Laura Erickson's For the Birds

On Sunday, April 06, I found a spider in my bathroom. Having two indoor cats, spiders have become pretty rare in my house, but this one emerged from the basement or some other winter hiding place just to let me know that spring is really here.

Birders like knowing the names of things. And I just happened to have exactly the resource to help me figure out that this wasn’t just some generic spider, it was a Barn Funnel Weaver. How did I learn this? I’d just bought a copy of Larry Weber’s great new book, Spiders of the North Woods.

Spiders feature enormously in the lives of birds. Intuitively we know that birds can pick up spiders on the ground, and maybe in trees, though on the ground spiders are good at hiding and don’t provide birds with nearly as much food as we might think. But spiders provide a lot of protein for flycatching birds, including species like nighthawks and swallows that feed at high altitudes.

I was amazed when I talked to an airplane pilot who told me he did some collecting of aeroplankton—tiny creatures in the sky from swarms of tiny midges to huge dragonflies and monarch butterflies—and he found that one of the most common things up high is spiders. How is that possible? When baby spiders disperse from the place where they hatched, they shoot out a strand of spider silk which gets picked up on an air current and carries them aloft. This ballooning process carries spiders up up and away—it’s even carried some spiders a minimum of 2500 miles over the Pacific Ocean to colonize Hawaii.

If spiders are important to birds for food, they’re equally important for something else—gossamer. The spider silk they produce has two features that make it a perfect building material for bird nests—it’s strong, and it’s stretchy. Hummingbirds and other small birds are especially likely to use it in their nests. Tiny Ruby-throated Hummingbird females construct a nest about the size of a walnut, with very thick, well-insulated walls constructed mainly of lichens and spider silk. The walls of the nest are thick, but the inside is barely big enough to accommodate two pea-sized eggs, so heat won’t leak out when the mother is incubating. But those two eggs will hatch into babies that each grow to be almost as big as the mother before leaving the nest. This could have represented as big a problem as keeping a human baby in a bassinet until he or she is school-aged, but thanks to hummingbird nest-building materials, the nest literally grows with the babies. As they grow and wiggle and move about, the nest stretches, so by the end of the nesting period the nest is much thinner-walled and wide-brimmed than it started out, yet it never falls apart thanks to the strength and stretchiness of spider silk.

If you want to get started on identifying the spiders you run across, Larry Weber’s book, Spider of the North Woods, is a great way to start, filled with Larry’s photographs and glowing with Larry’s expertise and enthusiasm. I highly recommend it.