An Orb-weaver spider (Araneus diadematus) in Rennes, western France (Photo: Damien Meyer/ AFP/Getty Images)
Show Hide image

City living is making spiders bigger, study finds

According to new research, city-dwelling spiders are larger and more fertile than their rural-dwelling relatives.

The growth of cities destroys the homes of many animals. With habitats drenched in cement, their only option is to relocate - and in the worst cases, urban expansion can cause species extinction. However, it’s not all doom and gloom for some species, as city living appears to bring out the best in them. Have you noticed that spiders are looking meatier nowadays?

According to new research, city-dwelling spiders are flourishing. Similar to rats and pigeons, spiders are “urban exploiters”. This means that they thrive in urban surroundings. Despite our squeamish attitudes towards them, spiders are important creatures: they greatly impact food webs, plant colonies and herbivore abundance, and they help to control the insect populace.

Most research on the expansion of cities focuses on birds. For instance, noise pollution has forced birds to change their calls, while other studies show that some birds have even stopped migrating. Researchers from the University of Sydney, however, were interested in the changes in spider anatomy that might have come from living in cities, and specifically Golden Orb-Weaving (Nephilla Plumipes) spiders, which are common in both urbanised and rural Australian landscapes. They build strong semi-permanent webs with golden-looking silk, and, once matured, they reside in this web their entire life. Thus, their “coach potato” lifestyle makes them ideal research subjects.

The researchers collected 222 spiders from rural and urbanised areas. All spiders were female and had reached maturity, and their body size, fat reserves, and ovary weight were recorded. The findings showed that rural-dwelling spiders had smaller bodies, but that city-dwelling spiders were larger, and more fertile. Places with roads, buildings and a lack of greenery typically denoted larger spiders. The researchers proposed that temperature differences could explain these results, as cities are much warmer than rural areas thanks to the urban heat island effect.

Their results could also reflect differences in prey availability. The study's lead author, ecologist Elizabeth Lowe, explained in more detail:

There were strong associations in particular between spider size and the presence of hard surfaces (such as roads and buildings) and lack of vegetation. These hard surfaces contribute to the urban “heat island” effect, which makes it warmer in cities than surrounding areas. It is also likely that there is more food for the spiders in the city as a result of night lighting and increased resources. This combination of warm temperatures and more food would allow spiders to put more energy towards growth and reproduction. Fewer predators and parasites in urban areas could also allow urban spiders to grow larger.”

This study is only applicable to one species of spider in one Australian city, so it's not fair yet to say that all urban spiders are getting bigger - so don't panic about huge spiders with larger ovaries just yet. However, the researchers pledge that this is promising news:

The fact that some spiders benefit from urbanisation is a good thing. In order to maintain biodiversity in cities, we need to be able to support diverse populations of spiders and other invertebrates” Lowe said. “By gaining a better understanding of the impacts of urbanisation on wildlife in cities, we can work towards creating healthy, functioning ecosystems in urban areas." 

AKG-IMAGES
Show Hide image

High explosive, damp squibs: the history of bombing raids

Governing from the Skies by Thomas Hippler examines the changing role of aerial bombing.

Bombing from the air is about a hundred years old. As a strategic option, it eroded the distinction between combatants and non-combatants: it was, Thomas Hippler argues in his thought-provoking history of the bombing century, the quintessential weapon of total war. Civilian populations supported war efforts in myriad ways, and so, total-war theorists argued, they were a legitimate object of attack. Bombing might bring about the collapse of the enemy’s war economy, or create a sociopolitical crisis so severe that the bombed government would give up. Despite efforts to protect non-combatants under international law, civilian immunity has been and continues to be little more than an ideal.

Hippler is less concerned with the military side of bombing, and has little to say about the development of air technology, which, some would insist, has defined the nature and limits of bombing. His concern is with the political dividends that bombing was supposed to yield by undermining social cohesion and/or the general willingness to continue a war.

The model for this political conception of bombing was the colonial air policing practised principally by the British between the world wars. Hippler observes that the willingness to use air power to compel rebel “tribesmen” in Afghanistan, Iraq and Africa to cease insurgency became the paradigm for later large-scale campaigns during the Second World War, and has been reinvented in the age of asymmetric warfare against non-state insurgencies: once again in Iraq and Afghanistan – and, indeed, anywhere that a drone can reach.

The problem, as Hippler knows, is that this type of bombing does not work. A century of trying to find the right aerial platform and armament, from the German Gotha bombers of 1917 to the unmanned missile carriers of today, has not delivered the political and strategic promise that air-power theorists hoped for. Air power is at its best when it is either acting as an ancillary to surface forces or engaged in air-to-air combat. The Israeli strike against Arab air forces at the start of the 1967 war was a classic example of the efficient military use of air power. In the Second World War, the millions of bombs dropped on Europe produced no social upheaval, but the US ­decision to engage in all-out aerial counterattack in 1944 destroyed the Luftwaffe and opened the way to the destruction of Germany’s large and powerful ground forces.

The prophet of bombing as the means to a quick, decisive solution in modern war was the Italian strategist Giulio Douhet, whose intellectual biography Hippler has written. Douhet’s treatise The Command of the Air (1921) is often cited as the founding text of modern air power. He believed that a more humane way to wage war was to use overwhelming strength in the air to eliminate the enemy’s air force, and then drop bombs and chemical weapons in a devastating attack on enemy cities. The result would be immediate capitulation, avoiding another meat-grinder such as the First World War. The modern nation, he argued, was at its most fragile in the teeming industrial cities; social cohesion would collapse following a bombing campaign and any government, if it survived, would have to sue for peace.

It has to be said that these views were hardly original to Douhet. British airmen had formed similar views of aerial power’s potential in 1917-18, and although the generation that commanded the British bomber offensive of 1940-45 knew very little of his thinking, they tried to put into practice what could be described as a Douhetian strategy. But Douhet and the British strategists were wrong. Achieving rapid command of the air was extremely difficult, as the Battle of Britain showed. Bombing did not create the conditions for social collapse and political capitulation (despite colossal human losses and widespread urban destruction) either in Britain, Germany and Japan, or later in Korea and Vietnam. If Douhet’s theory were to work at all, it would be under conditions of a sudden nuclear exchange.

Hippler is on surer ground with the continuity in colonial and post-colonial low-­intensity conflicts. Modern asymmetric warfare, usually against non-state opponents, bears little relation to the total-war school of thinking, but it is, as Hippler stresses, the new strategy of choice in conflicts. Here too, evidently, there are limits to the bombing thesis. For all the air effort put into the conflict against Isis in Syria and Iraq, it is the slow advance on the ground that has proved all-important.

The most extraordinary paradox at the heart of Hippler’s analysis is the way that most bombing has been carried out by Britain and the United States, two countries that have long claimed the moral high ground. It might be expected that these states would have respected civilian immunity more than others, yet in the Second World War alone they killed roughly 900,000 civilians from the air.

The moral relativism of democratic states over the century is compounded of claims to military necessity, an emphasis on technological innovation and demonisation of the enemy. For all the anxieties being aired about militant Islam, the new Russian nationalism and the potential power of China, it is the United States and Britain that need to be watched most closely.

Richard Overy’s books include “The Bombing War: Europe (1939-1945)” (Penguin)

This article first appeared in the 16 February 2017 issue of the New Statesman, The New Times