Insect Collecting Methods
Malaise traps act as interceptors of flying insects. Crawling insects (and other arthropods) will also climb up the netting if it brushes the ground. At the top is a collection jar with an inverted cone (so insects will crawl in, but can't get out). The collecting jar may contain a dry fumigant, or alcohol, antifreeze, or other "wet" collection fluid. Here are two different designs above.
Intercept traps may take many forms. Above left is what I call an "Aeolian trap" meant to intercept wind-borne insects on lava flows in Hawaii. The construction is a window screen held in place by PVC tubes and suspended over a piece of rain gutter containing soapy water. Insects intercepted by the screen drop into the soapy water. In this case, the trough of soapy water also acted as a pan trap that attracted insects in this dry environment. Above right is a yellow pan trap filled with soapy water. The surfactants in the soap break the surface tension of the water (hydrogen bonding) - otherwise many insects can stand on top of the water. Many people have experimented with different colors. Yellow seems to work best for both leaf feeding "Homoptera", as well as many pollinators and parasitic wasps. The water itself can also be an attractant.
Above left is an ultraviolet light trap. Many night flying insects, particularly moths, are attracted to light (nobody knows why). In this design, the circular bulb (just below the metal lid) is suspended by plastic vanes above a funnel seated in a 5 gallon bucket. The attracted moths fly into the plastic windows and slide down the funnel into the collecting bucket containing a fumigant. This trap is powered by a 12-volt DC deep cycle marine battery. There are also lighter, smaller, rechargeable batteries available. Between the battery and the UV bulb (in front of the battery in this picture) is a photo-cell that detects light. This way the light will automatically turn on when it gets dark and off when it gets light in the morning. Above right is a yellowjacket trap baited with Heptyl Butyrate (an attractant for Vespula). Vent holes allow the attractant to escape, while the inward facing cones allow the wasps to enter the trap which they cannot find their way out of.