Underappreciated but Ecologically Important, Spiders are Declining

According to a team of researchers at King Juan Carlos University (URJC) in Spain, it isn’t just cute and cuddly species that are being threatened by human activity and deserve protections to save them from extinction.  Spiders are also declining in habitats around the world—and though some people might be tempted to let them disappear, the truth is these arachnids serve important environmental and economic functions.  More broadly, the decline of spiders suggests groups of animals that have not been as closely studied as closely as mammals, birds, and reptiles are just as vulnerable to extinction as other species.

Scientists in the URJC Biodiversity and Conservation Department were prompted to study spider extinction when they noticed the arachnids seem under-represented on the International Union for Conservation of Nature’s “Red List” of threatened and endangered species.  The Red List is used by scientists and environmentalists to keep track of the conservation status of plants and animals, and lists species that have been studied and deemed to be “critically endangered,” “endangered” or “vulnerable.”

The great bulk of species on the Red List are vertebrates (animals with a backbone like birds, mammals, reptiles, and fish) and plants.  The absence of many spider species is particularly noticeable, so URJC researchers decided to study whether spider populations might somehow be more resistant than other species to the impacts of human activity.  Unfortunately for the eight-legged invertebrates, it turns out spiders have no special resistance to extinction.  More likely, their absence on the Red List is simply due to the fact that spider conservation hasn’t been a high priority, so the endangered status of most species has not been formally determined.

In the course of their research, the URJC team examined 173 scientific papers that look at the health of spider populations, all of them published since the year 1980.  “The technique used meant we could rigorously combine the results of a lot of studies,” say Samuel Prieto-Benítez and Marcos Méndez of URJC.  “This is regularly used in medicine in order to arrive at general conclusions about the effects of drugs, based on numerous trials with more limited coverage.”

The research team concluded that in fact spiders are rapidly declining, largely due to the impacts of human agriculture.  Agricultural practices like clearing forests and other native ecosystems, plowing the soil, and grazing livestock all destroy spider habitat—as well as that of countless other invertebrates.  Widespread use of pesticides in agriculture also hurts spider populations.  This is pushing many species toward extinction, with serious consequences for people.

Spiders may not be cute, but they play an important role in most land-based ecosystems.  Spiders are predators that help keep the populations of pest insects in check, and fewer spiders in the world will mean more insects that feed on crops and cause economic damage to the farming industry.  By killing off spiders and other predators, pesticides could actually have a counter-productive impact and lead to more agricultural pests.

Fortunately the URJC study also points to some ways to minimize the damage to spider populations.  For example organic agriculture, which avoids the use of pesticides and often involves less extreme alterations in the landscape, has fewer negative effects on spiders than traditional industrialized farming.  Organic agriculture of course has numerous other benefits as well, such minimizing reliance on fossil fuels and on synthetic compounds that could harm human health.    

Declining spider populations are a reminder that invertebrates and other less-flashy animal species are just as vulnerable to extinction as larger and better-known birds and mammals.  The importance of spiders in natural ecosystems also underlines the fact that even the most unpopular animals can be ecologically and economically very significant.  Spiders might not be cute or cuddly, but they have an essential role to fill in the planet’s natural systems, and protecting them is just as important as preserving larger and more charismatic creatures. 

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