Autumn grass mites: tiny arachnids cause severe itching up to two weeks, German health officials advise
The larvae of autumn grass mites, barely visible at 0.25 mm, secrete a fluid that dissolves skin, causing delayed itching that can last up to two weeks, according to German health experts.
What are autumn grass mites?
Autumn grass mites (Neotrombicula autumnalis), also known as harvest mites, are arachnids, not insects. They inhabit meadows, parks, gardens, and other green spaces. Alex Christian, former scientific head of the Arachnida section at the Senckenberg Museum of Natural History in Görlitz, explained that only the larval stage is parasitic. The larvae seek hosts, primarily small mammals but also humans, to feed on. After feeding, they drop off and develop into non-parasitic nymphs that no longer affect people.
How they bite and cause itching
Unlike mosquitoes or ticks, these mites lack a stinging organ. Instead, they hook onto the skin with their mouthparts and secrete a fluid that dissolves the top skin layer. The host feels nothing while the mite is attached. Christian described the aftermath vividly.
Only when they are gone and these substances are missing, then it itches, and really, really horribly.
The bites appear as reddish wheals. A spokesperson for the German Red Cross (DRK) said the itching typically begins 12 to 24 hours after the bite and can persist for up to two weeks. Commonly affected areas are those with thin, moist skin: feet, ankles, the backs of knees, the waist, and armpits.
- Mite larva hooks onto skin with mouthparts and begins feeding, secreting a fluid that dissolves the top skin layer.
- The host feels nothing while the mite feeds; the larva swells from 0.25 mm to up to 0.7 mm.
- Once engorged, the larva drops off the host and returns to the ground to develop into a non-parasitic nymph.
- Intense itching begins, often described as extremely unpleasant, with reddish wheals appearing on the skin.
- The itching can persist for up to two weeks; scratching may lead to inflammation and should be avoided.
Health risks and treatment
The DRK spokesperson confirmed that autumn grass mites do not transmit diseases, unlike ticks.
Autumn grass mites do not transmit diseases like ticks, but the itching is often extremely unpleasant.
Scratching should be avoided because it can lead to inflammation. The DRK recommends cooling compresses, antihistamine gels, or over-the-counter cortisone ointments to relieve the itching. If the itching lasts longer than two weeks, worsens, or signs of an allergic reaction appear (such as large blisters or shortness of breath), medical advice should be sought.
Prevention tips
The mite larvae measure about 0.25 mm and swell to 0.7 mm when engorged, making them barely visible to the naked eye. People who spend time outdoors are most at risk. Christian advised wearing long clothing, sturdy shoes, and tucking trousers into socks. The DRK spokesperson added that walking barefoot on grass should be avoided. After outdoor activities, showering and washing worn clothing at 60 degrees Celsius helps remove any mites.
Impact on pets
The arachnids can also cause itching in animals. Christiane Bärsch of the German Federal Chamber of Veterinarians noted that dogs, in particular, show strong reactions during the summer months. The same preventive measures, such as checking pets after walks and keeping grass short, can help reduce exposure.
