Mites are tiny arachnids, closely related to ticks and spiders, belonging to the class Arachnida. With over 55,000 identified species, they occupy nearly every terrestrial and aquatic habitat globally. Some mites are hematophagous, meaning they require blood to complete part of their life cycle, typically for egg production. However, the vast majority of mite species do not feed on blood. This biological distinction determines which species pose a health concern to humans and pets.
Not All Mites Are Blood Feeders
The order Acarina, which encompasses both mites and ticks, displays a wide array of feeding habits. Most mites are free-living and play ecological roles as scavengers, decomposers, or predators of other small invertebrates. House dust mites (\(Dermatophagoides\) spp.) are common indoor species that feed exclusively on organic debris, such as shed human and animal skin flakes (dander).
Other species cause irritation without consuming blood directly. Scabies mites (\(Sarcoptes\) \(scabiei\)) are parasitic, burrowing into the outer layers of the skin and feeding on tissue and secretions rather than piercing a blood vessel. Similarly, chigger mites (larval Trombiculidae) attach to a host and inject digestive enzymes that break down skin cells. They consume these broken-down cells as a liquid, but they are not true blood-suckers.
True hematophagy involves specialized mouthparts designed to pierce the host’s skin and directly access capillary blood. For these species, blood is an obligatory requirement, often necessary for the female to lay eggs. This need for a blood meal is what drives the mites that become accidental human parasites.
Identifying Hematophagous Mite Species
The mites that actively suck blood and most frequently affect humans or pets are typically external parasites of other animals. These species only bite humans when their primary host is unavailable, usually due to the host leaving or dying. A major group is the Bird Mites, which includes the Northern Fowl Mite (\(Ornithonyssus\) \(sylviarum\)) and the Chicken Mite (\(Dermanyssus\) \(gallinae\)).
These mites primarily infest birds like pigeons, sparrows, and chickens, living in nests and roosting areas. The Chicken Mite is a nocturnal feeder, hiding in crevices near the nest during the day and emerging at night for a blood meal. When a bird nest near or inside a structure is abandoned, the mites migrate indoors in search of a new host, leading to human bites.
Another significant group is the Rodent Mites, such as the Tropical Rat Mite (\(Ornithonyssus\) \(bacoti\)) and the House Mouse Mite (\(Liponyssoides\) \(sanguineus\)). These mites are external parasites of rats and mice, and their life cycle can be completed rapidly, sometimes in as little as 10 to 12 days. Like bird mites, they seek human hosts when the rodent population is eliminated or dies off, driving the mites into living spaces.
Rodent mites are extremely small, often described as the size of a period in 12-point font, making them difficult to spot. They prefer warm areas like spaces around pipes or furnaces where their rodent hosts often nest. Identifying the exact mite species often requires finding the source of the infestation. This source is usually a bird nest in an attic or eave, or a rodent nest within the walls.
Health Risks and Symptoms of Mite Bites
Bites from hematophagous mites typically result in localized skin reactions and significant discomfort. The most common symptom is intense itching, which can develop quickly after the bite. This reaction is due to the host’s response to the mite’s saliva, which is injected during feeding to prevent blood clotting.
The physical manifestation of the bite often appears as small, red bumps or raised papules on the skin. These lesions frequently resemble mosquito bites but can be more persistent and numerous. Bites are often concentrated on the torso and limbs, especially in areas where clothing is tight or the skin is thin.
The severe itching often leads to excessive scratching, which is the main source of secondary health complications. Breaking the skin barrier allows common skin bacteria to enter, resulting in painful secondary bacterial infections that may require antibiotic treatment. The nocturnal feeding habits of some species can also cause disrupted sleep patterns, leading to fatigue and anxiety.
While the most common blood-feeding mites rarely transmit infectious diseases to humans in the United States, their bites indicate a nearby pest infestation that needs to be addressed. The psychological distress and physical discomfort from persistent, unexplained bites are a significant health impact. The solution to stopping the bites is always to eliminate the primary host—the birds or rodents—and clean the nesting material.