Bloodlust spiders surpassed the appetites of mankind
The biomass of victims that spiders eat in a year, is variously estimated from 400 to 800 million tons.
European zoologists was convinced that spiders are one of the most dangerous predators on Earth. The biomass of victims that spiders eat in a year, is variously estimated from 400 to 800 million tons. This is about one-hundredth of the entire net primary production of the planet. The article was published in The Science of Nature.
Spiders appeared in the Devonian period of the Paleozoic era and are now one of the most widespread predators on the planet.
Per square meter of sushi has, on average, about 130-150 spiders.
In good conditions this number increases to 1,000 individuals. Describes more than forty five thousand species of spiders; they have widely different behaviors and adapt to various environmental conditions.
Spider-lynx
There are spiders that hunt other spiders and even birds, fish and frogs, but the bulk of them are predators, eating insects and springtails. Spiders are able to survive in the most extreme conditions, to fly from place to place, like balloons on a string-web, and to occupy almost any site.
Some spiders of the family of linyphiid travel around 30 kilometers per day, while in Norway these spiders walking on snow at temperatures up to -7 degrees Celsius. Spiders are in the hottest deserts, on the northernmost Islands, in the deepest caves and the highest mountains. Hardly on Earth is a piece of land, where the spiders would be completely lacking, the researchers note.
Mostly spiders hunt in the forests and meadows. Farmlands they kill far fewer victims. This is likely due to the influence of man and a small number of spiders themselves. According to previous research, when removing spiders from the ecosystem, the number of herbivores and detritophagous insects and springtails in it increases significantly.
However, to estimate exactly how much spiders eat, is difficult, because many of them have a rather secretive way of life, and hunted, for example at night, or hiding among the forest litter.
In a new paper, the researchers distributed taken from 65 studies, the average biomass themselves of spiders per square meter in seven types of habitats: tropical forests, temperate and cold temperate forests, tropical grasslands and savannas, moderate grasslands and Mediterranean shrubs, annual of arable land, deserts and Arctic tundra. Then they extrapolated the obtained average figures for the real area of these places and got the overall figures for the biomass of spiders living in them.
Next, using the two different methods was assessed the average biomass of the victims that spiders eat in a year in each of the habitat types. The first method took into account the needs of spider food per unit of body weight; the second method used data for the hunting spiders, including the spider, the number of victims in the field observations and the density of the arachnoid veil.
While trapped in the web, but not eaten prey is also considered a victim because she usually died.
This is particularly important to consider the food preferences of some species, such as large spiders of the family of Orb-web spiders, which often kill their victims just.
It turned out that most spider victims — about three hundred million tons, which accounts for tropical forests.
Overall, according to the applied assessments, spiders kill from 400 to 800 million tons of victims per year, over ninety percent of which occur in insects and springtails.
For comparison it should be noted that, for example, all cetaceans per year eat from 280 to 500 million tons, and humanity as a whole for the year uses 400 million tons of meat and fish (according to the Food and agriculture organization of the UN). Although some spiders sometimes eat plants, scientists were able to numerically confirm that these arthropods are among the most fearsome predators on Earth.
Anna Canazei