Who's Hiding in the Tapestry?

From a distance, the forests of July look like a lush tapestry of green. But when you step into the loosely woven strands and take a closer look, the leaves are etched with feeding trails, dissected by holes of all shapes and sizes, and covered with the debris of life. It’s a principle of ecology, of course, that every Being is food for someone else.

Cattails, for example, are food for me! Before their flower spikes explode with pollen and become those brown sausage-shaped seed heads, the dense cylinders of their male flowers are a tasty green vegetable. Simply husk them like sweet corn, boil for 10 minutes, and eat with butter and salt. Just like a corncob, there’s a central stem you must nibble around. In Northern Wisconsin, this part of the plant becomes edible in late June.

Harvesting the male flower spike on a cattail. 

A few weeks ago while I was tromping through a cattail stand to harvest dinner, I noticed that some of the cattail leaves were folded over at the tip into a triangular origami box. I set down my bag of flower spikes and used both hands to unfold the leaf. White silk in the seams stretched and tore. The inside was lined with sheets of silk as well, and hidden below this gossamer blanket was a cluster of beige eggs. In a flurry of legs, someone small and brown escaped from the back corner of the box and dropped to the ground. Who had I disturbed?

The next origami leaf I opened much more slowly, and was rewarded with the sight of a pretty little spider covered in silky brown hairs. She stared at me with her ebony face from beyond her pile of eggs.

Riparian sac spiders fold a cattail leaf into a little origami home in which to guard their eggs. Photo by Emily Stone.

All spiders can make silk, but riparian sac spiders like this one don’t build webs. To hunt, they wander through the night, hoping to stumble on an insect or arthropod the right size for their next meal. When a female is ready to lay eggs, though, she finds the leaf of a monocot—plants like grasses or lilies with parallel venation—and bends it around herself in a clockwise direction. She uses silk to hold everything tight and to line the enclosure, then lays her pile of eggs. The leaf isn’t crimped; it remains green and living.

This tidy structure has been described as both a nursery and a coffin. The mother spider will never leave the structure again (except if disturbed by a curious naturalist). Instead, she guards her eggs against the marauding hunger of other female sac spiders. By some accounts, she dies just before the eggs hatch, and the young consume her body as their first meal. It is the ultimate maternal gift.

Sac spiders as a group are common around the globe, and this particular species has been found in Russia, Mongolia, China, Japan, across the Northwoods, and in Cable, Wis.

In looking up information on the Bug of the Week blog by Kate Redmond, I discovered that sac spiders are classified as “leaf folders,” while other leaf architects are “leaf rollers” or “leaf tiers.” All of these insects and spiders use silk that contracts as it dries to shape leaves into shelters.

S. W. Frost, in the 1942 book Insect Life and Insect Natural History, described that “As the strands dry, they shrink and pull the edges of the leaf inward. New and shorter strands are then spun which in turn shrink and pull the edges of the leaf closer together. This is continued until the edge of the leaf is drawn completely over and is fastened with other strands of silk…”

I set out to find examples of the other two leaf architects. It didn’t take long. While walking a section of the Superior Hiking Trail, I spotted large-leaved aster leaves with one edge curled inward toward the midrib. Brown trails through the tissue indicated that the homeowner was mining the leaf material from inside their hidey-hole. I opened one to discover a sprinkling of black frass (poop) and no resident. I decided not to disturb anymore. Micro-moths in the family Tortricidae are some of the most common leaf-rolling architects, and are my top suspects. This group includes spruce budworm, a pest who had sewed fir needles together nearby.

A leaf rolling insect has used silk that shrinks as it dries to construct a shelter in this large-leaved aster leaf. Photo by Emily Stone.

Spruce budworms are leaf-rolling moth larvae likely related to the architect of the leaf above. They are currently killing quite a few fir and spruce trees in Northern Minnesota. 

Photo by Emily Stone.

In a rocky section of trail, a patch of pearly everlasting leaves caught my eye. On several plants a few of the topmost leaves had been sewn together into a messy vase. Without even opening the structure, I knew that this was the work of a spikey black caterpillar who will metamorphose into an American painted lady butterfly. They scrape pale fuzz off the leaves’ surfaces to line their nest, and also munch on the inner walls of their home.

American painted lady butterfly larvae sew pearly everlasting leaves into a vase-shaped hideaway. Photo by Emily Stone.

The hiding caterpillars above will metamorphose into this beautiful American painted lady butterfly. Photo by Emily Stone. 

Everywhere I looked, the signs of leaf-eaters abounded. And then, in a flash of feathers, a bird dove into a bush. Behind the screen of twigs, a male chestnut-sided warbler hopped nervously with two different colors of caterpillars dangling from his beak. When he sensed my focus had strayed, he dove away to his nest. Those larvae were almost certainly leaf-eaters, and they were about to become birds! The abundance of summer is a great time to witness ecology in action.

Can you spot the male chestnut-sided warbler with two caterpillars in his mouth?
Photo by Emily Stone. 

Emily’s third book, Natural Connections3: A Web Endlessly Woven, is available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too.

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Our Summer Calendar is open for registration! The Museum’s new exhibit, The Wetland Way is now open! Discover how life thrives at the intersection of soil and water, and why we must care for these special places as they care for us. Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.