Hay mites, often belonging to the Acaridae family or the Pyemotes genus, are minute arachnids that are pests of stored products. These organisms are frequently mistaken for other common household mites or simply dismissed as moving dust particles due to their exceptionally small size. Understanding their physical traits and environments is essential for identifying their presence and distinguishing them from other nearly invisible fauna.
Physical Characteristics and Size
Hay mites are minute, measuring between 0.2 and 0.5 millimeters in length. Most adult mites could fit onto the head of a pin. The straw itch mite (Pyemotes tritici), a common species, is about 0.2 mm long, though a pregnant female can swell dramatically to 1.6 to 2 millimeters, becoming visible as a tiny, pale speck.
Their color is generally translucent, pale white, or cream, and they lack distinct coloration. The body is soft, unsegmented, and typically oval or globular in shape. Like all arachnids, adult hay mites possess eight short legs, allowing for rapid movement across surfaces. A characteristic sign of a severe infestation is the appearance of a “dust cloud” of moving mites when infested material is disturbed.
Common Habitats and Sources
Hay mites are classified as storage mites because they thrive in environments containing dried plant material and high moisture. Their primary habitat is stored commodities such as hay, straw, grain, dried grasses, and animal feed. The mites feed on molds and fungi that grow on these materials, particularly when the moisture content exceeds 13 to 15 percent.
A high relative humidity, typically above 65%, is necessary for their rapid population growth and survival. Infestations often originate in agricultural settings like barns or silos. Mites can then be carried into human dwellings on contaminated materials, including dried flower arrangements, pet food, or bales of hay used for seasonal decorations. When their primary food source becomes scarce, the mites disperse.
Impact on Humans and Animals
Exposure to hay mites often leads to “hay itch” or “straw itch,” which is a form of contact dermatitis. The straw itch mite does not feed on human blood but will bite when it makes contact with skin, injecting a paralyzing toxin intended for insect prey. This exploratory biting results in small, intensely itchy, red welts, often with a tiny blister in the center.
These bites typically appear on parts of the body pressed against the infested material, such as the trunk, arms, and back. Storage mites from the Acaridae family can also cause skin irritation through contact with their bodies or waste products, which contain potent allergens. Individuals exposed to large populations of mites or their fecal matter may experience allergic reactions, including respiratory issues like asthma. In livestock, the presence of mites causes intense itching, leading to scratching and reduced feed intake.