Midge trap counts at popular roadside viewpoints are running around four times higher than at ecologically identical sites two hundred metres away, according to a season of standardised sampling.
The habitat is the same. The vegetation is the same. The wind exposure is the same, and in several cases marginally better at the viewpoint.
The difference is the people.
The mechanism
Female biting midges locate hosts primarily by carbon dioxide, detectable over surprising distances, alongside body heat and skin chemistry.
A viewpoint receiving a vehicle every ninety seconds for fourteen hours a day is, from a midge’s perspective, a reliable and continuously replenished plume. Insects accumulate where the cue persists, and the cue persists because the next car is arriving.
The result is a self-sustaining local concentration that exists because of the visitors experiencing it.
“People stop at the busy viewpoint because it is the famous one, get eaten, and conclude the midges are bad this year. The midges are bad at that spot. Two hundred metres along, the same evening, they are a quarter as bad.”
The entomologist running the sampling
Practical consequences
The finding produces advice that is more useful than most midge advice, which historically has consisted of telling people the midges are bad.
Stop somewhere other than the busiest layby. Arrive early or late rather than at the peak of the vehicle cycle. Keep moving, because a stationary group is the plume.
The sampling
- Trap counts at busy viewpoints: around 4x adjacent control sites
- Habitat difference: none measurable
- Peak conditions: still air, dusk, humidity above 80%
- Effect of moving 200m: counts fall by roughly three quarters
- Season: late May to early September
The entomologist added one further observation, offered without prompting. In thirty years of this work, she said, no visitor has ever been persuaded that the midges are not personally motivated.
