Along Came a Spider

Photo © M. Fazian

By Lauren Flesher

They’re stealthy. They’re quick. They have far too many legs. They’re spiders, and they’ve been vilified for centuries. They’re not all bad, though. Spiders perform a great many ecosystem services, from agricultural pest control to disease prevention. They’re especially beneficial to native birds. Here are some key reasons a true bird lover should leave that spider alone.

A Flycatcher With A Fly-catcher
A Flycatcher With A Fly-catcher

This Eastern Phoebe has snagged a delicious spider snack.

Spiders as Bird Food

Spiders are like an energy bar for birds—the bite-sized packs of protein are incredibly nutritious. This is especially important during migration, when birds are physically taxed and need much more food to keep going. Many species of smaller birds, particularly hummingbirds, will also take advantage of a sticky spider web and steal the captured insects from the silk. It’s the bird equivalent of a convenience meal!

Nests That Stretch
Nests That Stretch

This Anna's Hummingbird nest incorporates spider webs, allowing the nest to accommodate growing chicks.

Spiderwebs and Nests

Many species of birds use spider silk when constructing their nests. It has the advantage of being strong while also being flexible. As the nestlings grow, the nest can stretch with them, and the silk allows for easy repair in the case of damage.

Spider Eggs Galore
Spider Eggs Galore

House Wren nests are often full of spider eggs sacs. When the tiny spiders emerge, they devour nest parasites.

Spiders as Nest Pest Control

House Wrens have discovered an ingenious way of keeping mite levels under control. While the nests of other birds are ridden with the parasites, the House Wren places spider egg sacs inside her nest. When the egg sacs hatch, the baby spiders will have an abundance of mites to eat, and the House Wren nestlings will be thankful. Talk about a win-win.

More About Spiders and Birds

Spiders aren’t always a bird’s best friend, though. The Goliath Birdeater Tarantula does not prey primarily on birds, but it won’t pass up the opportunity if a bird stumbles onto its path. Thankfully, it can only be found in the northern swamps of South America, but even in the United States, bird-eating spiders exist. Songbirds will occasionally become stuck in spiderwebs and die there, because their struggles to escape only further entangle them. Sometimes a spider will cut the bird free, then repair its web.

Warning! No Fly Zone.
Warning! No Fly Zone.

This zigzag pattern called a stabilimentum is thought to make the web more visible and prevent birds and other animals from ruining a perfectly good web.

Because web repair is costly in time and in nutrients, spiders such as the garden orb weaver will weave a visible pattern into their webs, called a stabilimentum. Many arachnologists believe the stabilimentum serves as a warning to birds and other large animals that the web is there, thus saving the spider the trouble of repairing it when a large animal comes crashing through. It has been documented, however, in rare cases, that a golden orb weaver will take advantage of a snared bird, encase it in silk, and eat it. These predation methods are mostly opportunistic, and always involve smaller birds such as hummingbirds and kinglets.

When it comes to spiders, we may want to squash them on sight, but clearly the benefits of having them around outweigh the dangers. So take the time to hug your creepy-crawly neighbors today…or maybe not.

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  1. Paula says:

    Is it a good idea to imitate the wren and introduce spider casings, (or spiders), into nests we are monitoring, such as an Eastern Bluebird nest? It sounds like it would be a more wholesome solution than using pyrethrin, which I have read is recommended for parasite prevention in a nest-box. The pyrethrin solution I have emits such a pungent odor that I stopped using it, fearing the effect the fumes would have on the young.
    Thanks! Interesting article.

    • Robyn Bailey says:

      Hi Paula. I don’t usually see mites in my bluebird boxes; normally just the blowfly larvae which are too big for baby spiders to eat. But even if you do have mites, NestWatch doesn’t recommend introducing anything into a bird’s nest. We recommend just letting the birds handle it, as the parasites aren’t usually lethal. Nature knows best.

      • Paula says:

        Thank you, Robyn. You’re right, I think the second and third broods get the blowfly larvae in our boxes, but mites are not likely a problem, thankfully. Seeing these larvae in the bottom of the nest was a cause of concern to me at first, but the bluebirds have fledged many a healthy chick without the use of pyrethrin.

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