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Spot, Approach, Destroy: Dealing with Yellow-legged hornet Nests

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The Yellow-legged hornet (Vespa velutina) poses a significant threat to our native bee populations. It’s essential not only to trap these pests but also to destroy their nests. Finding and eliminating these nests can halt the spread and cut off the threat at its source. However, dealing with these nests requires care, expertise, and the right methods.

Spotting the Nest: Detection Methods

  1. Traditional Observations:
    The age-old method of patiently watching and following hornets as they return to their nest. While time-consuming, it’s often surprisingly effective, especially during peak foraging hours in the morning and late afternoon.

  2. Triangulation:
    By placing food bait at different locations and noting the direction in which hornets fly off with it, one can triangulate their flight paths and determine the nest’s approximate location.

  3. Electronic Markers:
    This innovative technique involves capturing hornets, attaching electronic markers, and then releasing them. As they return to the nest, the electronic device signals its location.

Electronic marker Yellow legged hornet
Photo 1. Transponder attached on an Yellow-legged hornet's thorax. ©Scientific reports

4. Thermic Imaging:
Hornet nests, teeming with activity, emit heat. Using thermal imaging devices, especially during cooler evening hours, can reveal the heat source of a concealed nest.

Thermal imaging in detecting nests of the invasive hornet Vespa velutina.
Photo 2. Thermal imaging in detecting nests of the invasive hornet Vespa velutina. ©Insect Science

Approaching the Threat: Nest Destruction Methods

Human-Height Nests: Nests found at human height are relatively easier to manage. They can be encased in multiple plastic bags or containers and then frozen at -20°C (-4°F) for 48 hours, ensuring the hornets inside are killed.

However, many nests are located at higher elevations and are more challenging. Accessing these might require techniques such as pruning, telescopic poles, or even lifting platforms to reach the nest and apply a solution to exterminate the hornets. Regardless of the nest’s location, it’s crucial to engage specialized operators for the eradication. Attempting to destroy the nest alone is strongly discouraged.

Non-Chemical Destruction Methods:

  • Microwave Radiation: This method kills hornets without the use of chemicals, ensuring no harm to other species. The dead hornets and larvae can be safely consumed afterward. However, this technique was abandoned due to its challenging implementation, potential harm to nearby species and humans, and high costs.
  • Lethal Temperature Exposure: This method doesn’t leave any toxic residues and poses no threat to humans or other species. It’s still under experimentation and doesn’t affect hornets outside the nest during treatment.
  • Aspiration: This involves vacuuming the nest until it’s empty, then crushing the bag to kill the hornets, either by pressing or drowning them.
  • Shotgun Shooting: Although this method doesn’t ensure the total destruction of the colony, it has been used by some as an unconventional approach.

Chemical Destruction Methods:

  • Injecting pesticides, such as permethrin and its derivatives or pyrethroids, is a common method. This can be achieved using various techniques, like poles for internal destruction, placing meatballs laced with the chemical in front of hives, applying drops directly on trapped hornets, or even using paintball shots aimed at the nests. However, these techniques can harm the environment as they might expose other insect species and birds to the pesticides, especially if they consume the dead hornets. It’s essential to limit the exposure by removing the nest from the environment within 48 hours after treatment. Pesticide injections are generally reserved for larger, high-altitude nests.
  • Other tested injection products include:
    Sulfur Dioxide (SO2) Injection: This isn’t recommended due to its irritation properties. When it comes into contact with mucous membranes, it turns into sulfuric acid, causing eye and respiratory irritation.
    –Diatomaceous Earth Injection: A white powder that covers and quickly kills the hornets. It has an abrasive action that obstructs the hornet’s leg and wing joints and is highly absorbent, draining the hornet’s bodily fluids. The primary challenge is the same as other methods: the need for rapid nest removal to avoid exposing other species.

Please note that some of the chemical methods mentioned here may not be permitted in all countries. Expert nest removers will be well-versed in local regulations and will select the most appropriate and legal solutions for your situation.

Trojan Horse Technique:

An innovative approach involves using hornets to transport an active ingredient. The idea is to encase a pesticide in a matrix, only to be released when it reaches the nest due to specific conditions like temperature and salivary enzymes. One proposal, yet to be realized, is to transfer an entomopathogenic fungus (like Beauveria and Metharizium). Laboratory tests have been conducted, but field application is still pending.

A Word of Caution

Dealing with Vespa velutina nests is not for the untrained. Their aggressive nature, when threatened, can lead to multiple, painful stings. Even if you’ve detected a nest, it’s imperative to contact professionals to handle the removal. Pest control specialists have robust protective equipment, far surpassing the standard beekeeping suit, ensuring safe and effective nest destruction.

Stay Safe, Stay Informed

While Véto-pharma doesn’t offer direct solutions for nest destruction, we believe in equipping our community with knowledge. Understand the threat, use the best methods to combat it, but always prioritize safety. And remember, the best defense is a community armed with information.

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