Dangers Posed by the Oak Processionary Moth

The oak processionary moth (Thaumetopoea processionea) is a type of moth whose caterpillars are found in oak forests. The most dangerous part of these caterpillars is their tiny hairs, which can pose a serious health risk to dogs. The first part of the moth's scientific name comes from 'thaumetopoein' which is the irritant protein found in its hairs. 

The caterpillars live in large groups and move around the trees in a line, with one following behind the other. The highest risk to dogs happens from May to July when the caterpillars develop their stinging hairs. Both the caterpillars and their nests can pose a threat to dogs.

Learning to identify the caterpillars and their nests is important to be able to react in time to protect your dog. 

The colour of the caterpillars changes with age. The freshly hatched larvae have a dark head and brown body. With increasing age, the body takes on a grey colour. The oldest caterpillars are easier to identify as they have a dark stripe with whitish lines on each side. 

During their third larval stage, which occurs around May or June depending on the weather, they develop fine, short, hollow stinging hairs that cover their entire body. These hairs are particularly dangerous because they contain a toxic substance. The number and length of these hairs also increase with each molt.

Once the caterpillars are older and larger, they migrate along the oak tree and build their nests, where they spend most of the day moulting and only leave them to feed at dawn and dusk. The nests can usually be found on the trunks and branches of oak trees in early summer. They are usually shaped like a dome or teardrop and come in various sizes. When freshly built, the nests are silky white in color, but over time, they change to a brown hue, making them harder to spot.

The moths stinging hairs are equipped with barbs (setae) and contain the problematic protein thaumetopoein. When these hairs come into contact with skin or mucous membranes, they penetrate and attach themselves using their tiny hooks and secrete venom. This venom can cause severe itching, skin reactions such as rashes, fever, and vomiting in severe cases. Additionally, it may lead to eye irritation (conjunctivitis), respiratory issues, and possibly allergic reactions that could escalate to life-threatening anaphylactic shock. In the worst cases, dogs may suffer from suffocation leading to death. Make sure to see a veterinarian if your dog shows signs of these symptoms.

Also be aware that direct contact with the larvae isn't the only danger, as they may shed their hairs as a defence mechanism if they feel disturbed or threatened.

Disclaimer: All our guides are based on scientifically grounded research, current studies, and the expertise of FOUR PAWS experts. If you have any questions or would like to get in touch with our experts, please contact us at research.info@four-paws.org.