Mediterranean ants successfully controlled by freezing the soil

Published on
December 22, 2022

Freezing the soil is an effective tool for controlling the Mediterranean Tapinoma nigerrimum ant species. This invasive ant is causing serious problems in and around homes in more and more parts of the Netherlands.

Researchers from Wageningen University & Research, EIS- Kenniscentrum Insecten (an insect research institute) and Tibach (a technical innovation centre) demonstrated the effectiveness of this method during a research project commissioned by the Ministry of Agriculture, Nature, and Food Quality.

Effect of cold temperatures

The researchers investigated how Tapinoma nigerrimum responds to cold temperatures using a pest control method developed by Tibach. The research demonstrated that freezing the soil to a depth of more than one metre is an effective method for controlling these Mediterranean ants.

The researchers do recommend carrying out the intervention during the cold season. This is because ants are very active during warmer weather and more likely to flee the nest, while in autumn and winter they hide deeper under the soil to protect themselves against the cold, so more can be exterminated.

The same method was previously used to control Japanese knotweed. This invasive plant was also controlled by freezing the soil. The method proved to have no adverse effects on soil life and the soil seed bank (the natural storage of seeds in the soil). This method of control also allows the use of chemical pesticides to be drastically reduced.

How does the freezing method work?

Special freezing lances are inserted into the soil around and inside the nests to a depth of one metre. The lances are cooled to a temperature of -35ºC, freezing the surrounding soil. The ants freeze to death and the targeted part of the colony is exterminated.

Tapinoma nigerrimum

This Mediterranean species of ant is turning up in more and more places in the Netherlands. The ants are capable of building ‘super colonies’ that extend up to hundreds of metres, so a single nest can infest houses in several streets. Outdoors, gardens and pavements can cave in above the ants’ tunnels. Indoors, the ants are even more of a nuisance, as they can infest a house from the crawl space to the attic and also nest in cavity walls.

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