biological motion by jumping spiders. PLoS Biol 19(7): e3001172. doi:10.1371/journal.pbio.3001172

Provided by Harvard University

Trinity Researchers Tackle the Spiders From Mars (Planetary Science)

Researchers at Trinity College Dublin have been shedding light on the enigmatic “spiders from Mars”, providing the first physical evidence that these unique features on the planet’s surface can be formed by the sublimation of CO2 ice.  

Spiders, more formally referred to as araneiforms, are strange-looking negative topography radial systems of dendritic troughs; patterns that resemble branches of a tree or fork lightning. These features, which are not found on Earth, are believed to be carved into the Martian surface by dry ice changing directly from solid to gas (sublimating) in the spring.  Unlike Earth, Mars’ atmosphere comprises mainly CO2 and as temperatures decrease in winter, this deposits onto the surface as CO2 frost and ice.

The Trinity team, along with colleagues at Durham University and the Open University,  conducted a series of experiments funded by the Irish Research Council and Europlanet at the Open University Mars Simulation Chamber (pictured below), under Martian atmospheric pressure, in order to investigate whether patterns similar to Martian spiders could form by dry ice sublimation.

Its findings are detailed in a paper published today in the Nature Journal Scientific Reports: “The Formation of Araneiforms by Carbon Dioxide Venting and Vigorous Sublimation Dynamics Under Martian Atmospheric Pressure”.

Dr Lauren McKeown drilling holes in the iceblocks for the project © TCD

Dr Lauren McKeown, who led this work during her PhD at Trinity and is now at the Open University, said:  

“This research presents the first set of empirical evidence for a surface process that is thought to modify the polar landscape on Mars. Kieffer’s hypothesis [explained below] has been well-accepted for over a decade, but until now, it has been framed in a purely theoretical context. … The experiments show directly that the spider patterns we observe on Mars from orbit can be carved by the direct conversion of dry ice from solid to gas.  It is exciting because we are beginning to understand more about how the surface of Mars is changing seasonally today.” 

The research team drilled holes in the centres of CO2 ice blocks and suspended them with a claw similar to those found in arcades, above granular beds of different grain sizes. They lowered the pressure inside a vacuum chamber to Martian atmospheric pressure (6mbar) and then used a lever system to place the CO2 ice block on the surface 

They made use of an effect known as the Leidenfrost Effect, whereby if a substance comes in contact with a surface much hotter than its sublimation point, it will form a gaseous layer around itself. When the block reached the sandy surface, CO2 turned directly from solid to gas and material was seen escaping through the central hole in the form of a plume 

In each case, once the block was lifted, a spider pattern had been eroded by the escaping gas. The spider patterns were more branched when finer grain sizes were used and less branched when coarser grain sizes were used.  

This is the first set of empirical evidence for this extant surface process.

Dr Mary Bourke, of Trinity’s Department of Geography, who supervised the Ph.D research, said:

“This innovative work supports the emergent theme that the current climate and weather on Mars has an important influence not only on dynamic surface processes, but also for any future robotic and/or human exploration of the planet.” 

The main hypothesis proposed for spider formation (Kieffer’s hypothesis) suggests that in spring, sunlight penetrates this translucent ice and heats the terrain beneath it. The ice will sublimate from its base, causing pressure to build up and eventually the ice will rupture, allowing pressurised gas to escape through a crack in the ice. The paths of the escaping gas will leave behind the dendritic patterns observed on Mars today and the sandy/dusty material will be deposited on top of the ice in the form of a plume.  

However, until now, it has not been known if such a theoretical process is possible and this process has never been directly observed on Mars.  

Additionally, the researchers observed that when CO2 blocks were released and allowed to sublimate within the sand bed, sublimation was much more vigorous than expected and material was thrown all over the chamber. This observation will be useful in understanding models of other CO2 sublimation-related processes on Mars, such as the formation of lateral Recurring Diffusive Flows surrounding linear dune gullies on Mars. 

The methodology used can be refocused to study the geomorphic role of CO2 sublimation on other active Martian surface feature formation – and indeed, can pave the way for further research on sublimation processes on other planetary bodies with no/scant atmospheres like Europa or Enceladus.

Featured image: An image from NASA’s Mars Reconnaissance Orbiter, acquired May 13, 2018 during winter at the South Pole of Mars, shows a carbon dioxide ice cap covering the region and as the sun returns in the spring, “spiders” begin to emerge from the landscape. © TCD

Reference: Mc Keown, L., McElwaine, J.N., Bourke, M.C. et al. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric pressure. Sci Rep 11, 6445 (2021). https://doi.org/10.1038/s41598-021-82763-7

Provided by Trinity College Dublin

Spiders In Space: Without Gravity, Light Becomes Key to Orientation (Astronomy)

Humans have taken spiders into space more than once to study the importance of gravity to their web-building. What originally began as a somewhat unsuccessful PR experiment for high school students has yielded the surprising insight that light plays a larger role in arachnid orientation than previously thought.

A specimen of the spider species Trichonephila clavipes on board the international space station ISS. (Photo: BioServe Space Technologies, University of Colorado Boulder

The spider experiment by the US space agency NASA is a lesson in the frustrating failures and happy accidents that sometimes lead to unexpected research findings. The question was relatively simple: on Earth, spiders build asymmetrical webs with the center displaced towards the upper edge. When resting, spiders sit with their head downwards because they can move towards freshly caught prey faster in the direction of gravity.

But what do arachnids do in zero gravity? In 2008, NASA wanted to inspire middle schools in the US with this experiment. But even though the question was simple, the planning and execution of the experiment in space was extremely challenging. This led to a number of mishaps.

Two specimens from different spider species flew to the International Space Station (ISS) as “arachnauts,” one (Metepeira labyrinthea) as the lead and the other (Larinioides patagiatus) as a reserve in case the first didn’t survive.

The reserve spider escaped

The back-up spider managed to break out of its storage chamber and into the main chamber. The chamber couldn’t be opened for safety reasons, so the extra spider could not be recaptured. The two spiders spun somewhat muddled webs, getting in each other’s way.

And if that were not enough, the flies included as food reproduced more quickly than expected. Over time, their larvae crawled out of the breeding container on the floor of the case into the experimental chamber, and after two weeks covered large parts of the front window. After a month, the spiders could no longer be seen behind all the fly larvae.

This failure long nagged at Paula Cushing of the Denver Museum of Nature & Science, who participated in the planning of the spider experiment. When the opportunity for a similar experiment on board the ISS cropped up again in 2011, the researcher got Dr. Samuel Zschokke of the University of Basel involved to prepare and analyze the new attempt. This time, the experiment started with four spiders of the same species (Trichonephila clavipes): two flew to the ISS in separate habitats, two stayed on Earth in separate habitats and were kept and observed under identical conditions as their fellows traveling in space – except that they were exposed to terrestrial gravity.

The females were males

The plan was originally to use four females. But another mishap occurred: the spiders had to be chosen for the experiment as juveniles and it is extremely difficult to determine the sex of juvenile animals. In the course of the experiment, two of the spiders turned out to be males, which differ markedly in body structure and size from females of this species when fully grown. But finally there was a stroke of luck – one of the males was on board the space station, the other on Earth.

The arachnids spun their webs, dismantled them, and spun new ones. Three cameras in each case took pictures every five minutes. Zschokke, Cushing and Stefanie Countryman of the University of Colorado’s BioServe Space Technologies that oversaw the design and launch of the space flight certified habitats containing the spiders and fruit fly larvae and camera system to the International Space Station analyzed the symmetry of 100 spider webs and the orientation of the spider in the web using about 14,500 images.

It turned out that the webs built in zero gravity were indeed more symmetrical than those spun on Earth. Their center was closer to the middle and the spiders did not always keep their heads downwards. However, the researchers noticed that it made a difference whether the spiders built their webs in lamplight or in the dark. Webs built on the ISS in lamplight were similarly asymmetrical as the terrestrial webs.

Light as a back-up system

“We wouldn’t have guessed that light would play a role in orienting the spiders in space,” says Zschokke, who analyzed the spider experiment and published the results with his colleagues in the journal Science of Nature. “We were very fortunate that the lamps were attached at the top of the chamber and not on various sides. Otherwise, we would not have been able to discover the effect of light on the symmetry of webs in zero gravity.”

Analysis of the pictures also showed that the spiders rested in arbitrary orientations in their webs when the lights were turned off, but oriented themselves away – i.e. downwards – when the lights were on. It seems spiders use light as an additional orientation aid when gravity is absent. Since spiders also build their webs in the dark and can catch prey without light, it had previously been assumed that light plays no role in their orientation.

“That spiders have a back-up system for orientation like this seems surprising, since they have never been exposed to an environment without gravity in the course of their evolution,” says Zschokke. On the other hand, he says, a spider’s sense of position could become confused while it is building its web. The organ responsible for this sense registers the relative position of the front part of the body to the back. During construction of the web, the two body parts are in constant motion, so an additional orientation aid based on the direction of the light is particularly useful.

Reference: Samuel Zschokke, Stefanie Countryman, Paula E. Cushing, “Spiders in space – orb-web-related behavior in zero gravity”, Science of Nature (2020), doi: 10.1007/s00114-020-01708-8 http://doi.org/10.1007/s00114-020-01708-8

Provided by University of Basel

Environmental Factors Affect The Distribution Of Iberian Spiders (Biology)

Southern small-leaved oak forests are the habitats with a higher level of spider endemism in the Iberian Peninsula, according to an article published in the journal Biodiversity and Conservation. The study analyses the factors that affect biodiversity patterns of spider communities in the national park network of Spain, and explains the role of the environmental factors in the distribution of the biodiversity of this faunistic group in the peninsular territory.

The study led by the UB and IBRio reveals how environmental factors affect the distribution of biodiversity of spiders in the peninsular territory. ©Jagoba Malumbres-Olarte, University of the Azores (Portugal)

The study is led by Professor Miquel Arnedo, from the Faculty of Biology and the Biodiversity Research Institute (IRBio) of the University of Barcelona, and it counts on the participation of the experts Luis Carlos Crespo, Marc Domènec and Carles Ribera (UB-IRBio), Jagoba Malumbres-Olarte and Pedro Cardoso, from the University of the Azores (Portugal), and Jordi Moya-Laraño, from the Experimental Station of Arid Zones in Almeria (EEZA-CSIC).

Iberian spiders: how are they distributed throughout the peninsular territory?

There are many doubts on the biology and ecology of Iberian spider communities, a group with a fundamental role in natural ecosystems. There might be more than 1,400 species in the peninsular territory, which has a great climate diversity and natural habitat. In some cases, there are species with a limited distribution -regional or local endemism- and this would explain the observed changes among the communities of different areas.

The new study focuses on the study of spider communities in the national parks of Aigüestortes i Estany de Sant Maurici, Ordesa y Monte Perdido, Picos de Europa, Monfragüe, Cabañeros and Sierra Nevada. In particular, they studied the spider communities -a total of 20,552 specimens from 375 species- in different types of oak trees (Quercus spp), widely distributed around the peninsula, such as those that include the sessile oak (Quercus petraea), the Valencian oak (Quercus faginea) and the Pyrinean oak (Quercus pyrenaica).

“The results reveal that Valencian oak forests (Q. faginea) are those with a higher number of spider species, probably due to the combined effects of the physical structure of the habitat and climate conditions”, notes Professor Miquel Arnedo, from the Department of Evolutionary Biology, Ecology and Environmental Sciences.

The study also confirms the previous studies that point to a decrease of species in southern forest ecosystems, which is caused by the reduction of connectivity of ecosystems with the rest of the continent.

“However, we suggest that these changes in the number of species could be the result of complex interactions between the geographical position, habitat and local climate. This would make it possible, for instance, for us to find spider communities in the Cabañeros National Park (Castilla – La Mancha) with a higher number of species than in Picos de Europa (Asturias)”, notes Arnedo.

Climate, geography and endemism of Iberian spiders

Another relevant contribution of the study is the identification of a pattern that relates the increase of the level of endemism in the spider communities with the rise of temperatures and decrease of annual precipitation, which are typical from the Mediterranean climate.

“Spider communities in Mediterranean areas seem to be more endemic -when we consider distributions of all species in each community- and have a higher number of exclusively Iberian species”, notes the expert Jagoba Malumbres-Olarte, first signatory of the article. Other groups of spiders show a higher level of endemism depending on certain ecological features, according to the authors.

“In this case, we saw that those spiders that spread more frequently through the air using silk, known as ballooning, show a more extensive geographical distribution and therefore, are less endemic. For instance, this would be the case of some species from the Lindyphiidae family”.

Spiders, indicators of environmental quality

Despite the ecological value of spiders, these arthropods have been rarely used as bioindicators. This study sheds light in this field of ecology studies, and suggests that the presence and abundance of spider families with high levels of endemism -for instance, Oonopidae, Dysderidae, Zodariidae and Sparassidae families- could be used by researchers as indicators of the singularities and ecological qualities of some natural areas.

“In the studied communities, these families are those with a higher level of endemism. If we consider the difficulty when identifying certain Iberian species and the likelihood to find undescribed species, the option of using spider families -instead of species- could ease the use of spiders as ecological and conservation indicators”, authors say.

Improving biodiversity conservation strategies

The lack of many experts able to identify and describe spider species and the great diversity of this group are factors that make it difficult for researchers to study the ecology of Iberian spider communities, and by extension, many others. Expanding the knowledge on the biodiversity of the peninsular spider fauna requires the promotion of monitoring programs and a regular control of temporary changes in the communities.

In this context, the published article in the journal Biodiversity and Conservation brings new information to improve the conservation and management of national parks and protected areas in general. It reveals new data on the number and composition of species in the communities in the national parks, information that enables having a reference for future monitoring plans. Also, it identifies the most relevant groups depending on their endemic levels (that is, those with potentially high values for conservation).

“Our study also states that different habitats within the same area or park could have a differential value regarding conservation and scientific interest, and consequently, they could be an object of several levels of prioritization in conservation actions”, conclude the researchers.

References: Malumbres-Olarte, J., Crespo, L.C., Domènech, M. et al. How Iberian are we? Mediterranean climate determines structure and endemicity of spider communities in Iberian oak forests. Biodivers Conserv (2020). https://doi.org/10.1007/s10531-020-02058-7 https://link.springer.com/article/10.1007/s10531-020-02058-7

Provided by University of Barcelona

These Spiders Can Hear (Biology)

Ogre-faced spiders, named for their massive eyes, hide during the day and hunt by night, dangling from Florida palm fronds and casting silk nets on insects on the ground and in the air. In addition to their incredible night vision, these spiders also can hear their predators and prey, researchers report in the journal Current Biology on October 29. Having no ears, the spiders use hairs and joint receptors on their legs to pick up sounds from at least 2 meters away. The results suggest that spiders can hear low-frequency sounds from insect prey as well as higher frequency sounds from bird predators.

A frontal view of an ogre-faced spider, showing their large eyes. Credit: Jay Stafstrom.

“I think many spiders can actually hear, but everybody takes it for granted that spiders have a sticky web to catch prey, so they’re only good at detecting close vibrations,” says senior author Ron Hoy, professor of neurobiology and behavior at Cornell University. “Vibration detection works for sensing shaking of the web or ground, but detecting those airborne disturbances at a distance is the province of hearing, which is what we do and what spiders do too, but they do it with specialized receptors, not eardrums.”

Instead of passively waiting for prey to fall into a web and get stuck, ogre-faced spiders use their webs as a weapon. After spending the daylight hours completely still, blending in with the surrounding palmetto fronds, they emerge at night to dangle close to the ground and cast their webs like a net on unwary insects. While they use their keen night vision to catch prey on the ground, they can also catch insects in the air by performing an elaborately choreographed backwards strike, which does not seem to rely on vision.

“In a previous study, I actually put dental silicone over their eyes so they couldn’t see,” says first author Jay Stafstrom, a postdoctoral researcher in the Hoy Lab. “And I found that when I put them back out into nature, they couldn’t catch prey from off the ground, but they could still catch insects from out of the air. So I was pretty sure these spiders were using a different sensory system to hunt flying insects.”

While that study hinted that the spiders might be able to hear, this one showed just how well they can do it. By observing the spiders’ reactions to different tones and measuring their neural response with electrodes placed in the spiders’ brains and legs, the team determined that the spiders could hear sounds of up to 10 kHz in frequency, far higher than the sounds of a walking or flying insect.

“When I played low tone frequencies, even from a distance, they would strike like they were hunting an insect, which they don’t do for higher frequencies,” says Stafstrom. “And the fact that we were able to do that from a distance, knowing we’re not getting up close and causing them to vibrate. That was key to knowing they can really hear.”

Hearing these higher frequencies may not be helpful for hunting, but it may help them stay alert when hiding from their own predators.

The upside-down posture that ogre-faced spiders take when waiting for passing prey. Credit: Jay Stafstrom

“If you give an animal a threatening stimulus, we all know about the fight or flight response. Invertebrates have that too, but the other ‘f’ is ‘freeze.’ That’s what these spiders do,” says Hoy. “They’re in a cryptic posture. Their nervous system is in a sleep state. But as soon as they pick up any kind of salient stimulus, boom, that turns on the neuromuscular system. It’s a selective attention system.”

While these results make it clear that the spiders can detect sounds well, the researchers are next interested in testing their directional hearing—whether they can tell where sounds are coming from. If they can also hear directionally, this might help further explain their acrobatic hunting style.

“What I found really amazing is that to cast their net at flying bugs they have to do a half backflip and spread their web at the same time, so they’re essentially playing centerfield,” says Hoy. “Directional hearing is a big deal in any animal, but I think there are really going to be some interesting surprises from this spider.”

References: Stafstrom et al.: “Ogre-faced, net-casting spiders use auditory cues to detect airborne prey”, Current Biology, 2020. https://www.cell.com/current-biology/fulltext/S0960-9822(20)31418-4

Provided by Cell Press