The tropical rat mite is almost too small to be seen, but can inflict an astonishing amount of pain and misery.
This nearly microscopic member of the tick and spider family is neither tropical nor exclusive to rodents. Although rats are its preferred host, any mammal can provide a meal for this rapacious pest. Despite the fact that Ornithonyssus bacoti is reportedly one of the most common house-invading species, there is surprisingly little information about it.
A New York Magazine article by Jessica Roy from 2014 describes them as being worse than bedbugs. “Why are rat mites so much more disgusting than bedbugs?” she wrote. “Because they come from RATS. Do I even need to explain how disgusting rats are?”
Residents of the Santa Monica Mountains don’t have to deal with New York City rats, but they may have an elevated risk of encountering tropical rat mites this year. The wet winter and abundant food has resulted in a bumper crop of rodents, increasing the odds that rat mites are also abundant this season.
Common rat mite hosts include the tree rat and the native dusky-footed woodrat, or pack rat. O. bacoti reportedly must feed on rat blood in order to reproduce but that doesn’t stop it from snacking on the nearest mammal, if its rat host dies or abandons its nest.
According Los Angeles County Vector Control, “mites can become serious pests when there are many rats living within the structure, but most often they make their presence known shortly after control measures are started to eliminate the rats (the primary host). When trapped or poisoned rats die or fail to return to the nest, the mites migrate into the living areas of the structure to feed on human or animal hosts.”
Unfortunately for humans, the mites are attracted to carbon dioxide and heat and can travel long distances at a remarkably rapid rate for something so small.
Vector Control reports that “the mites are ultimately drawn to those areas within the home which experience the greatest amount of human activity. Rooms such as kitchens, family rooms, bedrooms and work areas maintain the highest concentrations of carbon dioxide and are highly attractive to the mites. Mites are also attracted to frequently used furniture such as sofas, recliners and beds, and will bite the occupants as they rest or sleep.”
Two other related mite species also occasionally cause problems for humans and pets: O. bursa, the tropical fowl mite; and O. sylviarum, the northern fowl mite. Both of these species are associated with both domestic and wild birds but can also be found in homes, attracted by wild birds nesting around the house or by a backyard chicken coop.
Bites of all three species can reportedly be painful, even if the biter is too small to be seen, and can result in an itchy dermatitis and mosquito bite-like welts. Cats and dogs may be hardest hit by an infestation. In particular, rat mites seem to seek out cats. Symptoms may include fur loss and a red rash on the belly or tail area.
Although there are topical treatments for the skin irritation for humans and animals, and many vets prescribe systemic anti-mite medications for infested pets, research indicates that the only effective way of eliminating an infestation is getting rid of the rodents and their nesting material, and making sure future rodents are excluded from the home by sealing entrances like gaps around pipes and vents. Do not use rodenticides!
Vector Control also points out that “trapping or otherwise killing rats may increase the activity of the mites as they search for other hosts,” leaving victims in a quandary. Mites are sometimes visible when they are on the move. A fine-toothed comb can be used to remove them from pets. For humans, bites can be treated with Cortizone cream, lidocaine sprays, or calamine lotion. A vet should be consulted when pets are affected.
Frequent vacuuming, dusting and washing may help control mites. Some mite survivors swear by diatomaceous earth, others by spraying vinegar or rubbing alcohol on bedding and hard surfaces, others claim nothing works. Sometimes the victims simply have to wait out the infestation, once the rats are eliminated and excluded.
Vector Control points out that the mites do not burrow beneath the skin, and that they are “easily removed by bathing or showering.” They are not known to transmit any disease, and since neither rat mites nor bird mites can reproduce in the absence of their primary host, they will eventually die out; all of which may be a least a small comfort to anyone coping with a full-scale invasion.
More information on tropical rat mites and their fowl (and foul) relations can be found at: www.publichealth.lacounty.gov.