Global spider community eats 4-800 MN tons of insects annually

In a study published in the online journal Science of Nature on March 14, researchers set out to put a value on the ecological importance of arachnids, reports the BBC.

There are over 45,000 species of arachnids in the world today, covering every size imaginable and sometimes having a population density ranging up to 1,000 individuals per square meter (10,764 square feet). Suffice to say that spiders are the most species-rich and widest-ranging groups of predators in the world.

Two of the 10 trapdoor spider species found in Queensland.

Jeremy Wilson/University of Queensland

Dr. Martin Nyffeler, the University of Basel scientist who led this study, became interested in the ecological importance of spiders after reading a 1958 book called The World of Spiders. The author, William Bristowe, piqued Nyffeler’s curiosity after suggesting the total weight of insects killed each year by the British spider population exceeded that of the human population in Britain.

Dr. Nyffeler spent hundreds of hours studying spider behavior in the field as well as gathering studies on spider ecology published around the world.

“These 40 years of gathering experience – spending thousands of hours dealing with spider prey capture rates and prey selection – was needed to be able to write this paper on the global annual prey kill of the spiders,” he said in an email to the BBC.

Orchesella cincta, a common springtail. Photo taken in Ghent, Belgium.

Mvuijlst/Wikimedia

Using a number of models, the researchers were able to show that globally, the spider population was able to wipe out 20 times their weight in insects every year. Over 90 percent of the prey are insects and springtails (Collembola), while some big, tropical spiders will dine on plants, invertebrates and small fish and frogs occasionally.

The researchers determined that the total weight of arachnid population worldwide is about 25 million tons, while they consume 400 to 800 million tons of insects annually. Now, that is a lot of insects. The study is not meant to frighten anyone, but instead, it should make us more aware of the role spiders play in the global food web.

Aphonopelmas (anax or hentzi) from Independence Creek, SW Texas

Dallas Krentzel

“Spiders kill large numbers of herbivorous insects – and by doing so they help to protect the plants from herbivore damage,” said Dr. Nyffeler.

“They serve as food for thousands of arthropod-eating animals – an estimated 8,000-10,000 specialized insect species and many passerine birds (an estimated 3,000-5,000 species) feed on spiders.”