Curious Kids: why do spiders need so many eyes but we only need two?



Jumping spiders, like this one, usually have eight eyes: two very large front eyes to get a clear, colour image and judge distance, and extra side eyes to detect when something is moving.
Flickr/Thomas Shahan, CC BY-NC-ND

Samantha Nixon, The University of Queensland and Andrew Walker, The University of Queensland

Curious Kids is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.


Can you find out why spiders need six eyes but we only need two? – Amos, age 3, Newcastle.


Hi, Amos. Thanks for your excellent question.

The first thing we should say is that while it’s true that some spiders have six eyes, most actually have eight.

The short answer to your question is that animals have evolved different eyes that best suit the lives they lead.




Read more:
Curious Kids: What are spider webs made from and how strong are they?


Humans have two eyes that face forward. Our eyes are very good at seeing colours and shapes. Having two big eyes in the front of our head means they can work together to guess how far away something is (we call this “judging distance”). That makes it easier for us to catch another animal so we can eat it.

Spiders are also hunters and they need eyes that help them find and catch their food. In fact, most spiders can’t see very well, and use touch and taste to explore the world. But the kind of eyes they have tells us something about the food they eat and the lives they live.

Spider eyes for spider lives

Jumping spiders are active hunters, like tiny lions chasing down their prey (bugs). They usually have eight eyes: two very large front eyes to get a clear, colour image and judge distance, and extra side eyes to detect when something is moving. Here’s a picture of an Australian jumping spider.

Jumping spiders need two big eyes on the front so they can guess how far away their prey is.
Michael Duncan., Author provided

Some spiders make nets to catch their prey. These net-casting spiders also need to see clearly and judge distances. Some have developed huge, scary-looking black eyes that stare straight ahead, so they are nicknamed ogre spiders! These gigantic eyes help the spider to see a wide area and accurately throw down its spider web net to catch its prey. Here’s a picture of a net-casting spider.

This net-casting spider is from the Deinopis family. The little dots that look like nostrils are actually eyes!
Michael Duncan, Author provided

Some spiders live in caves that are completely dark, where eyes are no use at all. They have to rely on other senses to find their food in the dark. To save energy making eyes, these spiders lost their eyes during evolution, so now some of them have no eyes at all. You can see a picture of a spider like that here.

So why did most spiders end up with so many eyes?

Both human and spider eyes are the result of slowly evolving to help us survive in our different environments. One reason our human eyes are different from spiders is because our bodies and brains are also built differently.

For example, spiders don’t have necks. So they can’t turn their heads to look at things like we can. Having extra eyes around their heads is one way that spiders see more of the world around them, helping them to quickly spot prey or a potential predator.

Human eyes and spider eyes also do different jobs. Our two eyes are very complex and are good at doing many jobs at once, while spiders have different sorts of eyes that do different jobs.

For example, the large central eyes of jumping spiders are best for seeing shapes, but the simple side eyes have the important job of watching out for predators.

So a two-eyed spider or even an eight-eyed human isn’t impossible. But the two eyes we have and the eight eyes most spiders have are perfectly suited to help each of us live our lives just the way they are.




Read more:
Curious Kids: why do spiders have hairy legs?


Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au


CC BY-ND

Please tell us your name, age and which city you live in. We won’t be able to answer every question but we will do our best.The Conversation

Samantha Nixon, PhD, The University of Queensland and Andrew Walker, Postdoctoral Research Fellow, The University of Queensland

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

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Climate change is killing off Earth’s little creatures



File 20190116 152983 bx2j9j.jpg?ixlib=rb 1.1
A jumping spider, which uses sharp eyesight to hunt its prey.
ThomasShahan.com/Flickr, CC BY-SA

Bill Laurance, James Cook University

Climate change gets blamed for a lot of things these days: inundating small islands, fueling catastrophic fires, amping-up hurricanes and smashing Arctic sea ice.

But a global review of insect research has found another casualty: 40% of insect species are declining and a third are endangered. It confirms what many have been suspecting: in Australia and around the world, arthropods – which include insects, spiders, centipedes and the like — appear to be in trouble.




Read more:
Curious Kids: why do spiders have hairy legs?


The global review comes hard on the heels of research published in the Proceedings of the National Academy of Sciences USA that suggests a potent link between intensifying heat waves and stunning declines in the abundance of arthropods.

If that study’s findings are broadly valid – something still far from certain – it has chilling implications for global biodiversity.

Our natural world depends on arthropods.
Steve Raubenstine/Pixabay

Arthropod Armageddon

In the mid-1970s, researchers on the Caribbean island of Puerto Rico conducted a large-scale study to measure the total biomass (living mass) of insects and other arthropods in the island’s intact rainforests, using sweep nets and sticky-traps.

Four decades later, another research team returned to the island and repeated the study using identical methods and the same locations. To their surprise, they found that arthropod biomass was just one-eighth to one-sixtieth of that in the 1970s – a shocking collapse overall.

And the carnage didn’t end there. The team found that a bevy of arthropod-eating lizards, birds and frogs had fallen sharply in abundance as well.

Insects are crucial in food webs for species such as this hummingbird.
Pixabay

In the minds of many ecologists, a widespread collapse of arthropods could be downright apocalyptic. Arthropods pollinate some of our most important food crops and thousands of wild plant species, disperse seeds, recycle nutrients and form key links in food chains that sustain entire webs of life.

This ecological ubiquity arises because arthropods are so abundant and diverse, comprising at least two-thirds of all known species on Earth. In the 1940s, evolutionary biologist J. B. S. Haldane quipped that “God has an inordinate fondness for beetles.” Humans might think we rule the world, but the planet really belongs to arthropods.

Killer heat waves

The researchers who documented the arthropod collapse in Puerto Rico considered a variety of possible causes, including pesticides and habitat disruption. But the evidence kept pointing to another driver: rising temperatures.

Weather stations in Puerto Rico indicate that temperatures there have risen progressively in the past several decades – by 2℃ on average.

But the researchers are far less worried about a gradual increase in temperature than the intensification of heat waves—which have risen markedly in Puerto Rico. This is because nearly all living species have thresholds of temperature tolerance.

For example, research in Australia has shown that at 41℃, flying foxes become badly heat-stressed, struggling to find shade and flapping their wings desperately to stay cool.

But nudge the thermometer up just one more degree, to 42℃, and the bats suddenly die.

In November, heat waves that peaked above 42℃ in north Queensland killed off almost a third of the region’s Spectacled Flying Foxes. The ground beneath bat colonies was littered with tens of thousands of dead animals. Dedicated animal carers could only save a small fraction of the dying bats.

Bats die en-masse during a recent heatwave.

The El Niño connection

El Niño events – fluctuations in Pacific sea-surface temperatures that drive multi-year variations in weather across large swaths of the planet – are also part of this story. New research appears to be resolving longstanding uncertainties about El Niños and global warming.

Recent studies published in Nature and Geophysical Research Letters suggest global warming will in fact intensify El Niños – causing affected areas to suffer even more intensively from droughts and heat waves.

And this ties back to Puerto Rico, because the researchers there believe a series of unusually intense El Niño heatwaves were the cause the arthropod Armageddon. If they’re right then global warming was the gun, but El Niño pulled the trigger.

Beyond heat waves

Puerto Rico is certainly not the only place on Earth that has suffered severe declines in arthropods. Robust studies in Europe, North America, Australia and other locales have revealed big arthropod declines as well.

And while climatic factors have contributed to some of these declines, it’s clear that many other environmental changes, such as habitat disruption, pesticides, introduced pathogens and light pollution, are also taking heavy tolls.

Monarch butterflies are declining in the USA and Mexico, probably from habitat disruption.
Pixabay

So, at a planetary scale, arthropods are suffering from a wide variety of environmental insults. There’s no single reason why their populations are collapsing.




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Climate change: effect on sperm could hold key to species extinction


The bottom line is: we’re changing our world in many different ways at once. And the myriad little creatures that play so many critical roles in the fabric of life are struggling to survive the onslaught.The Conversation

Bill Laurance, Distinguished Research Professor and Australian Laureate, James Cook University

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

The truth about spider bites in Australia – they’re unlikely to eat your flesh


Ronelle Welton, University of Melbourne and Bill Nimorakiotakis, Epworth Hospital

Recent news reports that a man had both his legs amputated after being bitten by a white-tailed spider have again cast this relatively harmless spider in a negative light. Experts have since said amputations may have been wrongly blamed on a spider bite, and authorities now consider a bacterial infection to be responsible for the man’s injuries. Despite this, the damage to the largely harmless white-tail may have been done. The Conversation

The venom from the white-tailed spider is listed as non-lethal.
It has not been shown to cause necrotic ulcers, which could result in the need for amputation. And there has never been any clear evidence necrotising arachnidism – the name give to a syndrome where the skin blisters and ulcerates following spider bites – has been seen in Australia.

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There is currently no clinical test to determine if you have been bitten by a spider. And there is no blood or swab test that can be performed to positively identify what spider it is if a bite is suspected. Whether it is a bite from a spider or another insect, the management is the same – most will get better without any medical treatment.

Spiders in Australia

The majority of spiders in Australia are voracious predators of insects. For the most part, they play a useful role in lowering insect numbers.

The venom transmitted through bites of some Australian spiders can cause harm to humans and even be life-threatening. The better known of these are the redback spider (Latrodectus hasselti), and the funnel-web spiders (genera Atrax and Hadronyche). Antivenom is available for both spiders.

Redback spider venom can cause a lot of pain. Advice would be to go to hospital if pain lasts for longer than a few hours and simple pain relief is not helping. Funnel-web spider venom can cause local swelling in addition to increasing heartbeat, salivation, muscle spasms and respiratory distress (trouble breathing).

Without appropriate first aid, quick access to hospital and antivenom, these bites can be lethal. For the “big black hairy” funnel-webs, appropriate first aid needs to be applied and it is advisable to call 000.

The redback spider is considered one of the most venomous to humans in Australia.
graibeard/Flickr, CC BY

Other spiders that have concerning bites include the trapdoor, whistling, sac, ground, orb and huntsman spiders. These may cause milder symptoms such as headache, swelling and pain, which does not last for a long time.

The white-tailed spider

White-tailed spiders (Lampona sp.) can be recognised by their cylindrical body shape and a white or grey spot on the end of their abdomen. They are found in eastern and most southern areas of Australia and New Zealand.

These spiders are active hunters, preying on other types of spiders and insects. They may transiently roam inside houses, especially in warmer weather, where they may be found in bedding or clothing that has been left on the floor.

One study of over 70 spider bite cases in which white-tailed spiders were identified showed patients experienced only a mild localised reaction, such as swelling, local pain or headache. To date clinical research has not been able to associate tissue loss with the venom of these spider bites.

Flesh-eating bacteria

The man at the centre of the recent story linking amputations to a white-tail spider bite was said to have a “flesh eating” infection. But there is a very low probability of an association between spiders and necrotisisng fasciitis (commonly known as flesh-eating disease).

Of course, any injury that causes a break in our skin leaves the capacity for bacteria to enter our body. Therefore be sure to keep an injury area clean. Questions have been raised as to the possibility of a spider introducing infections, but again, despite it being theoretically possible, it is unlikely.

Contributing factors to infection are if people have conditions such as diabetes or take medications, such as steroids like prednisolone, that lessen the body’s ability to fight infection.

How to prevent spider bite

  • Leave them alone
  • wear gloves if gardening
  • humanely remove spiders from your home and limit hiding spaces where possible inside the home
  • knock out shoes before putting them on; these are nice quiet homes for spiders.

For first aid after a spider bite, please see the Australian guidelines. Many bites don’t result in envenoming and death is very rare, so it is important to remain calm. But seek medical attention if there are concerning symptoms such as those described above: difficulty breathing, increased heartbeat and pain lasting longer than an hour.

Ronelle Welton, Scientist AVRU, University of Melbourne and Bill Nimorakiotakis, Associate Professor, Epworth Hospital

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

Spiders are a treasure trove of scientific wonder


Maggie Hardy, The University of Queensland

Australia has an incredible diversity of native spiders, including the potentially lethal funnel-web, the ubiquitous huntsman, and the charming peacock spider. Only two can be deadly for humans – the funnel-web and redback spiders – and we have antivenom for both.

Found all across the country, spiders play an important role in the environment as generalist predators. Increasingly, their venom is being used to develop novel human therapeutics and to create new, selective, sustainable insecticides.

A model citizen

How house spider webs change when the spider is exposed to different chemicals.

Spiders are often a starting point for children to fall in love with the natural world: they’re found almost everywhere, and everyone can appreciate their tremendous diversity. What’s more, scientists are constantly learning new things from them.

They’re an important model system to help us understand the basics of biology. We know that the spider and its web are so closely tied that exposure to different chemicals has specific effects on how the webs are spun.

Other research suggests the blue colour in tarantulas evolved independently at least eight times. This may help inform our understanding of the evolution of colouration, as well as how to make better paints.

The peacock spider has helped show that strong sexual selection by females depends on a variety of factors. Scientists think sexual selection has had an impact on the striking coloration and complex signalling of this spider species, but this is the first evidence to definitively demonstrate female preference has played a role.

Dance, dance revolution

With great power…

As a generalist predator, spiders help limit the number of insects in your garden. Although they’ll probably eat some good bugs as well as bad while they’re at it.

Spider venom is a complex chemical cocktail of hundreds of different components, and each type has its own very specific activity. Many individual venom components act on the insect nervous system and these can be very useful for scientific research.

My work, for instance, is on discovering newenvironmentally friendly insecticides from spider venoms. Since insect nervous systems are very different from the one found in vertebrates (including humans), individual toxins are frequently active in insects but not in vertebrates, and vice versa.

The Chemistry of Spider Venom
Compound Interest, CC BY-NC-ND

When we look for good insecticidal candidates we screen for compounds with specific activity in insects and the absence of activity in vertebrates. It’s that specificity that makes spider venoms such powerful sources of new, sustainable insecticides, as well as excellent therapeutics.

What’s in a venom?

Spider venoms generally consist of three types of components: small components (salts, carbohydrates, amines and acids to name a few); peptides (small proteins that are generally highly structured); and enzymes (used for digesting food).

If you get bitten by a spider, do your best to remain calm, and proceed directly to a medical professional so your symptoms can be monitored and treated. They will administer the appropriate antivenom if required.


The Conversation

Spiders deliver venom by injection, using mouth parts called chelicerae, which are informally known as fangs. The chelicerae are found on the front body segment, the cephalothorax, and that’s also where its eight legs are attached.

The abdomen is the other spider body segment, and that’s where the spinnerets, used to weave the web, are found.

Spiders sometimes appear hairy, but those are actually sensory setae that are used to collect detailed information about the nearby environment. Depending on the spider species that could include temperature, humidity, and wind direction, and chemical information, such as the source of pheromones used in mating.

So leave your fear behind and go ahead, embrace the majesty of spiders. But pick your species carefully – and try not to get the police involved.

This article is part of our series Deadly Australia. Stay tuned for more pieces on the topic in the coming days.

The Conversation

Maggie Hardy, Postdoctoral Research Fellow, The University of Queensland

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