The tropical rat mite,
Ornithonyssus bacoti, is occasionally a problem. Usually, this comes about when rats abandon
their nests, or when they are killed as part of a rat eradication program.
Mites associated with the nests then move into human dwellings looking
for food. However, rat mites will attack humans when their preferred host
- the rat - is not available. Usually rats confine themselves to the structure
of the building and the rat mites can make their way in through very small
cracks in the walls and into the home, especially if a nest behind the
wall have been abandoned and the mites find themselves hungry.
Mites are red if they have obtained a blood meal but unfed rat mites are
a light cream color. They are also very small but visible to the naked
eye (provided you have good eyesight). They are about the size of a period
at the end of a sentence. When engorged, females are about 1/25th inch
(1 mm) long, a size that can be seen with the naked eye. You can monitor
for them by using clear sticky tape and applying it in areas where you
suspect they are accumulating. Rat mite like warm areas. They tend to
accumulate in walls, especially if there is a heat source, for example,
bathroom walls, kitchen walls where plumbing pipes run, these areas have
warm water running through and humidity. The rats like to nest in these
areas which makes it easy for the mites to penetrate the wall into areas
where humans are in the evenings (because the mites are primarily nocturnal).
Most complaints involve the customer waking up with very itchy bites primarily
on their torso. Stomach, waist, sides of the body and sometimes around
the scalp and hair line. Generally, the homeowner has picked up the mites
in the bathroom when going through their evening rituals before going
to bed. Mites are heat seekers and will get on the homeowner and be carried
to bed with them. During the night, the mite will bite repeatedly and
since they inject an anticoagulant saliva, the bites won't itch for
a while (sometimes hours later).
The rat mite has a life span of about 63 days. Mites (like ticks), only
feed when they are breeding or molting. Rat Mites hatch from an egg and
look similar to the adult but need to grow and mature before they are
able to breed. As they grow they need to cast off their "skin"
(exoskeleton) to accommodate their new larger size. Each time they molt,
they need a blood meal and they also need a blood meal each time they
are preparing to lay eggs. Rat mites can go several weeks between meals.