Unusually hot weather has caused black flies to emerge earlier than normal, and they are aggressively targeting bluebirds, swallows, and other cavity‑nesting species. Nestlings can be overwhelmed quickly, so prompt action is essential.​​​

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• Apply a repellent: Add 1–2 drops of vanilla extract to the underside of the roof.  (Some monitors also place a tiny drop on the back of each chick when possible.)

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• Use permethrin on the box exterior: Another effective approach is to spray the outside of the nest box with permethrin. Avoid spraying the chicks directly. Focus on the entrance hole, vents, and any open seams or cracks. One application typically lasts for the season. (Video at right demonstrates proper application.)

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• Check boxes daily during periods of heavy fly activity.

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• Remove any dead flies found inside the box.

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• Keep ventilation holes open and ensure predator guards are secure.

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• Keep checks brief to avoid stressing the adults.

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Why this matters

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Black flies can overwhelm nestlings rapidly. Taking these steps can make the difference between a successful brood and a loss.

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We encourage all monitors to stay vigilant during this early‑season surge.