The wood wasp parasitic wasp will be the “Insect of the Year” for 2025, a board of trustees has announced. It is easily recognizable by its graceful body and the long egg-laying borer of the female. The insect is particularly useful for forestry because its offspring feeds on the larvae of wood wasps, which are harmful to trees. Because of this ability, the parasitic wasp is specifically released in certain regions to combat the pests.
Since 1999, an independent international board of trustees made up of entomologists and representatives of scientific societies and institutions has chosen the “Insect of the Year” for Germany, Austria and Switzerland. To do this, the experts select an insect from numerous suggestions that plays an ecologically important role. The award is intended to promote knowledge and acceptance of the insect and reduce prejudices.
The parasitic wood wasp (Rhyssa persuasoria) has now been selected for 2025. This species of parasitic wasp can be easily distinguished from other insects by the white spots and the long black-red legs on its black body, which is up to 35 millimeters long. The females also have a noticeable drill that is longer than their body and which they use to lay their eggs. They use the larvae of the wood wasp as a place to deposit them. This is where their name comes from.
Natural pest control by laying eggs
Wood wasp larvae feed on the wood of trees – this damages the tree. “The wood wasp parasitic wasp surprisingly recognizes the trees infested by wood wasps by smell. It doesn’t smell the wasp larvae itself, but the wood-degrading fungi it brings with it, such as the brown tomentose layer fungus, with which the wood wasp larvae can digest the wood,” explains Thomas Schmitt from the Senckenberg German Entomological Institute in Müncheberg. Once a female parasitic wasp has found the perfect spot to lay her eggs, she stretches her abdomen upwards to position the ovipositor vertically on the wood. It then drills into the wood for up to 30 minutes until it finds the wood wasp larva and deposits the egg on the host.
The parasitic wasp larva then hatches from the egg and bites onto the wood wasp larva with its mouthparts. “During the first three larval stages, the ectoparasitoid parasitic wood wasp anchors itself in the infected larva with its long, sickle-shaped mandibles and feeds on the exuding body fluid. In the fourth larval instar, the host larva is then completely eaten,” says Schmitt. This process takes around five weeks. The parasitic wasp larva then spins a cocoon in order to overwinter in the wood without destroying any further wood. Adult wood wasp parasitic wasps feed on honeydew or pine needle sap and are active from late spring to late summer.
The wood wasp parasitic wasp as an international helper
The parasitic wasp is widespread throughout the northern hemisphere. Because of their ability to kill tree-damaging wood wasps without harming the trees themselves, South America, New Zealand and Australia use them to combat the highly invasive blue spruce wood wasp. This once settled on other continents through the export of European firewood and construction wood. The larvae of this insect feed on wood, damaging the trees in which they live.
“The parasitic wood wasp is a prime example of the complexity and beauty of our ecosystems. It shows how even small creatures can have a major influence on nature – the parasitic wood wasp makes a positive contribution to controlling wood wasps, which are problematic for the timber industry,” says Katrin Vohland from the Natural History Museum Vienna. “In this way, the ‘Insect of the Year 2025’ supports forestry, reduces the need for human intervention and the use of chemical agents and can thus promote biodiversity in the long term.”
Source: Senckenberg Society for Natural Research