JULY
2002

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

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!

 

Writer: Tom Turpin
Editor: Olivia Maddox