The Sky’s the limit: how high do flies fly?

PCN is able to share a short communication article ‘House Fly Trap Height Placement’ to provide advice ahead of anticipated peaks in fly activity during the upcoming warmer months.

By: Joseph Diclaro, Phil Koehler, and Roberto Pereira. Entomology and Nematology Department, University of Florida.

A social benefit of being an Entomologist is that people always like to ask questions about insects. Most of the time these questions are simple and have straight forward answers, but every once in a while someone will ask a question that requires a bit more thought. A good example is when the subject of house fly infestation is mentioned. When someone says,

“I just put a fly trap up” the next question usually is “How high should I hang it?” A general response is: “how high is it most commonly placed” On the surface it seems like a simple question but if you sit back and think for a moment you may wonder; what is the optimal height for a fly trap to hang? In some cases the trap design does not leave any choices in height placement. For instance a conical hoop trap made in the early 1900’s was constructed so that it had an entry point 1 inch (2.54 cm) above the ground.

In the past, fly traps have been evaluated extensively for the perfect design. Usually these evaluations are done on farms and other rural areas where filth fly populations are very high. It has been shown that, in this type of environment, the best placement of several different baited traps is with the entry opening 24 inches (60 cm) from the ground. Traps at 24 inches high caught more flies than traps that were placed directly on the ground. This makes good sense because on a farm the house fly attractant is on the ground (manure) and 24 inches leaves enough space for flies to not only fly around a trap but under the trap as well. Depending on the trap type this may allow the bait used in the trap to exert greater attraction to house flies.

Outdoors, 24 inches may be the best height for a fly trap, but most questions these days about fly traps are coming from homeowners and business owners. So what about hanging a fly trap in a building – what is the optimal height? More flies were caught near the rafters in a structure, at 110 inches (280 cm) from the floor, compared to traps at various other levels. However, the other levels tested showed no significant difference in the amount of flies caught between them, even the traps that were near the ground. In order to get a clear answer on how high a fly trap should be hung inside a building, we needed more data, so we conducted a simple experiment. Pieces of white corrugated plastic with a piece of fly ribbon pinned across it (plastic target [3.94 x 3.94 inch;10×10 cm], Figure 1), were placed at different heights.

Plastic target with house flies stuck to it, hung from ceiling by fishing line
Figure 1: 

Figure 1: Plastic target with house flies stuck to it, hung from ceiling by fishing line.
Then we released ~300 house flies in a room 15’6” x 20’ (4.72 x 6.1 m), (Figure 2), with four plastic targets at 3 feet (.91 m). We repeated the procedure with targets at 6 feet (1.8 m) and 8 feet (2.44 m). After testing each height individually, all three heights were tested simultaneously. The flies were released in the center of the room on the existing counter and then left undisturbed for 24 hours with the lights left on.

Figure 2
Figure 2

Figure 2: Visible plastic targets hung near window and cabinet (arrows).
Flies were released on center of counter (box). The targets at 3 ft and 8 ft high caught the most flies (Figure 3), but there was no statistical difference in the number of flies caught at the three heights when they were tested individually.

 

Figure 3
Figure 3

Figure 3: Average number of house flies caught at individual heights after 24 h. No significant differences were observed.
When the plastic targets were hung at all three levels at the same time, the lower plastic target caught half the fly population (Figure 4) but there were no significant differences in the three heights, even when they were tested together. From these preliminary results we concluded that house flies in an indoor environment will travel to a trap no matter what height it is located, as long as it is attractive to the fly.

Figure 4
Figure 4

Figure 4: Average number of house flies caught at heights hung together after 24 h. No significant differences were observed.
These results also tell us a couple of other things. First, that people who work in a room where this type of research is done do not appreciate when 300 flies are released. Second, in enclosed environments, such as a home, an office, or enclosed rearing facilities, the height of the fly trap may not matter much. On a farm, flies fly where the attractant (manure) is located, near the ground. In an enclosed environment house flies will go to the easiest accessible attractant no matter at what height.