The Western Tiger Swallowtail butterfly thinks of Market Street as a natural canyon. The tall buildings and wide street, along with a warm climate and dappled sunlight, simulate the environment of a canyon habitat. The London Plane trees lining the street provide the Swallowtail's larval food source.

Today the Swallowtail butterfly call Market Street home. However, many butterflies do not complete their lifecycle. In its caterpillar stage, the caterpillar naturally falls out of the trees and crawls back up the tree to form its cocoon. On Market Street, most caterpillars get trampled, unknowingly by pedestrians, and do not survive to crawl back to the tree. What if we could "catch" the caterpillars' fall and preserve their habitat? And reveal to pedestrians the natural habitat just above their heads?

The Understory creates a new raised ground to catch the caterpillars along Market Street. The Understory provides a moment for city + ecology to co-mingle, and for pedestrians to see a new view of Market Street.

Step 1: Materials Inventory

Tyvek – 55 yards
Mesh fabric – 16 yards
10'x10'x10' EasyFit Structural Piping System – 1 no. (or trees!)
Concrete mix – 120 lbs.
#0 Grommets – 200
1 1/2" x 1/4" wood – 18 linear ft.
1/16" SS cable – 312 ft.
3/16" nuts and bolts – 78 sets
1/4" shackles – 32
1/16" SS cable ferrules – 16
4" turnbuckles – 16
3 1/2" eyebolts – 28

Step 2: Design

Design elements include an overhead canopy to "catch" the caterpillars – the mesh panels in the canopy allow visibility through the canopy and the Tyvek panels maintain dappled sunlight similar to the effect created by tree leaves.

The canopy is designed to maintain overhead clearance and allow a continuous ADA compliant path of movement.

The canopy is supported by an exo-skeleton structure, and held down for wind protection through cables anchored to concrete blocks.

Step 3: Fabrication

TEMPLATE FOR TYVEK – Create a template for the Tyvek panels per Step 2 Design, and cut panels using scissors. Template dimensions must correspond to EasyFit structural system (if using).

TYVEK GROMMETING – Where a sleeve around an EasyFit pipe is required or where a panel is to be connected to the concrete block, use following steps to grommet the Tyvek panels. Tyvek panels need reinforcement through folding and layering with mesh fabric and tape – create an 18" panel divided into 3" bands and fold and layer with mesh as shown in the image above. Mark location of grommets (at min. 8" on center) and tape both lengthwise along the length of the Tyvek panel, and cross-tape to avoid tearing of the panel when grommeting. Fold the panel inwards (away from publicly visible side) and grommet across the folded layered panel together (mesh + tape + Tyvek). Use a #0 grommet kit and grommet at marked locations.

WOOD STRIPS – At locations where the Tyvek panels form the inner edge of the canopy, reinforce the above step with adding a wood panel before folding the Tyvek. Drill holes through the wood at marked grommet locations, and grommet Tyvek panels after drilling the wood. Secure grommeted Tyvek and wood strips with 3/16" shackles to avoid tearing of Tyvek due to connection to the concrete block through SS cables.

CAST CONCRETE BLOCKS (or substitute with sand bags) – Pick a form for casting the concrete – these instructions use a plastic container. If using a plastic container, apply a thin layer of Vaseline to prep the container. Mix and pour the concrete into the formwork per directions on the concrete mix bag. Place eyehooks into the concrete as it starts to set, to allow a SS cable connection to the Tyvek. Allow to set over the period indicated on the concrete mix bag. Once set, cut through the formwork and place the cast concrete block in a secure location.

SS CABLE – Measure and cut the SS cable into pieces of desired length. Pass the SS cable alternatively through a grommeted edge on the Tyvek panel and an eyehook in the concrete block. Secure on each end using ferrules and turnbuckles.