Spider folds blade of grass,
Enclosing her eggs and herself
Never to see the sun again.
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| (Click to enlarge) |
A few years ago I spotted some neatly folded grass blades in a clump of
Switchgrass in the front yard. A closer look showed that the grass blade had
been folded twice, the first fold about six inches from the tip and the second
fold brought the tip back up. The edges of the grass were stuck together by
silk, in such a way that they made a small, three-sided purse, with tapered
ends. I found two more grass blades folded in the same manner, so I decided to open
one up to see what was inside.
I immediately regretted doing this. A small
spider with a clump of eggs was inside the little grassy box and it stayed with
the eggs, never even attempting to run. I refolded the grass blade, hoping that
the spider would repair the damage I’d done.
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| Nest found opened after violent thunderstorm. The white material is the silk that fastened the edges of the nest "box." |
In subsequent years I always found at least three of these spider nests
in the same patch of Switchgrass. Most of the time the spider folded the leaf
blade twice to make the nest, but,
occasionally I found one that was made with
three folds.
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| A nest with three folds |
This year I decided it was time to figure out what kind of spider builds
these neat little hideaways. I googled “spider folded leaf nest” just to see
what would turn up. One of the hits on the first page led me to a book with an
illustration of a nest that was identical to the ones I had been finding. The
spider responsible was identified as Clubiona riparia (Riparian Sac Spider,
Bank Sac Spider, Leaf-curling Sac Spider). The biggest problem with applying that
identification is that the Riparian Sac spider is known from riparian habitats
in Canada, Alaska and the northern USA. (Riparian is a term applied to the
wetlands bordering rivers and streams.) Our front yard is definitely not riparian
– we’re at least a mile from the closest river. But the nest illustrated was
identical to the ones in our yard, so perhaps it’s a related form.
The book indicated that the female deposits her eggs
within the nest and remains with them until they hatch or she dies. In the words
of famous entomologist John Henry Comstock, the nest serves, “as a nursery for
the spiderlings and a coffin for the parent.” Other sources repeat this
information with the embellishment that her body provides the hatchlings their
first meal. I couldn’t find any citation to support this information.
Maternal care is known in several groups of spiders. Some jumping
spiders remain with their eggs in a silken cocoon until they hatch. Wolf
spiders carry their egg sac attached to their spinnerets until they hatch; then
the young spiderlings are carried about on the back of their mother. A few
spiders feed secretions from their body to their newly hatched offspring. In
return, the young spiders eat their mother’s body.
The construction of the nest is a bit of spider origami. The two-fold
version is done in such a way that the vascular system of the grass blade is
not damaged. If it were, the blade that forms the nest would dry out and turn
brown, making it conspicuous to predators. Since the blade usually retains its
green color, maybe it’s better to think of the blade being bent, rather than
folded.
I tried to reverse-engineer the nest construction. First, I cut a long,
narrow strip of paper. Then I folded it in half, making the fold so that the
upper end lay at a small angle to the lower end. Then I used a 1 inch long
piece of tape to attach the two edges. Because the fold was not at 90 degrees
the untaped side stays gapped open. This leaves room for the spider. The next
part is tricky: I bent the original upper end backward and slightly twisted, so
that it would cover the space between the free edges of the “box” formed by the
first fold. Then I taped the edges together to make a kind of twisted, three-sided
box. I don’t know if the spider folds the grass blade in this order, but, if
you try to do it, you’ll see how the chamber is formed.
You have to remember that the spider is doing this all from the
inside. It’s like sewing together a sleeping bag from a single strip of cloth
while you’re on the inside, standing on it.
I leave constructing the three-fold version as an exercise for the
reader.
