Constructing the trap
There are two varieties of wasp trap that are easy to make and work on the same premise. That premise being an easily accessible opening to enter the trap and a less accessible opening to leave, with nowhere for the wasp to land and take off inside the trap.
Essentially a wasp or similar winged garden pest is attracted to the trap by the sweet smelling bait, flies in to investigate and lands in the solution inside, unable to escape. If they don't land immediately in the solution, they find the exit difficult to locate because it is directly above them, and most insects struggle to fly in straight vertical lines.
The first variety of trap simply requires a large empty jam jar, a screwdriver or knife and some bait. To make this kind of trap simply cut a hole in the lid of the jar large enough for wasps to get through, fill the jar with bait, replace the lid and place somewhere where wasps will be attracted. Ensure that the hole is large enough for a wasp to crawl through but ideally not large enough for them to easily fly through. This lessens the chances of them being able to fly back out once inside.
The second variety is essentially the same but are made using an empty two liter soda bottle instead. Simply cut the top third of the bottle off and place it inside the bottom half with the bottle top facing to the inside. This creates a funnel that once again stops insects from being able to find their way out easily. The funnel can be secures in place either using sticky tape or several pins pushed through both layers of plastic. The benefit of this type is that it can also be hung from trees near nests more easily and that it can hold more bait.
Choosing the bait
In general, any sticky and sweet liquid will usually do the trick. A little jam mixed with water works well, as does maple syrup, wine or beer with a little sugar mixed in with it or even fruit juices.
Depending on which version of the trap you intend to make, it can also be made even more effective by adding a little vaseline spread onto the inside edges of the jar or bottle. This ensures that nothing can gain a foothold on the inside of the glass as some flies are able to. If spread thickly enough this will also help ensnare insects and bind their legs together, resulting in them falling into the liquid at the bottom all the sooner.
A good amount of bait to use is enough to give at least a couple of centimetres of liquid at the bottom of the trap. This ensures that insects caught in the liquid won't be able to escape and that numerous wasps will fit in the trap before it needs to be re-baited.
If you are eager to avoid killing other flying insects such as hoverflies and bees for example, using meat as a bait is also an option. This attracts wasps and hornets but not bees or certain types of flies.
The danger of a protein based trap is that if left overnight it may attract bigger animals such as raccoons, rats and the like which can break the trap open.
Setting the trap
Once the trap is set up, simply leave it in an area frequented by wasps and wait for them to take the bait.
The best places to put the trap are usually sunny spots in the garden, although never too close to the house due to the fact that there will be more wasps and other flying pests flying around than normal near the trap.
After a few hours the trap should be checked, by which time it will likely contain several dead wasps. If the number of wasps and other assorted insects is large enough that the liquid at the bottom has become escapade, the trap should be cleaned and re-baited.
Similarly after a few hours the bait will tend to lose its aroma and won't attract pests as easily. Once again when this happens the trap can be cleaned and the bait replaced.