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7-11-02
Ticks,
Mites and Chiggers--Oh My!
What would the good ol' summertime be without ticks and chiggers? More
pleasant, that's what! Yes, ticks and chiggers are one of the associations
of summer that most of us could do without.
Ticks and mites belong to the group of animals known as arthropods. These
animals all have exoskeletons and jointed legs. The name arthropod literally
means jointed foot. Insects are arthropods. So are millipedes, centipedes,
crayfish, lobsters and pillbugs.
Along with spiders and scorpions, ticks and mites are classified as arachnids.
Arachnids do not have antennae or mandibles, as do the other groups of
arthropods. Most of the arachnids are predators, feeding on other arthropods,
such as insects.
However, ticks and mites are different. Some are exclusively plant feeders.
Spider mites, for example, are major plant pests. Others are parasites
on vertebrates, such as dogs, cats, deer and even humans. That is where
the rub comes in. Most humans prefer to not be a food item for another
animal.
How does this work? Ticks and mites have four stages to their lifecycle.
First is the egg. It hatches into the first of three mobile stages. This
is the larval stage, which has six legs, just like insects. The larva
molts into a nymph. The nymph has eight legs. The eight-legged nymph turns
into the adult, which also has eight legs.
All ticks are called obligate temporary ectoparasites. This means that
they have to feed on a host, but do so for a short period of time and
then drop off. Some ticks need only a single host. Others might need two
or more hosts to complete their lifecycle.
The deer tick has become well known because it is the vector of Lyme
disease, which is the most important vector-borne disease in the United
States. This tick first feeds on rodents of which the white-footed mouse
is a common host. As an adult, the main host is the white-tailed deer,
hence the name deer tick.
Another well-known tick is called the dog tick. This is the tick that
most humans encounter. As with the deer tick, the hosts for immature dog
ticks are rodents. The adults parasitize wild and domestic carnivores--our
dogs. This species is the vector of the disease known as Rocky Mountain
spotted fever.
So how do ticks find their hosts? Mostly, when they are ready to take
a blood meal, they crawl up on the top of plants and wait for a host to
brush against the plant. Once on the host, the tick searches for a grooming-free
site to start feeding. That is why most attached ticks on dogs are found
in the ears or between the shoulder blades. These are sites that the dog
cannot reach to remove the offending blood-sucking parasites!
Multiple host ticks, like the dog and deer ticks, generally remain on
the host for two to six days. That is enough time to acquire enough blood
to suit their needs.
Mites are much more numerous than ticks. There are around 800 species
of ticks, but some 29,000 species of mites. But mites also live as parasites
on warm-blooded animals, including humans.
One such pest mite is the chigger. These are larvae of trombiculid mites
and are also known as harvest bugs and scrub itch mites. They are difficult
to see since they are only about 0.25mm long, but when they get on you,
they produce a powerful itch. The normal hosts are rodents and birds.
The chigger lifecycle is much like the lifecycle of ticks. The newly
hatched larvae cluster on the tips of grasses waiting for animal hosts
to brush against the plant. When on the host, they then cluster inside
the ears of rodents and around the eyes of birds. On humans, the chiggers
are normally found where clothing is tight. Feeding takes several days,
after which the larvae drop off to continue their lifecycle.
How do you prevent becoming a meal for ticks or chiggers? Try to avoid
the type of habitat where these arachnids are waiting to pounce on the
next meal that walks by. Keep trousers tucked into socks, and use an insect
repellent. And, oh, yes, make sure that you do a personal tick check when
you get home. You can't be too sure that you haven't brought someone home
for dinner!
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