Tag Archives: spiders

As autumn approaches here’s why we see more spiders in our houses and why wasps are desperate for sugar

Credit: Pixabay.

The tell-tale signs that autumn is here are clear to us; the days are getting shorter and the temperature is decreasing. We take this as a sign to pull out our winter woollies and think about turning on the radiators. But how do insects know that winter is coming? And what do they do to prepare?

Folklore has suggested over the years that insects and other invertebrates can predict the weather and that, for example, we could start to see bigger spider webs if the weather is going to get colder. The evidence for those bigger webs ahead of bad weather is weak. But there certainly are changes in insect behaviour we can see at this time of year, and it shows they are predicting changes they need to make as the weather changes.

Insects are extremely sensitive to changes in the environment and change in light is the main cue that insects use to signal the change in seasons. Insects, like humans, detect light with their eyes. But unlike humans insects have more than two eyes. In addition to the two big compound eyes that they have on the front of their heads most insects also have three smaller eyes on the top of their heads called ocelli. Light information is passed from their eyes to the brain and interpreted by an internal clock to detect the changing seasons, which may also be important in humans and other primates.

Responding to the changing seasons is really important for insects as they are cold blooded and can’t regulate their own body temperature. But insects have different ways of coping with the oncoming cold weather. Some, like the painted lady butterfly, leave the UK in autumn heading to north Africa where they breed. Others produce their own “antifreeze” proteins that allow them to cope with winter temperatures. However, the majority of insects undergo a slowing down process called diapause, where they essentially sleep for the winter. At this time of year these insects are looking for a sheltered place to spend the winter – and this is why we see more spiders in our houses at this time of year. You may also notice groups of insects, like ladybirds, huddled on windowsills and under rocks. These insects will stay protected over the winter and reawaken in spring.

Because of migration, diapause and the natural death of some insects at the end of the summer, you may generally feel there are fewer insects around than just a few weeks ago. But there are some new ones emerging that we didn’t see earlier in the summer. In the south you might spot the beautiful ivy bee which is only active when the ivy is in blossom. Autumn also brings the mass emergence of crane flies, which, although they look a bit like mosquitos, are actually harmless.

You also might notice more wasps visiting flowers to drink the sugary nectar – at this time of year they become very hungry for sugar. Wasps don’t really care where they get their sugar fix from and are just as likely to try and steal our sugary drinks as we are enjoying the last of the summer in our gardens or enjoying a walk. Their craving for sugar is actually really beneficial as their visits flower-to-flower, trying to satisfy their insatiable craving, lead them to pollinate flowers just like bees.

For me the most striking sign of autumn is the appearance of a lot of very large bumblebees out visiting the last flowers of the season.

These large bees are next year’s queens. After being born late in the summer season they mate and stock up on energy before finding a place to hibernate for the winter. When we see them again it’ll be an indicator that spring is on its way when the queens emerge from their sleep and make new nests.

This response to changing seasons and the fact that insects have been shown to change their behaviours, like mating, in response to impending rain leads to the assumption that insects are weather forecasters, predicting that rain is coming. However, it is more likely that they are just responding to the changes in weather, like people taking an umbrella with them when the skies are grey. But there is a lot of variation in how insects do respond to the weather and I, for one, will be sticking to the Met Office for my weather forecasts.The Conversation

Elizabeth Duncan, Associate Professor of Zoology, University of Leeds and Thomas Dally, Postdoctoral research fellow, University of Leeds

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Scientists engineer ‘daddy shortlegs’ to better understand spiders

Daddy longlegs can wrap their limbs around things and can go without food for months. Credit: Flickr, stanze.

Hate them or love them, daddy longlegs are perhaps the most widespread arachnids in the world, being present on all continents except Antarctica. Their extra-long limbs are unique among arachnids, but how did they get them? In a new study, researchers genetically modified some specimens by knocking down a pair of genes associated with leg development. In the process, they made daddy longlegs with short limbs. Basically, they made daddy shortlegs.

Though not exactly spiders, the daddy longlegs genome could unravel arachnid evolution

Daddy longlegs, also known as harvestmen, are not actually spiders. They are Opiliones, which are more closely related to scorpions than to spiders.

A few characteristics differentiate Opiliones from spiders. For starters, they just have two eyes. They cannot produce silk and therefore cannot make webs. They also lack venom glands. Spiders usually have two distinct body segments, while Opiliones have a compact oval-shaped body. It looks like one segment but the cephalothorax and abdomen are fused together so that the joint is hard to see. Finally, the tips of a harvestman’s limbs are flexible, allowing them to wrap around a twig like a monkey’s tail.

Nevertheless, scientists think that the genome of daddy longlegs could be key to unraveling the evolutionary history of spiders, which is why researchers led by Guilherme Gainett from the University of Wisconsin-Madison decided to embark on this study.

The scientists sequenced the genome of Phalangium opilio, one of the most common arachnids of more than 6,000 different species of daddy longlegs. Using RNA interference, a cellular mechanism that uses the gene’s own DNA sequence to turn it off, the team of researchers deactivated genes involved in leg development in hundreds of daddy longlegs embryos.

The embryo in the first picture from the left is a normal daddy longlegs, while the next two have been genetically modified by tweaking genes related to limb development. Credit: Proceedings of the Royal Society B.

The resulting genetically modified specimens developed six out of the critter’s eight legs with only about half the size of their normal counterparts. In fact, the legs don’t seem to be legs at all but rather a different kind of appendage, known as a pedipalp, which is used to handle food. But in the process, the daddy shortlegs also lost their tarsomeres, which allow them to grasp sticks.

These experiments, although they may seem gruesome and cruel, are important to deciphering the complex web of genetics and epigenetics that give rise to typical arachnid features, from a spider’s fangs to a scorpion’s pincers.

“We anticipate that the genome of P. opilio will facilitate the development of more sophisticated tools for functional genetics, toward refining the understanding of how daddy-long-legs make their long legs,” the authors wrote in the Proceedings of the Royal Society B.

Big-eyed spiders that cast nets like gladiators can hear prey despite lacking ears

Credit: Cornell University.

Ogre-faced spiders (Dinopsis spinosus) have massive eyes that grant them phenomenal night vision to hunt prey in the dark with their silk nets. It seems these skilled predators have yet another ace up their eight legs: very sensitive hearing.

Although they don’t have ears, these spiders have tiny hairs and join receptors on their legs that are sensitive enough to pick up sounds from at least 2 meters away, according to researchers at Cornell University.

“These spiders are wonderful creatures that have some fascinating behaviors, allowed by fine-tuned sensory systems very unlike our own. Sadly, these spiders are very overlooked, especially considering how impressive their sensory systems and behavior are. We’re hoping to establish a foundation for future work on these and other spiders in the realm of sensory ecology,” Jay Stafstrom, first author of the new study and a postdoc at Cornell University, told ZME Science.

The stick-like nocturnal predators are part of the net-casting family of spiders. Instead of waiting passively for prey to fall into a permanent web that they weaved earlier, ogre-faced spiders and other Dinopsis spiders throw a rectangular-shaped net over unsuspecting victims that pass by, sort of like gladiators.

In order to ensnare their prey, ogre-faced spiders are aided by their googly-looking eyes. But besides keen night vision, these spiders also perform elaborate backward strikes to catch their prey, which suggests that they have another sophisticated spidey sense.

Previously, Stafstrom and colleagues blindfolded ogre-faced spiders by placing dental silicone over their eyes. The blind spiders weren’t able to catch prey off the ground, but they could still hunt insects from out of the air. This was a huge hint that they employed other sensory systems in hunting besides vision.

For their new study, the researchers observed the spiders’ reactions to various tones by measuring their neural response with tiny electrodes placed in the spiders’ brains and legs. They found that the spiders could sense vibrations in the air of up to 10 kHz, much higher in frequency than the sounds produced by walking or flying insects.

This high-speed video shows the backwards strike of an ogre-faced spider. Credit: Sam Whitehead.

Stafstrom says that it’s difficult to compare the ogre-faced spider’s hearing with other animals, but he finds it “impressive that they can hear so well, at least in terms of speed and direction.”

“If you consider trying to catch an insect as it’s flying past you, in nearly complete darkness (as they are doing this at night), the act of snatching something with a small net would seem a pretty difficult feat. We suspect that hearing is fairly widespread across other spiders, but we haven’t been able to conduct the appropriate comparative study to really investigate how widespread this phenomenon is. The two types of sensors shown to detect sound in spiders (long hairs and the metatarsal organs) are possessed by most, if not all spiders,” the researcher told ZME Science.

Since the spiders would only need to detect low-frequency tones to snatch prey, the researchers believe that their ability to detect much higher frequency may be helpful in staying alert for signs of their own predators.

“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 senior author Ron Hoy, professor of neurobiology and behavior at Cornell University. “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.”

In the future, the researchers are interested in learning whether the spiders have directional hearing too, meaning whether they can tell where sounds are coming from. This would explain their impressive choreography while hunting and perhaps inspire a new generation of microphones.

“These spiders have evolved for millions of years to be really good at snatching things up with this net, and the sensory systems they possess are exquisite at allowing them to do so. Since these spiders have been adapting for so long to detect both visual and hearing information so well, it would be beneficial, as humans, to better understand how they do it. If we could truly understand how they detect and process environmental information, we would surely have some valuable insight that could be applied to creating more sensitive/accurate biosensors (like microphones) in ways that we have never imagined before. Looking at the ability of these spiders to detect the directional component of a sound is what we’re most interested in next – we expect these spiders are quite adept at determining the location of a sound source, and we’re interested in understanding exactly how good they are at it,” Stafstrom said.

The findings appeared in the journal Current Biology.

Spider-inspired double-sided tape could leave stitches in the past

Inspired on how spiders exude glue to catch their prey in the rain, a group of scientists at the Massachusetts Institute of Technology (MIT) has designed a double-sided tape which sticks to the body tissue after surgery.

Credit Wikipedia Commons

The team studied the way spiders’ secretion absorbed water in order to secure their next meal. The latest sticky tape also performs in the same manner and allegedly works within seconds, as proven by results during tests on pig skin and lungs.

The tape is proposed as an alternative to stitches. Tests from scientists at MIT found the tape worked within seconds on pig skin and lungs. However, it is several years from being ready to trial on humans and more research is needed.

One of the main chemicals used in medical adhesive can be toxic to humans, causing pain and inflammation around the area where it is used. Other surgical glues are made from water-based gels. These are less toxic but do not bond with the same strength, doctors have said in the past.

“There are over 230 million major surgeries all around the world per year, and many of them require sutures to close the wound, which can actually cause stress on the tissues and can cause infections, pain, and scars,” study author Xuanhe Zhao, a mechanical engineer at MIT, says in a statement. “We are proposing a fundamentally different approach to sealing tissue.”

Spiders are known to secrete a sticky material that contains polysaccharides. This absorbs water from the surface of an insect almost instantly, by thus leaving a small dry patch which can be used as a glue to stick to.

The team of researchers has similarly used polyacrylic acid on the tap which can further absorb water from wet body tissue and activate the glue in order to stick fast. By adding chitosan or even gelatin helps to keep the tape its shape for a couple of days or even for a month, depending upon how long it requires to last.

The team has tested the tape on different types of pig and rat tissues, including small intestine, liver, stomach, and skin. More tests on animals will be performed in the future, they claimed. The tape can also be used to stick medical devices to organs such as heart “without causing damage or secondary complications from puncturing tissue”.

Study author Hyunwoo Yuk commented on the research, published in Nature: “It’s very challenging to suture soft or fragile tissues such as the lung and trachea – but with our double-sided tape, within five seconds we can easily seal them.” It could potentially also be used to attach medical devices to organs such as the heart “without causing damage or secondary complications from puncturing tissue”.

Why you shouldn’t kill your spiders at home — according to scientists

I know it may be hard to convince you, but let me try: Don’t kill the next spider you see in your home.

He comes in peace. Matt Bertone, CC BY-ND.

Why? Because spiders are an important part of nature and our indoor ecosystem – as well as being fellow organisms in their own right.

People like to think of their dwellings as safely insulated from the outside world, but many types of spiders can be found inside. Some are accidentally trapped, while others are short-term visitors. Some species even enjoy the great indoors, where they happily live out their lives and make more spiders. These arachnids are usually secretive, and almost all you meet are neither aggressive nor dangerous. And they may be providing services like eating pests – some even eat other spiders.

My colleagues and I conducted a visual survey of 50 North Carolina homes to inventory just which arthropods live under our roofs. Every single house we visited was home to spiders. The most common species we encountered were cobweb spiders and cellar spiders.

Although they are generalist predators, apt to eat anything they can catch, spiders regularly capture nuisance pests and even disease-carrying insects – for example, mosquitoes. There’s even a species of jumping spider that prefers to eat blood-filled mosquitoes in African homes. So killing a spider doesn’t just cost the arachnid its life, it may take an important predator out of your home.Both build webs where they lie in wait for prey to get caught. Cellar spiders sometimes leave their webs to hunt other spiders on their turf, mimicking prey to catch their cousins for dinner.

It’s natural to fear spiders. They have lots of legs and almost all are venomous – though the majority of species have venom too weak to cause issues in humans, if their fangs can pierce our skin at all. Even entomologists themselves can fall prey to arachnophobia. I know a few spider researchers who overcame their fear by observing and working with these fascinating creatures. If they can do it, so can you!

An arachnologist’s story of growing up terrified of spiders but ultimately becoming fascinated by them.

Spiders are not out to get you and actually prefer to avoid humans; we are much more dangerous to them than vice versa. Bites from spiders are extremely rare. Although there are a few medically important species like widow spiders and recluses, even their bites are uncommon and rarely cause serious issues.

If you truly can’t stand that spider in your house, apartment, garage, or wherever, instead of smashing it, try to capture it and release it outside. It’ll find somewhere else to go, and both parties will be happier with the outcome.

The ConversationBut if you can stomach it, it’s OK to have spiders in your home. In fact, it’s normal. And frankly, even if you don’t see them, they’ll still be there. So consider a live-and-let-live approach to the next spider you encounter.

Matt Bertone, Extension Associate in Entomology, North Carolina State University

This article was originally published on The Conversation. Read the original article.

Common spiders living in your house

Spiders are extremely common around the house. Although many people are afraid of spiders, these critters really shouldn’t be feared. Most indoor spiders have webs in a secluded corner and won’t bother you unless directly provoked. But they will catch mosquitoes and flies for you — it’s organic pest-control!

Most common household spider species are very flexible about what they eat and where they live, so they can survive in lots of different environments and continents. Here are some of the most common household species so you can try to identify your roommates.

The American house spider

The American house spider (Parasteatoda tepidariorum) is known as the house spider in the USA because it is the most common household spider species. These spiders are about 4/5 cm (1/4 inch) long. They are brown with some black or white spots on the abdomen. They produce distinctive egg sacks that are shaped like a teardrop with a papery brown exterior. House spiders will only bite humans when directly provoked. This species is found around the whole world and usually in or near man-made structures. House spiders build messy cobwebs in the corners of rooms and in sheds and barns. They mostly eat flies, mosquitoes, ants, and wasps.

The American house spider is a very common species in houses. Image credits: Géry Parent

The domestic spider

The domestic spider (Tegenaria domestica) is also known as the house spider in Europe. Domestic spiders have mottled bodies, often with a chevron pattern on their abdomens. They make a messy funnel shaped web built around a flat surface, with the spider waiting at the bottom of the funnel. Small to mid-size insects are usually the prey of choice. Domestic spiders are not aggressive and will often back off to their web when confronted. If the web is attacked, the spiders will flee or huddle in a ball. Males are known to get stuck in bathtubs and sinks at night. Domestic spiders are not known to bite often, but even if they do it is painless. These spider has also spread everywhere through human transport; they are found across Europe, North America, and parts of Western Asia.

There’s a European house spider in the bath! Image credits: Sanchom

The cellar spider

Cellar spiders (in the Pholcidae family), are often confused with daddy longlegs the Opiliones (read explanation here) due to their long thin legs. However, cellar spiders have 6-8 eyes and two distinct body segments. They are often found in dark, isolated places as basements, attics, and cellars. In the wild, they build webs under logs and in caves. They set up in a corner and build a messy 3-D web. The threads in the web are not sticky, but when something flies into it they vibrate and the spider appears quickly to grab and wrap its prey in silk. Cellar spiders eat insects, arachnids, and other small vertebrates; they are especially fond of ants. These spiders can survive months without eating.

They are also found on every continent except Antarctica, from deserts to tropical forests. In particular, the species Pholcus phalangioides likes living in houses and has been spread around the world through human movement. All of the species are harmless; they don’t bite often and are not known to cause any harm to humans.

Cellar spiders generally stay in their web and can go without food for months. Image credits: stanze

Daddy longlegs

A special mention on this list is are daddy longlegs, also known as harvestmen. They are actually not spiders; they are arachnids more closely related to scorpions than to spiders. Daddy longlegs belong to the Opilione order. They have a compact oval body (no distinct segments), two eyes, and eight thin long legs. They don’t have any venom glands so they are completely harmless. Daddy longlegs are common around the house and outside. Opiliones scavenge food to eat, including dead insects or food waste, and prey on everything from aphids to spiders. They are found on every continent except Antarctica, and can live in many different types of habitats such as forests, meadows, caves, and wetlands.

Daddy longlegs are distinguishable from spiders with their compact body and two eyes. Image credits: Luke

Black widows

Black widows (Lactrodecus genus) are considered the most venomous spiders in North America, but they only bite when disturbed. Most victims aren’t in serious danger — death by black widow is extremely rare; very old, young, and sick victims are the most at risk. Female black widows are a shiny black color with a distinctive red hourglass shape on the underside of the abdomen. Males are a dark grey or brown color; they sometimes have red or pink spots on their backs. The female spider’s poison is 3 times stronger than that of the males; it’s lucky that the females are very easy to recognize!

Black widows occupy dark dry shelters in trash, garages, basements, and sheds. They are found in temperate regions throughout the world, in North and South America, Southern Europe and Asia, Australia, and Africa. They eat flies, grasshoppers, mosquitoes, beetles, and caterpillars. The spiders wrap their prey in silk and insert digestive enzymes into the package to enjoy a liquid lunch.

Female black widows are easily recognizable by the red hourglass shape on their abdomen. Image credits: skeeze

Jumping Spiders

Jumping spiders (Salticidae family) are mostly found outdoors but can also find their way under furniture, below doors, between shelved books, and in the folds of fabrics. They are recognizable by their square-shaped heads, compact body, and two very large eyes (plus 6 smaller ones). They have the best vision of any spider; these little spiders can see up to 20 cm (8 inches) away! Jumping spiders are named as such because they can jump many times their body length to catch prey; they are active hunters. They eat insects, arthropods, and even nectar. One species in Africa specifically targets mosquitoes that transmit malaria parasites, helping in malaria prevention. They do not build webs and instead use silk to communicate and build “pup tents” where they shelter and overwinter. Their bites are harmless unless you’re specifically allergic.

My, what big eyes you have. Image credits: Thomas Shahan

There you have it— the most common house spiders in the world!

No web, no worries — spiders also like to eat vegetarian

Spiders’ diets aren’t limited to juicy insect bits; they’ve been shown to occasionally consume fish, frogs or even bats before — but they spice up their menus with vegetarian courses too, zoologists from the US and UK have found.

Young jumping spider consuming a Beltian body (lipid and protein-rich detachable leaflet tips of acacias.)
Image credits Eric J. Scully/ Harvard University.

Spiders are traditionally viewed as insectivorous predators, dining on anything their webs can trap. But scientists are becoming increasingly aware that’s a skewed view of them, and that their diet is more diverse than we imagine. If available, spiders won’t shy away from eating fish, frogs, bats — all kinds of meat. But a team of zoologists from the University of Basel, Brandeis University and Cardiff University has now brought evidence of meat-eating spiders chowing down on plant-based foods too.

“The ability of spiders to derive nutrients from plants is broadening the food base of these animals; this might be a survival mechanism helping spiders to stay alive during periods when insects are scarce”, says lead author Martin Nyffeler from the University of Basel in Switzerland.

They gathered and documented all examples of spiders eating such items from scientific literature they could find. Their collection of data shows that spiders from ten families have been reported feeding on a wide range of plants such as trees, shrubs, ferns, flowers, weeds or grasses. And they aren’t picky, either; they’ll eat anything from nectar, sap or honeydew to leaves, pollen and seeds.

Jumping spider drinking nectar at extrafloral nectaries of a shrub.
Image credits David E. Hill, Peckham Society, South Carolina.

A family of diurnal spiders, the Salticidae, seem to be the most voracious plant-eaters of the Araneae order. These plant-dwelling, highly mobile foragers were attributed with almost 60 percent of the incidents documented in this study.

But such feeding habits aren’t a Salticidae-only thing. Plant-eating in spiders has been reported from all continents except Antarctica, but seems to be more common in warmer areas of the globe. As a larger number of the reports relate to nectar consumption (which has its core distribution in warmer areas where plants secreting large amounts of nectar are widespread) this isn’t too surprising.

“Diversifying their diet with plant is advantageous from a nutritional point of view, since diet mixing is optimizing nutrient intake,” Nyffeler concludes.

Currently, the extent to which different categories of plant-based food contribute to the spiders’ diet is still largely unexplored. But, as there currently is a known species of spider that is mostly herbivorous, the Central America indigenous Bagheera kiplingi, it can be assumed that in a pinch spiders can live on a full veggie diet for some time.

The full paper, titled “Plant-eating by spiders” has been published online in the Journal of Arachnology and can be read here.


Insect homosexuality just a case of mistaken identity


Some of you might find it surprising to hear that a lot of animals engage in homosexual behavior.  Close to 1,500 species, ranging from primates to gut worms, have been observed engaging in such behavior and this is well documented for 500 of them. No one comes close to insects and spiders, though, which have a significantly larger homosexual/hetero ratio out of all animals. Biologists and animal behaviorists have attempted to explain this proposing various theories, but lack of evidence has failed to substantiate any of these. A recent study found insect homosexuality, though still the result of an adaptive trait, can be explained and supported though a very simple explanation: it’s just a case of mistaken identity.

Deep in the Amazon jungle, a tarantula gently oversees from the comfort and safety of a Brazilian nut tree. When suddenly…

“Hey! Do you mind?” 

“What? You’re not into me?”

“I’m a DUDE, man!”

“Sorry, sorry… I thought you were a female,  bro. Ishhh…. you know these things happen often”

Now, some of you might find this kind of explanation unrealistic, but it does make sense after you read on. In birds and mammals, homosexual behavior (sexual activity, courtship, affection, pair bonding, and parenting among same-sex animal pairs) has been shown to have evolutionary benefits. It provides “practice” for young adults, means of disposing of old sperm, discourages predators, distracts competitors. and maintains alliances within groups. Biologists have tried to explain homosexual behavior in insects and spiders arguing the same benefits seen in other animals engaging in homosexual behavior applies to them as well.

[RELATED] The weird world of animal sex

After studying 110 species of spiders and insects, Dr. Inon Scharf of Tel Aviv University’s Department of Zoology and Dr. Oliver Martin of ETH Zurich have found that homosexual behavior in bugs is probably accidental in most cases, though.

When studying behaviorism it’s important to put costs and benefits into balance to filter out unfounded hypotheses. In general there is no clear benefit to homosexual behavior in insects, however its cost is just as large as heterosexual behavior – expending sperm, wasting time that could go toward other activities, and boosting the risk of injury, disease, and predation. Heterosexuality has one definite benefit and advantage over homosexuality, though – procreation. Despite this, in some species, up to 85 percent of males engage in homosexual behavior.

There are no clear benefits to homosexuality and the costs are just as high as heterosexuality. The only viable explanation, considering the high count, is that insects and spiders mistake males for females when mating. Why? In some cases, males carry around the scents of females they have just mated with, sending confusing signals to other males. In other cases, males and females look so similar to one another that males cannot tell if potential mates are female until after they have mounted them. And there are other things as well, but really why is it so hard for insects to discriminate genders? Again, it all comes to cost.

Waiting for too long to discriminate if the potential mate in front of you is male or female may translate into a lost opportunity. In other words, the risk of mating with a peer of the same sex is canceled by the more undesirable risk of missing a procreating mate. This explanation is supported by the fact that many species that exhibit homosexual behavior also mate with related species or inanimate objects, like beer bottles—indicating a general tendency toward misidentification. And this might not be all there is to insect and spider homosexuality.

“Homosexual behavior may be genomically linked to being more active, a better forager, or a better competitor,” says Dr. Schart. “So even though misidentifying mates isn’t a desirable trait, it’s part of a package of traits that leaves the insect better adapted overall.”

The findings were reported in the journal Behavioral Ecology and Sociobiology.


How spiders can fly for miles: electrostatic launching


Silk flows from a spiny-backed spider. Kunkel Microscopy, Inc./Visuals Unlimited, Inc./Corbis

In a mind boggling act, spiders are capable of “ballooning” themselves using silk strands and fly for miles, both in altitude and distance. Small and big spiders alike can do this, although smaller ones are capable of traveling further, and scientists have long theorized the mechanisms of spider ‘flight’. Peter Gorham at the University of Hawaii tested a theory that dates back from the early 1800s, first proposed by Charles Darwin himself, which states that the spiders achieve their amazing lift through electrostatic means. His findings support this theory, explaining the mysterious and peculiar spider flight behavior which has puzzled scientists for so long.

While off the cost of Argentina a few tens of miles away sailing in the infamous HMS Beagle in the 1830s, Darwin perplexedly recalled how the ship was flooded with spiders as if they had dropped from the clouds.

“I repeatedly observed the same kind of small spider, either when placed or having crawled on some little eminence, elevate its abdomen, send forth a thread, and then sail away horizontally, but with a rapidity which was quite unaccountable.”  C. Darwin.

At the time Darwin thought spiders used their silk to catch thermal air currents to carry them to considerable height, and this conventional wisdom was used to explain it for years. Darwin also proposed  “electrostatic repulsion” played a role in the fanning of the threads, but this theory was dismissed by biologists in favor of the thermal air currents theory.

Launching spiders  several miles up high

Hot air doesn’t account for a number of anomalies, however.  How can these spiders launch themselves with a surprisingly high velocity even when there is little or no wind; how do thermal currents lift heavy adult spiders of up to 100 milligrams; and when spiders release several threads, why do these threads form a fan-shape as if repelling each other?

Gorham re-examined the electrostatic theory and says that it can easily account for all the mysterious flying behaviours of ballooning spiders. He first explored the idea by find out how much charge a strand must have to lift a spider of a certain weight. This turns out to range from 10 to 30 nanoCoulombs. Spider silk contains certain charge bearing amino acids and becomes negatively charged when put in contact with other materials. In theory, then, spider silk could become charge right from its release as it leaves the spinnerets, through a process known as flow electrification.

“There are thus a wide and plausible range of processes by which the strands can acquire initial charge,” Gorham writes.

As for the origin of this charge, Gorham believes the Earth itself could offer the necessary kick. The Earth has as a negative charge density of about 6 nanoCoulombs per square metre on average or more than enough give spider silk the necessary boost.  All this explains the spider’s launch power in still air, why large spiders can get such a lift and why the silk strands fan out: “because their negative charges repel.”

via Nat Geographic