Sunday, March 19, 2017

Spiders are your friend, if you don't like all the other creepy-crawlies

So if you live in the Islands, you’ve got geckos in your house, and they’re annoying. But just how many insects are they removing to survive?

Probably a lot—and that’s a good thing for both your sanity and your health.

It turns out the spiders around your home, similarly annoying, are also removing insects from the environment—a lot of insects.

(Image: You won't find this one around your home. It's a sea spider, photographed by teacher Kaitlin Baird from a NOAA bottom trawl. Sea spiders are deep water creatures that tend to have very long legs and tiny bodies. Credit: Kaitlin Baird/NOAA.)

Globally, spiders are taking out 400 to 800 million tons of insects. A stunning amount.

That’s from calculations done by the authors of this paper

(Okay, we ought here to clarify that spiders are not themselves insects. Spiders are arachnids, and they have two main body parts and eight legs. Insects are six-legged creatures with three main body parts. There are other differences as well, but that should suffice for this discussion.)

Spiders have a much bigger impact in natural environments than disturbed or urban environments, but, still. They account for a lot of pest control.

One of the findings of the paper above is that if you remove spiders from the environment, you can expect a big rebound in insect populations.

“Our estimates are supported by the published results of exclusion experiments, showing that the number of herbivorous/detritivorous insects and collembolans increased significantly after spider removal from experimental plots.”

(Yeah, collembolans. Six-legged critters that used to be considered insects but no longer are. Commonly called springtails, for their prodigious jumping capacity.)

You may worry about predators like sharks and bears and snakes and mosquitoes, but spiders, say authors Martin Nyffeler and Klaus Birkhofer, are “the most common and abundant predators in terrestrial ecosystems.”

The Eurekalert press release on their study is here. 

If you have spiders in your garden, think twice before removing them. All spiders are carnivores—they eat other creepy-crawlies and only very rarely will one munch a plant.

Hawaii has lots of introduced spiders, but its native spiders are a fascinating bunch. The happy-faced spider is perhaps the most famous, but there are lots more. The Nature Conservancy’s Sam Gon writes about some of them here

If you’re interested in the tiny critters of the island, I can recommend “What’s Bugging Me,” by Gordon M. Nishida and Joann M. Tenorio. And "What Bit Me?" by the same pair.

© Jan TenBruggencate 2017


Eric said...

Fleas, ticks, and mites aren't collembolans – perhaps you were thinking of springtails?

Jan T said...

Thanks Eric, made the correction. This is not an area I know a lot about, and I had found a bad source that suggested those suckers were collembolans--perhaps because of the jumping abilities of the fleas.

Lorna said...

I know crab spiders eat insects, but what I've found in my yard is that they trap a lot of honeybees. I get rid of the crab spiders, and leave the garden (black/yellow) spiders alone. Should I leave the crab spiders alone, too?