Pitfall Trap Jam Jar

Design Information

Pitfall traps are traps that are mostly buried to catch crawling critters moving along the ground. Depending on where you live you can expect to catch a wide number of different critters. 

The trap fits a standard 8cm by 9.5cm glass jam jar with 6 thread points (it may not fit 4 thread jars). Typically, a pitfall trap is made using a container like a yogurt pot, with a small hole punched in the base for drainage, and then buried up to the lip in soil. Occasionally with a rain cover fashioned over the area. This has some issues, the rain cover may be knocked, the opaque sides of the jar limit observation and the trap becomes an all you can eat for certain predators like hedgehogs. With this design the rain cover friction fits into the central slot and the radiating spokes serve as a barrier, allowing bugs to fall in while preventing larger mammals like hedgehogs from scavenging the trapped insects. Its not foolproof mind, it can't keep out rats, and a determined cat will pry off the rain cover if so inclined. 

If you would prefer to print just one part, you can use the enclosed option, which has more rain shielding as well preventing cats from being able to knock off the other parasol design cover. 

Printing & Assembly

No supports should be necessary. When printing, ensure that the base is positioned with the threads facing upward, and the cover is printed with the central pole facing upward. For the base, a 70% fill worked well for me, while a 20% fill was sufficient for the cover. 

From there screw the base onto your jam jar, making sure its a good fit. The cover should then slot in the central hole, there is a 0.2mm tolerance built into the model so depending on your printer for a better fit you can bump the model size up to 101% or down to 99%. If you find its a bit loose you can add a little bit of adhesive in the slot hole, if you want to still be able to take it apart use something like bluetac or line the bottom with tape or gauze.

To assemble the trap, screw the base onto your jam jar, ensuring a snug fit. The cover should then be inserted into the central hole. The model incorporates a 0.2mm tolerance, you can bump it up or down a percent to vary the fit depending on your printer. If you find that the fit is slightly loose, you can add a small amount of adhesive, tape or gauze in the slot hole.

The enclosed option prints curve down and simply screws in place without any other assembly needed.

How to use

Once assembled, use a small trowel to dig a hole the size of the jar. Generally, a larger hole provides more flexibility and options. Place the jar into the hole and make sure to flatten the dirt as much as possible, ensuring that the lip of the jar lid (where the bugs will enter) is level with the ground. It is crucial to achieve a flat entrance surface; even a few millimeters of the jar being too high can cause passing bugs to go around it instead of directly over the top. To be cautious, it's recommended to have the jar lip a few millimeters lower than the surrounding dirt level.

For optimal results, place the jar outside just before sunset and collect it shortly after sunrise. Most ground-dwelling critters are either crepuscular (active during dawn and dusk) or nocturnal (active at night), so this time frame provides the best opportunity to capture interesting creatures. Make sure to retrieve the jar before the sun shines directly on it or before the heat of the day significantly warms it up. Some more tips if you are having trouble;

• I generally advise against baiting the trap, as it tends to attract various unwanted critters such as rats and cats. However, if you insist on using bait, a small amount of peanut butter goes a long way.
• Avoid using the trap when rain is predicted. While the rain cover helps prevent droplets from directly entering the jar, it does not protect against splashes. Due to the need to place the jar low in the ground to capture bugs, heavy rain can potentially flood the trap with streams of rainwater.
• If you find that you are consistently capturing a single, rather fat spider or other predatory species, you can try adding a small stick that goes from the bottom of the jar and extends out through one of the slots. This modification allows more of your catches to escape but can help the predatory species move on instead of remaining in the trap and enjoying the buffet until you release them in the morning. You can also leave it out for shorter periods of time. Avoid placing it near ant nests or ant highways.
• If you find that you are not catching many bugs, try moving the jar to a few different locations. It can be challenging to identify spots where bugs commonly traverse. If you are still not having much success even after changing the jar's position, you can try sanding the slopes around the slots or using a finer layer height when printing. It's possible that bugs are clinging onto the filament layers to avoid falling into the trap.

If you need help identifying your captured critters consider the mobile app Seek, it's aimed at children but can give fairly reliable results. If you want the exact specific species, or just want to help science, you can post a photo and the location on iNaturalist or another citizen scientist website logging wildlife populations.