Asian Hornet Harps

A harp is not a bait trap. It is a grid of electrified wires that stands in front of the hive entrance: tempered wire of Ø 0.30 mm, all but invisible, spaced 20 mm apart. That spacing is the whole mechanism — a bee flies between two wires without touching them, an Asian hornet is wider, closes the circuit and drops.

Selectivity is not a property of the device

This is the most misread point. It is often quoted that in bait traps only 1% of the catch is Vespa velutina — work by the University of Vigo and the University of Santiago de Compostela — and the conclusion drawn is that trapping kills blindly. Yet Asturias's queen-trapping programme, with the right trap and lure and in its season, closed 2025 with 109,000 hornets caught and this breakdown: 90% Vespa velutina, 7% Vespa crabro, 3% other wasps and a negligible fraction of bees.

So the reading is not "this device is selective and that one is not": selectivity comes from the whole set-up — trap, lure, time of year and location. Sweet bait in a wide mouth in August kills everything; a specific lure in spring, in an area with nest-producing queens, lifted in June, barely touches anything else. By that yardstick the harp catches 68% velutina and a well-built entrance trap reaches 95% (25,000 catches measured by the University of Girona). The harp is not the most selective thing out there: it is the most selective thing you can buy ready-made and have running the same afternoon.

What the harp does not fix, and what it does

It does not destroy the nest. Workers range up to 3 km — confirmed by marking them — so the pressure at your entrances does not come from one nest and is not settled at the entrance: what lowers the population is spring queen trapping. If you find a nest, do not disturb it; report it to the competent authority.

What it does fix is the part that actually costs money, and it is not the bees eaten: it is the colony that stops flying. A queen lays on the order of a thousand eggs a day at peak and the hornet takes them one at a time; as long as the bees keep flying, the arithmetic holds. Once the colony shuts down you lose the August and September matings, the late flow never comes in, and colonies have been measured losing 5 kg in three months. A study by the USC with the Portuguese national beekeepers' federation put a price on it: +15% on feeding, −20% honey production and an average of €13.35 per hive per year. And mind the side effect: with a hornet in front of the entrance, varroa goes unnoticed. Plenty of colonies written off to velutina died of varroosis or of starvation.

Where exactly it goes

The harp goes parallel to the hive entrances — spanning across in front of them, not edge-on — and 30-40 cm from the entrance. That distance is the balance point: any closer and you start electrocuting your own bees, any further and the hornets simply fly around it. The hornet has to be forced to pass through the wires, and pallets or a side net that narrows the gap will funnel its flight into the harp.

The three parts of the system

A harp on its own does nothing. You need harp + electrical module + tray. Starting from scratch, the complete kit (€259.95) brings all three with a solar panel; if your harps are already up, what you are buying is the module.

• How many harps each module powers. This is the figure that decides the purchase and almost nobody publishes it. The 1,500 V modules run up to 5 harps: the universal one (€121), which takes mains via USB, a 6 or 12 V battery and any panel from 5 to 32 V, and the 10 W solar one (€145). The 2,200 Vdc modules run 8-10 harps: the standalone board for your own battery (€69.95, IP55 enclosure) and the kit with a 7 Ah battery, 20 W panel and timer (€160).
• Voltage is not enough to decide: check the connector. The Tartago harp works with both 1,500 V modules and also with the standalone 2,200 Vdc board. The one it does not take is the board kit with battery and 20 W panel (€160), which is built for another maker's harps — and it delivers exactly the same 2,200 Vdc as the standalone board, which does fit. A module that will not couple to your harp is the expensive mistake in this category.
• How many harps your apiary needs. One at the start and one at the end of each row, plus one every five hives. With five hives, three harps: start, middle and end. And the trick that genuinely saves money — set two rows with the entrances facing each other and put a single harp in the middle, and that one harp covers up to ten hives. The 10 m leads for chaining harps to one module cost €44.75; a new module runs €121 to €160.
• The tray tells you whether it is sited correctly. The water should hold 4 or 5 bees per 100 hornets. Above that ratio the harp is too close to the entrance — check the 30-40 cm — or badly oriented, and the answer is to move it. It is the only reliable check you have, and it only works if the tray holds water: an electrocuted hornet falls stunned, not always dead, and in the shade it can come round and fly off. And an honest warning: if an electrical fault drops one bee onto the wire, a ball of bees follows it to the same spot — all the more reason not to leave a harp alone for three weeks.
• When NOT to keep them live. Harps work from June to October, when workers hunt in front of the entrances. During swarming and queen mating it is best to switch them off: the virgin queen goes out on her flight and the harp does not discriminate. And move them every two or three weeks, because hornets learn to avoid a fixed obstacle.