In a survival situation, efficiency has to become a priority. Hunting, fishing, and foraging are all important activities, but they take focus and a lot of time. By using traps and snares, you can multi-task. While the trap does your hunting for you, you can divert attention to your shelter, fire, or rescue.

In this instructable, I will show you how to make an easy and effective crawdad trap out of trash. It takes about one minute to build, shouldn't cost you a dime, and really works! At the end of the day, you'll have some freshwater lobster and you may not want to be rescued.

Step 1: Supplies

You only need two things here: a plastic bottle and a knife or other sharp implement. If you're without a knife, make a sharp lithic flake by smacking two rocks together. Bottles such as these, unfortunately, can be found lying around next to roadways and, sadly, even floating down rivers. Any plastic bottle will do, although I prefer the type shown here, with ridges on the shoulder.

Step 2: Cut the Top Off the Bottle

Next, cut the top off the bottle. Using your knife, make a horizontal incision that runs all the way around the bottle. The cut should be about 1/3 of the way down the bottle. Most importantly, make the cut in a "ditch," between two "bumps" in the plastic. The bumps above and below the cut should be roughly the same size. Also, remove the bottle cap, if there is one.

Step 3: Re-assemble

Here's the fun part. Take the top 1/3 that you just removed. Rotate this funnel-shaped part 180 degrees. Insert this part, neck-first, into the bottom. Press the two parts together until the "bumps" pop together.

Step 4: Deploy and Enjoy

Place a small piece of bait inside the trap. The best would be a morsel of rancid meat, such as from roadkill. Submerge the trap in a stream or lake. Placement should be in fairly shallow water, near a bank, and not in a swift current. If there is any current, place the trap's funnel end downstream to keep the trap from filling with sediment. To keep the trap in place, lean a flat rock on it.

Crawdads will smell the bait and enter the trap. Once inside, they are unlikely to manage an escape. When you've caught one (or several), remove the trap from the water. Disassemble the trap and remove your dinner, which can be boiled or roasted.

Step 5: Options

Not all bottles have bumps and ditches, meaning that the "cut and snap" technique won't always work. If you need to secure the two bottle haves together during reassembly, you can do so by way of "stitching."

In the illustrations shown here, the bottle has been reassembled. Holes were then poked through both plastic walls, using an old nail, piece of wire, or your pocket knife. Some type of string or wire (e.g., shoelace) can be threaded through the holes in order to secure the bottle halves together. You could also use toothpick-sized twigs to secure the bottle halves.

Well, there you have it! If you've enjoyed this instructable, please consider voting, as I've entered it in the Survival 'Structable contest. Thank you!