Mites are probably one of the most common insects on the earth and the vast majority of them have not been described yet. While the majority of them are harmless to humans and even helpful to us, there are several that are found in San Mateo County that can be a right nuisance. Most of these species are unable to invade your home without their host (usually rats or wild birds) but once there, they may bite humans if they reach a large population size or their host dies. Below are some of the most common biting mites in San Mateo County.
Tropical Rat Mites (Ornithonyssus bacoti)
The tropical rat mite is the most common mite that may invade your house and their bites can cause painful skin irritation that lasts for 2-3 days. It typically feeds on rats and only bites people living in rodent infested buildings, or just after a rodent infestation has been cleared. These mites do not live on their hosts and are usually found invading rat nests under houses and in cracks and crevices. While the mites can survive for many days without their hosts, they cannot sustain themselves on human blood and will usually die out once the rats have been removed. The best way to find these mites is to place sticky traps near areas you think may have rats living on or near them or in places near where you believe you are being bitten. As these mites feed at night, you will need to wait a minimum of 24 hours to know if you have these pests.
Chicken Mites (Dermanyssus gallinae)
Chicken mites are parasites of chickens and other wild birds and may infest attics and areas where birds have moved in and created nests. These mites do not live on their hosts and do not need to feed frequently which means they can survive for as long as 8 months without a blood meal. While the larval stage does not feed, the nymph and adult stages of this mite will routinely feed on blood preferring to search for their hosts at night. In order to find this mite, sticky traps must be set near cracks, nests or litter where birds have been and checked at least 24 hours after they have been set.
Northern Fowl Mite (Ornithonyssus sylviarum)
This mite lives on domestic and wild birds and is an important pest of poultry. Heavily infested birds will appear to have blackened feathers around the cloaca in the vent area and can lose 6% of their blood volume daily. These mites may become a pest to humans either when humans handle infested birds, or when wild birds that have been nesting in your home leave the nest or die, forcing the mites to seek a new host. Unlike the chicken mite, the northern fowl mite spends its entire life on its host and can only survive off the host for 2-3 weeks under ideal conditions (cooler temperatures and high humidity). These mites can be found by directly checking birds for signs of infestation.
Trombiculid mites (also called harvest mites or chiggers), unlike the other mites mentioned above, live outside in tall grass and plants where they feed on a wide variety of lizards, small mammals and birds. Only the larvae bite humans causing itchy red bumps that appear in 3-6 hours. Chiggers do not burrow into the skin and cannot survive on humans. Even if they were to get in your clothing, they would only live for 1-2 days. To keep yourself from being bitten while outside, wear loose-fitting long pants and long sleeved shirts and shower right away – scrubbing the skin to remove any chiggers that might be clinging to your skin. Avoid sitting on the ground or resting or leaning against areas with grass or plant matter, especially if there is evidence of wild rodents in the area. To find these mites, place 5-inch squares of black heavy duty paper or cardboard at the edge of grassy lawns in the sun for 5-10 minutes and check the surface for scurrying tiny red insects. To control and prevent chiggers from coming into your yard, use a mild (9-10%) permethrin spray once per week.
As always, if you believe you are being bitten by any of these mites, vector control is here to help. We offer rodent and bird inspections for your home and yard and can identify mystery insects for you. Please contact us at 650-344-8592 for assistance.