Halloween 2018: Realistic Giant Spider

For Halloween 2018 I created a large, realistic spider; I've seen a number of giant spider builds, and while all were impressive, because my father is an entomologist and taught me about insect and arachnid anatomy I was never really satisfied with their inaccuracies and strove to do better. I think I largely succeeded, although there were a number of changes from my original vision to accommodate challenges that arose during the build and time constraints due to not starting until early October and poor weather limiting the amount of time I had to work on it. The spider ended up with a legspan of over 11 feet and was over 8 feet from the end of the abdomen to the tips of the pedipalps, and over 3 feet tall.

The main parts to get spider anatomy correct are:

  • Cephalothorax (body section with the head and legs)
  • Abdomen (largest body section)
  • 8 segmented legs, not at 90 degree angles to the ground
  • 2 pedipalps, smaller appendages in front of the legs
  • Mandibles with claws/fangs
  • Minimum 4 eyes (I went with 6)

Below is the materials list, which is a rough approximation as the changes I made during the build make coming up with an accurate list difficult. I went with 3/4" PVC pipe for the majority of the build to keep pieces standard and as the pool noodles I bought had a 3/4" inside diameter.

MATERIALS

  • Skeleton/Base
    • 3/4" PVC pipe (48 feet for legs + 10 feet for cephalothorax + 10 feet for supports)
    • 1/2" PVC pipe (12 feet)
    • (8) 3/4" PVC 90 degree couplers
    • (25) 3/4" PVC 45 degree couplers
    • (8) 3/4" PVC straight couplers
    • (3) 3/4" PVC T couplers
    • (6) 3/4" PVC cross couplers
    • (4) 3/4" x 1/2" 90 degree couplers
    • (4) 1/2" 45 degree couplers
  • Body, Eyes, & Skin
    • (6) pool noodles
    • (2) 6 foot 1/2" diameter foam pipe insulation
    • (8) 6 foot 3/4" diameter foam pipe insulation
    • Hardware cloth
    • Chicken wire
    • (2) 24" latex balloons
    • (4) poster board sheets
    • (8) plastic drop cloths
    • (15) cans Great Stuff expanding foam
    • (2) large plastic ornaments
    • (4) small plastic ornaments
    • (6) cans gloss black spray paint
    • Wood board (I used a 1x6 2 foot long project board)
    • (2) pipe flanges
  • Other
    • PVC cement
    • Heat gun
    • Wire cutters
    • PVC pipe cutters
    • Zip ties
    • Masking tape
    • Duct tape
    • Plastic bags
    • Fencing tension wire

Step 1: The Base Structure

The main "spine" is a a series of PVC cross couplers with connections for the legs on each side, as seen in the first photo. I did make two major changes after that photo, however. First, the front row was shortened on each side, as these were the connections for the pedipalps and I wanted them closer to the eyes (see third photo). Second, I added two T connectors, one close to the middle and one at the back, with the 90 degree angle facing down, so I could attach hidden supports underneath to keep the body off the ground.

In keeping with accurate spider anatomy, in the first photo the four pipes off to each side act as the coxa part of a spider's legs, while the vertical pipes off them, where the separate legs will attach, act as the trochanter part of a spider's legs. The part in front with the T coupler is where the mandible supports were attached, as can be seen in the third photo.

The legs themselves are constructed as follows:

  • a 45 degree coupler for attaching to the body
  • an 18" length of 3/4" pipe for the femur section of the leg, with a pool noodle cut to length
  • another 45 degree coupler connecting the femur to the tibia
  • an approximately 15" length of 3/4" pipe for the tibia section of the leg, with foam pipe insulation cut to length
  • another 45 degree coupler connecting the tibia to the metatarsus
  • an approximately 15" length of 3/4" pipe for the metatarsus section of the leg, with foam pipe insulation cut to length
  • a straight coupler for connecting the metatarsus to the tarsus
  • a final 12" length of 3/4" pipe for the tarsus section of the leg, of course with foam pipe insulation cut to length

The pedipalps were constructed at the same time in a similar manner:

  • a 45 degree coupler for attaching to the body
  • an 18" length of 1/2" pipe for the first section of the pedipalp, with foam pipe insulation cut to length
  • another 45 degree coupler connecting the two pedipalp sections
  • a 15" length of 1/2" pipe for the section section of the pedipalp, with foam pipe insulation cut to length

The mandibles were constructed with two of the 3/4" x 1/"2 90 degree couplers, with 4" sections of 1/2" pipe leading to 45 degree couplers connecting the mandible structures.

Step 2: The Abdomen

To get a large enough structure for the abdomen, I used two 24" diameter latex balloons, then connected them with poster board strips and duct tape. Once that was complete, I covered it with Great Stuff expanding foam (pro tip: Home Depot has 16 ounce cans vs the 12 ounce cans Wal-Mart and Lowe's carry). Not much else to say about it, it's a time consuming process that took several days of spraying a section, waiting for it to cure, rotating, and repeating.

Step 3: Skinning the Spider

The spider needed a uniform look to tie it together, which I accomplished using the plastic bag corpsing method. Instead of plastic bags, however, I used 0.5mm 9' x 12' plastic painter's drop cloths. The legs each used about half a drop cloth each, and I used a couple on the abdomen to smooth it out.

After wrapping the legs, pedipalps, and abdomen with the drop cloths, I used a heat gun to shrink it tight, which also gave it a more organic look. The wrapped, pre-paint legs and abdomen can be seen in the photos, as can the post-paint, glossy black legs.

Step 4: The Cephalothorax

By the time I got to this point it was crunch time, and I unfortunately didn't take enough photos of the process, but it was relatively straightforward.

I cut 2 approximately 2 foot lengths of hardware cloth, cut holes for the leg attachments, and attached them to either side of the back half of the cephalothorax. I then bent them together, zip tied them around the PVC pipe at the back, and folded them together over the top and zip tied them into a rough form. I did much the same for the front half using several layers of chicken wire, folding and twisting the wire into a close enough shape and inserting the eyes.

For the mandibles I cut a couple of 1 foot high lengths of chicken wire, and used the curvature from them being on the roll to form them into the mandibles. I duct taped a couple of one foot lengths of fencing tension wire to the PVC mandible supports for the fangs, then stuffed the chicken wire mandibles with plastic bags to give the Great Stuff foam something to stick to.

At that point it was down to covering everything with the Great Stuff foam, which I also used to secure the PVC pipe supports to the flanges on the wood board. It isn't pretty, but it keeps the spider upright and is far enough back to be hidden from casual view.

After the foam cured I wrapped the cephalothorax with plastic drop cloths, shrunk it using the heat gun, and painted it as well. The eyes deformed some because of the heat as they were also plastic, but at night it doesn't really stand out.

Step 5: Assemble & Display

So here's the finished spider in all its glory. It got rave reviews from everyone who came by, with a number of people posing for photos with it. I actually didn't get the abdomen attached in time, but I included it from a couple days after. To attach it I cut a hole through the foam and slid it into a PVC pipe attached to the back of the cephalothorax; in the photos it's supported by a Home Depot bucket, but for next year it'll also have a support like the ones holding up the cephalothorax. The spider breaks down easily, with the legs, pedipalps, and abdomen detaching.

While I didn't have the time to do it this year, I'll be adding broom bristles to it for hair, and most likely adding LEDs to the eyes to give them a glow. The fangs will probably get beefed up to stand out more as well, possibly with UV reactive paint.

I hope you've enjoyed my first Instructable, and I'd love to see photos of any giant spiders you make!

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