The Role of Spiders in Your Garden
Our Integrated Pest Management program has long included encouraging and buying, when necessary, beneficial insects. Ladybugs, praying mantis, aphid predators and parasites, lacewings, leafminers, thrips, whitefly parasites and others offer a virtual arsenal against the specific insects the would do our garden harm. Knowing which ones to use against what problem pests is valuable knowledge for gardeners seeking to avoid harmful chemical sprays, dusts and other poisons.
There’s one beneficial insect not generally considered and, for the most part, not commercially available (except as pets) that can play an important role in keeping your garden clears of pests: the spider. Unfairly thought of as dangerous and a nuisance, especially when discovered inside your home, spiders are actually an effective predator in the garden and, despite our fears, mostly aren’t dangerous (with some exceptions).
We admit that our spider prejudice, developing since we first heard the rhyme about Little Miss Muffet, has prompted us to tear down webs and stomp on anything with eight legs that we saw. But now that’s changed.
We’ve been thinking about spiders since reading the “Attracting Pollinators and Beneficial Predators” chapter of Tammi Hartung’s The Wildlife-Friendly Vegetable Gardener. According to Hartung, spiders get a bad rap. “Spiders are amazing hunters,” she writes. “They will patrol your garden, catching and eating all manner of insect pests.”
This, of course, caught our attention. We’ve always thought of spiders as ambitious web weavers but lazy hunters. Once their web was established, they retreated to a corner and waited for some unsuspecting insect—flies, moths and whatever else was airborne in the wrong place for them but the right place for the spider—to get trapped in their net. This showed how little we knew about spiders.
Because they have eight legs—not six, as do insects—spiders are arthropods. Their group name, like the horror movie that’s reinforced their frightening reputation, is Arachnid. Spiders are generally of two kinds, the web spinners or weavers, and the hunters. Web spinners are the most visible and the ones we—okay, me—are most familiar with. But it's the hunters, those actually on the prowl and usually hard to spot, that do the most good in the garden. One of the predatory types, the wolf spider, earns its name every day.
A third type, crab spiders, lie in wait and ambush their prey.
How effective are spiders in controlling insects that might invade your garden? Studies show they are the most beneficial insect of all. They’re thought to be more efficient controlling pests than our friends the birds.
What insects do they go after? Aphids, armyworm, leafhoppers, flea-hoppers, leafminers and spider mites. They attack the spruce budworm, pine sawfly, sorghum midge and tobacco budworm. They especially like caterpillars, thrips, plant bugs, cucumber beetles, grasshoppers, scarabs and flies. Some insect pests are actually known to abandon an area once spiders move in (Hat tip to the Mecklenberg County Master Gardeners, North Carolina Cooperative Extension).
Yes, spiders are so aggressive that they’ll also capture other beneficial insects. It’s not unusual to see a bee trapped in a weaving spider’s web. But the few beneficials you’ll lose to spiders, just as you might with any predatory insect such as the praying mantis, is minimal. The harm they might do is far outweighed by the good. So don’t destroy those webs you see in the garden out of dislike for the spider.
Hartung points out another, aesthetic benefit of weaving spiders. Who doesn’t love to see an intricate, beautifully woven spider web in the sun’s first light, especially when it’s dappled with dew? This can be one of summer’s subtle but great visual joys.
Companion planting of flowers among your vegetables will help attract spiders to your garden. Weaving spiders like tall plants, sunflowers, cornstalks and the like, on which to attach their webs. Contrary to what I used to think, seeing spiderwebs hung between stalks of corn or among bean poles is a good thing. No harm is being done to the plants. Predatory spiders like mulch and ground cover. I once had a garden up against lush, shaded pasture grass. I frequently saw spiders enter my garden across the soil where the garden began, and, in the mornings, saw them retreat—they’re fast!—back to the cool protection of the grasses. If you mulch, you’ll occasionally see a predatory spider scurry back to cover when you pull back the mulch.
It’s time we got over our fear of spiders. If you see a web, don’t destroy it if you can. If you see a spider standing or racing across your garden soil, resist the urge to smash it. They’ve moved in to help themselves to the insects that might do your garden harm. That’s a good thing. Here’s a valuable page on beneficial spiders from the nonprofit gardening and education organization Edible San Marcos (Texas). These guys know their Arachnids.
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By Peter Giger
The speed and scale of the response to COVID-19 by governments, businesses and individuals seems to provide hope that we can react to the climate change crisis in a similarly decisive manner - but history tells us that humans do not react to slow-moving and distant threats.
A Game of Jenga<p>Think of it as a game of Jenga and the planet's climate system as the tower. For generations, we have been slowly removing blocks. But at some point, we will remove a pivotal block, such as the collapse of one of the major global ocean circulation systems, for example the Atlantic Meridional Overturning Circulation (AMOC), that will cause all or part of the global climate system to fall into a planetary emergency.</p><p>But worse still, it could cause runaway damage: Where the tipping points form a domino-like cascade, where breaching one triggers breaches of others, creating an unstoppable shift to a radically and swiftly changing climate.</p><p>One of the most concerning tipping points is mass methane release. Methane can be found in deep freeze storage within permafrost and at the bottom of the deepest oceans in the form of methane hydrates. But rising sea and air temperatures are beginning to thaw these stores of methane.</p><p>This would release a powerful greenhouse gas into the atmosphere, 30-times more potent than carbon dioxide as a global warming agent. This would drastically increase temperatures and rush us towards the breach of other tipping points.</p><p>This could include the acceleration of ice thaw on all three of the globe's large, land-based ice sheets – Greenland, West Antarctica and the Wilkes Basin in East Antarctica. The potential collapse of the West Antarctic ice sheet is seen as a key tipping point, as its loss could eventually <a href="https://science.sciencemag.org/content/324/5929/901" target="_blank">raise global sea levels by 3.3 meters</a> with important regional variations.</p><p>More than that, we would be on the irreversible path to full land-ice melt, causing sea levels to rise by up to 30 meters, roughly at the rate of two meters per century, or maybe faster. Just look at the raised beaches around the world, at the last high stand of global sea level, at the end of the Pleistocene period around 120,0000 years ago, to see the evidence of such a warm world, which was just 2°C warmer than the present day.</p>
Cutting Off Circulation<p>As well as devastating low-lying and coastal areas around the world, melting polar ice could set off another tipping point: a disablement to the AMOC.</p><p>This circulation system drives a northward flow of warm, salty water on the upper layers of the ocean from the tropics to the northeast Atlantic region, and a southward flow of cold water deep in the ocean.</p><p>The ocean conveyor belt has a major effect on the climate, seasonal cycles and temperature in western and northern Europe. It means the region is warmer than other areas of similar latitude.</p><p>But melting ice from the Greenland ice sheet could threaten the AMOC system. It would dilute the salty sea water in the north Atlantic, making the water lighter and less able or unable to sink. This would slow the engine that drives this ocean circulation.</p><p><a href="https://www.carbonbrief.org/atlantic-conveyor-belt-has-slowed-15-per-cent-since-mid-twentieth-century" target="_blank">Recent research</a> suggests the AMOC has already weakened by around 15% since the middle of the 20th century. If this continues, it could have a major impact on the climate of the northern hemisphere, but particularly Europe. It may even lead to the <a href="https://ore.exeter.ac.uk/repository/handle/10871/39731?show=full" target="_blank" rel="noopener noreferrer">cessation of arable farming</a> in the UK, for instance.</p><p>It may also reduce rainfall over the Amazon basin, impact the monsoon systems in Asia and, by bringing warm waters into the Southern Ocean, further destabilize ice in Antarctica and accelerate global sea level rise.</p>
The Atlantic Meridional Overturning Circulation has a major effect on the climate. Praetorius (2018)
Is it Time to Declare a Climate Emergency?<p>At what stage, and at what rise in global temperatures, will these tipping points be reached? No one is entirely sure. It may take centuries, millennia or it could be imminent.</p><p>But as COVID-19 taught us, we need to prepare for the expected. We were aware of the risk of a pandemic. We also knew that we were not sufficiently prepared. But we didn't act in a meaningful manner. Thankfully, we have been able to fast-track the production of vaccines to combat COVID-19. But there is no vaccine for climate change once we have passed these tipping points.</p><p><a href="https://www.weforum.org/reports/the-global-risks-report-2021" target="_blank">We need to act now on our climate</a>. Act like these tipping points are imminent. And stop thinking of climate change as a slow-moving, long-term threat that enables us to kick the problem down the road and let future generations deal with it. We must take immediate action to reduce global warming and fulfill our commitments to the <a href="https://www.ipcc.ch/sr15/" target="_blank" rel="noopener noreferrer">Paris Agreement</a>, and build resilience with these tipping points in mind.</p><p>We need to plan now to mitigate greenhouse gas emissions, but we also need to plan for the impacts, such as the ability to feed everyone on the planet, develop plans to manage flood risk, as well as manage the social and geopolitical impacts of human migrations that will be a consequence of fight or flight decisions.</p><p>Breaching these tipping points would be cataclysmic and potentially far more devastating than COVID-19. Some may not enjoy hearing these messages, or consider them to be in the realm of science fiction. But if it injects a sense of urgency to make us respond to climate change like we have done to the pandemic, then we must talk more about what has happened before and will happen again.</p><p>Otherwise we will continue playing Jenga with our planet. And ultimately, there will only be one loser – us.</p>
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