No, the spiders will not eat all the people
I talked about this a little in my original For the Love of Spiders post, but researchers have just published an article about exactly how much spiders eat. It’s a lot. In a paper in the Science of Nature researchers Martin Nyffeler and Klaus Birkhofer estimated how they eat and, thereby, how big a role they really play in our ecosystems. In their estimate, spiders eat 400–800 million metric tons of prey each year! As the Washington Post put it, that is more than the weight of all humans on the planet. One, that’s a lot of prey. And two, that’s a lot of spiders! (Also, no spiders could and would not eat all people, it’s just a comparison of weights.)
There are more than 45,000 species of spider that have been described and many many more that have not been described (as is generally true for all insects). Spider density and, therefore, prey consumption are greatest in forests and grasslands. Spiders, however, only play a minor role in agricultural systems. The authors speculate that this is because agricultural fields are disturbed, meaning mostly that large plants are not able establish. But, seriously, there are still so many spider in my garden and most of the production fields I’ve been in. There are so many of them, and they are so cool!
What are their prey? And what would those prey animals be doing if they weren’t eaten by spiders?? According the literature review conducted in the paper, the top groups eaten by spiders are Diptera (flies), Hemiptera (true bugs like assassin bugs), Hymenoptera (wasps, bees, and ants), Collembola (very old insects), Coleoptera (beeltes), Lepidoptera (moths and butterflies), Orthoptera (crickets), and Araneae (spiders).
If these weren’t eaten by spiders, they could be doing things like buzzing around your head at a picnic and eating decomposing leaves. Although population growth followed by starvation would probably kill many of them even without predators.
I am going to take advantage of this occasion to put up all my pictures of spiders and spiders eating stuff that I have posted yet. I don’t have as many as I should really, but I like them anyway. I am going to go in order of frequency of prey. Flies are very common so it makes sense that they are a main prey item. Here is a picture of a spider eating a hover fly in my garden.
Hemiptera, the true bugs to an entomologist, include sedentary insects like aphids, which make easy prey for hunting spiders. I’ve never actually captured that on camera or video, but I’ve seen it happening. Bees and wasps are also very common and often visit flowers for nectar. A flower is a good place to be grabbed by a spider, as is happening in the picture below.https://getbuggy.wordpress.com/2016/02/08/for-the-love-of-spiders/.
I don’t have pictures of spider predation of Collembola, Coleoptera, Lepidoptera, or Orthoptera. I’m actually pretty surprised that I don’t a have photo of spiders eating moths since moths are often caught in webs. Here is a spider of a web though. Orbs spiders, like the one pictured below, are common web predators in gardens and forest. Despite the fact that they look scary, they are harmless.
That’s all I’ve got for now. Don’t let the spiders eat you!