Wild Ideas: Tiny predators enjoy buggy year

At least a few native predators have been spotted munching on brown marmorated stink bugs (BMSB), as well as numerous other native insects that have proliferated this year.

In line with last year, the first large wave of BMSB showed up at my house on the day before the autumnal equinox. Although they disappeared the next day, dozens started to appear on my screens when the weather turned drier and warmer.

Like Gulliver, but with a more unfortunate end, this green stink bug is surrounded by Lilliputian predators — in this case, flies and a micrathena spider. The web belonged to a barn spider, closer to the size of the stink bug (about .75 inches long), which was hiding nearby. Photos by Pam Owen.
Like Gulliver, but with a more unfortunate end, this green stink bug is surrounded by Lilliputian predators — in this case, flies and a micrathena spider. The web belonged to a barn spider, closer to the size of the stink bug (about .75 inches long), which was hiding nearby. Photos by Pam Owen.

I haven’t yet checked with researchers monitoring the bug to see if its numbers this year were as large as projected, or the extent of damage it did, but the numbers seem similar to me so far. While research continues on the most promising biological control of BMSB, a parasitic wasp, interest in the bug seems to be growing among our own native invertebrate predators. From praying mantises (see the photo on page 1) to spiders, many have been seen dining on the bug.

Most of the BMSB that had overwintered in my house had left the house and the yard by late spring. However, throughout the summer I found loads of various instars of its cousin, our native green stink bug, feeding on the sunflowers I’d planted on the south side of the house, and much fewer scattered around on native plants.

One day I found an adult green stink bug in an orb weaver spider’s web, wrapped up tightly in silk. A tiny arrow-shaped micrathena spider (Micrathena sagitata), along with some equally diminutive flies, were swarming around the victim, but I knew that small spider didn’t build the large web. The web was suspended between two shelves of an outdoor étagère on my deck, and when I kneeled down to take a photo, I saw the real owner — a fat barn spider (Neoscona crucifera, named for the cross on its back). She was hiding under the top shelf, at the end of one of strands of silk supporting the web.

A white-banded crab spider, with a body that’s only about one-third of an inch long, scores a worker bumble bee.
A white-banded crab spider, with a body that’s only about one-third of an inch long, scores a worker bumble bee.

Only the female barn spider weaves a web, and she usually hangs around in the middle of it, waiting to feel the pull of prey caught in it, when they quickly move out to immobilize the prey, wrapping it in a silk cocoon. When a predator shows up, they race to the far end of their web, which for millennia were usually attached to tree and bush limbs. They draw their legs together and lie quietly under the limb, their brown coloring serving as camouflage against it.

The dozen or so barn spiders out around the deck anchored their webs to the eaves, the deck railing, my favorite chair, plants and even the hummingbird feeder. One even attached her web to the storm door. Every time I went out the door, she’d display the classic response to predators, only in this case she scrunched herself up against a white door, where she didn’t exactly blend in.

I’m seeing a growing number of BMSB ensnared in barn spider webs this year and, while last year I saw the spiders ignoring the bug or even cutting it out of their webs, this year they’re eating it. Along with the stink bugs, flies, moths and other small invertebrates, I found two young skinks, measuring about three inches, wrapped in silk in separate webs. I managed to rescue one, carefully removing the sticky silk from its head and body and turning it loose in my herb garden. Unfortunately, I didn’t get to the other one in time. While it looked like it was napping in a silk hammock, it was dead.

There have also been tons of another micrathena species, the spined micrathena (Micrathena gracilus), in forests this summer. The females look like they’re carrying around a bag of thorns on their butts. These tiny spiders like to build their webs on low bushes, stretching them across an opening, including trails, to catch flying insects. When walking through the forest, I try to spot the webs and duck under them, but frequently don’t see them in time, ending up instead with them stuck to my hair or face. One strategy that I’ve found to help keeping them off me is to hold my hiking pole in front of my face.

A large (more than an inch long) red-footed cannibalfly, in the robberfly family, munches on a coreid bug, which is almost as big as the fly is.
A large (more than an inch long) red-footed cannibalfly, in the robberfly family, munches on a coreid bug, which is almost as big as the fly is.

By regularly inspecting the leaves and flowers around the yard, I’ve been able to observe the predator-prey relationship with yet another small arachnid — the white-banded crab spider, whose body is about one-third of an inch long. I found several well camouflaged on yellow narrowleaf sunflowers and goldenrod.

The spider is brown, with either white or yellow bands, depending on the flower. It’s unclear whether the spider can change its color to match its background or its mother just lays her eggs on flowers that match her color, and thus the color of her young. Either way, the spider sits quietly, its crab-like legs held wide, while it wait for insects feeding on the flower to get near enough to be grabbed. I saw several small worker bumble bees meet their doom in the embrace of these spiders.

Rounding out the list of interesting invertebrate predators around the yard this summer was the large red-footed cannibalfly, whose fierce appearance is somewhat diminished by what looks like little red mittens on its feet. With a body just over an inch long, these killers can easily take down coreid bugs that are almost as big as the fly.

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Pam Owen
About Pam Owen 278 Articles
Writer, editor, photographer, and passionate nature conservationist living in Rappahannock County, in the Blue Ridge Mountains of Virginia. Two favorite quotes: By E.O. Wilson, who coined the term "biodiversity," "Nature holds the key to our aesthetic, intellectual, cognitive and even spiritual satisfaction”; by Douglas Adams, “I love deadlines. I love the whooshing sound they make as they pass by.”