In many families, a thorough search for ticks is part of any hike, camping trip or other journey into the woods. For people who live in rural areas, particularly those who work outdoors, looking for ticks is often a part of daily life. It's easy to think of these tiny arachnids as something to watch out for in relatively wild terrain, but ticks don't confine themselves to the wilderness. They're adaptive and resilient, and you can find them in distinctly urban areas, like the parks of New York City.
The typical response to finding a tick is often disgust. It's partly because ticks are parasites -- they feed on their hosts' blood. Although people see them most often on themselves and their pets, ticks also attack wild animals, farm animals, birds and reptiles. On top of that, some ticks, particularly females, swell dramatically when they ingest a lot of blood. An engorged tick, or one that's full of blood, can have a bizarre, even grotesque appearance.
In addition to their feeding behavior and appearance, ticks are disease vectors. They can carry illnesses from one animal to another. In fact, ticks are the primary disease vector in domestic animals. In terms of human illness, only one parasite spreads more illness -- the mosquito. Ticks can spread a wide variety of disease-causing organisms, including bacteria, viruses and protozoa.
Ticks themselves are just as diverse as the diseases they carry. They live all over the world, and there are as many as 850 total species, divided roughly into two categories -- hard and soft. A hard tick has a shield-like plate called a scutum that covers part of its back. If you look at a hard tick from top down, you can also see its capitulum, which looks like a head. Soft ticks, on the other hand, don't have a scutum, and the only parts of it you can see when you look at it from above are its back and legs.
Regardless of whether they're hard or soft, all species of ticks have a few things in common. Everything about them, from their swollen appearance to their ability to spread disease, comes from their need for blood. In this article, we'll explore how ticks retrieve blood from their human hosts, as well as how they live, travel and reproduce.
Many people group ticks into the same category as fleas and mosquitoes -- insects that suck blood. However, ticks are really arachnids. Adult insects have three pairs of legs, and their bodies are made up of three segments: the head, the thorax and the abdomen. Arachnids, on the other hand, have four pairs of legs. Spiders are also arachnids, but ticks aren't spiders. Spiders' bodies have two segments, the cephalothorax and the abdomen, while ticks' bodies aren't segmented in any way.
A tick's body is small and relatively flat, so it's easy for it to attach itself to a host and eat its fill before the host notices. This is particularly true for immature ticks, which can be smaller than the period at the end of a sentence. Hungry adult ticks are often smaller than sesame seeds. Some ticks have also adapted to blend in to their hosts' bodies. One example is the Aponomma komodoense, which feeds only on komodo dragons and is almost indistinguishable from a komodo dragon's scale. Many ticks have to stay in place for a day or more to finish a meal, so the ability to go unnoticed is central to its survival.
Adult ticks have eight legs, each of which is covered in short, spiny hairs and has a tiny claw at the end. These spines and claws have two main purposes. They help ticks grasp blades of grass, leaves, branches and other vegetation. They also allow ticks to grasp their hosts.
Ticks use their mouthparts to pierce their hosts' skin and extract blood. These mouthparts can vary from species to species, but in general, from the outside to the inside, a tick's mouth includes:
- Two palps, which move out of the way during feeding and don't pierce the host's skin
- Two chelicerae, which cut through the host's skin
- One barbed, needlelike hypostome
Hard and soft ticks both have these mouthparts, although you can only see them on a soft tick if you look at its underside.
The barbs on the hypostome are like the barbs on a fishhook. They point back toward the tick, making it difficult to remove the tick without damaging the skin. Some ticks secrete a cementlike substance with their saliva, which dissolves when the tick is ready to drop off of its host. This substance can make it even harder to remove the feeding tick. The saliva also keeps the host's blood from clotting while the tick eats. But unlike a flea's saliva, it doesn't usually include compounds that cause itching and swelling.
As a tick eats, its body, or idiosoma, expands, although the amount of expansion varies. The scutum of a male hard tick covers much of its back, so its body can't stretch to hold a lot of blood. Soft ticks don't have scutums to get in the way of feeding, but they don't require an immense store of blood to lay eggs, so they don't swell as much as hard ticks do. Female hard ticks swell immensely as they store the blood they need to lay their eggs.
Next, we'll look at ticks' life cycles in more detail, and we'll explore the differences in feeding patterns between hard and soft ticks.
At its most basic, a tick is a parasitic blood pump. Like all parasites, it feeds off of its host without giving the host anything in return. A tick's body has numerous adaptations that allow it to find hosts and ingest their blood.
Tick Life Cycles
You probably have a clear idea of what happens to a person or an animal if it doesn't get food -- it starves to death. Ticks can also starve to death, but often the process takes months or even years. However, without food, ticks can't do much. Ticks are a clear illustration of how food works as an energy source. Ticks need energy from blood in order to grow, develop and lay eggs. Without blood, ticks can't do any of this.
A tick begins its life as an egg. When the egg hatches, a six-legged larva emerges. Aside from its missing set of legs, the larva looks a lot like an adult tick. Its first host is usually a small mammal or a lizard, and it has to find a host in order to grow. After feeding, the larva drops to the ground to digest its food and begin to grow. After one to three weeks, the larva molts and becomes a nymph.
A tick nymph has eight legs and looks like a smaller version of an adult tick. It has to find another meal, usually from another small mammal, bird or lizard, before it can molt again. Once the nymph is finished eating, it drops to the ground to continue its development. Some species of soft tick molt several times, consuming a blood meal before each molt. After its final molt, the tick is an adult.
An adult tick has one job -- to reproduce. In hard ticks, the female tick attaches to a host and feeds, often for more than 24 hours, before mating. The male tick feeds before mating as well, but he's often a fraction of the size of the engorged female when mating takes place. Often, the male dies after mating, and the female dies after laying anywhere from 2,000 to 18,000 eggs. Soft ticks are an exception. Many species of soft tick eat several smaller blood meals and lay eggs several times. This is one reason soft ticks don't consume as much blood in one sitting or swell to the extent that hard ticks do.
Hard and soft ticks also have different methods for finding hosts, which we'll examine in the next section.
Hard and soft ticks differ in how they behave and find food. Soft ticks generally live in animals' nests and burrows. Females lay their eggs in their host's nest. Larvae, nymphs and adults crawl through the nest to find hosts. They usually feed at night, and they don't spend much time attached to a host. While hard ticks may spend days consuming a host's blood, soft ticks often finish a meal in about the time it takes a flea to do the same task.
Hard ticks, on the other hand, find food through a behavior known as questing. A questing tick positions itself on a blade of grass, a leaf or other vegetation. It stretches its clawed limbs outward and waits for hosts to pass by. Ticks can't jump or drop down onto their hosts -- when a host brushes against a questing tick, the tick simply hangs on. In many tick species, larvae quest at ground level. Nymphs climb a little higher into vegetation to find slightly bigger hosts. Adults climb highest of all in their attempt to find large animals to use as hosts.
Questing often involves a lot of waiting, and it may seem like such a haphazard method wouldn't be very successful. But ticks use several signals to decide when and where to quest. Many tick species have eyes and can detect color and movement. Hard and soft ticks can detect carbon dioxide (CO2) that animals produce as they exhale. By following these signs, ticks have a good chance of finding hosts.
Some species of hard ticks don't spend much time questing. They find a host as larvae and stay on that host for their whole lives. These are known as one-host ticks. A few species are two-host ticks. They mature from larvae to nymphs on one host, then find a second, larger host as adults. Most hard tick species are three-host ticks, which feed and drop to the ground at each stage of their lives.
Since ticks rely on blood for food, they have the potential to transmit diseases from one host to the next. Let's take a look at some of the diseases ticks can carry and how doctors can treat them.
Ticks and Diseases
A freshly hatched tick might be free from disease, but as soon as it takes a meal from an infected animal, it becomes a potential disease vector. In fact, ticks can carry more diseases than any other arthropod in the world. Their efficiency at spreading infection comes from the way they feed. Many tick species feed on at least three hosts before they die. If one host is sick, the tick can carry the infection to the others. Hard ticks also have to keep their mouthparts embedded in their hosts' skin for hours or even days before they finish a meal. This gives pathogens plenty of time to make their way into the host.
Here's an overview of how a tick typically becomes a disease vector:
- When the tick finds its next host, it inserts its mouthparts into the host's skin and begins to suck the host's blood. The tick's saliva travels into the wound to keep the blood from clotting. The saliva carries infectious material into the wound. If squeezed during grooming or during an attempt to remove it, the tick may regurgitate infected blood back into the wound.
- The infected host becomes a new disease reservoir for other ticks.
The diseases ticks transmit vary from place to place. This is because different animals and their species-specific diseases thrive in different parts of the world. But that doesn't stop tick-borne illnesses from spreading outside of a particular geographical area. A good example is Rocky Mountain spotted fever, the first disease positively identified as having a tick vector. As its name implies, Rocky Mountain spotted fever started out in the Rocky Mountain area of the United States. Migrating animals have carried ticks and bacteria to other parts of the United States. Today, the disease has spread to much of the Southern, Central and Eastern United States.
Like Rocky Mountain spotted fever, many of the other diseases ticks can spread to people are rickettsial illnesses. These are caused by bacteria in the Rickettsiae family. A wide variety of tick-borne rickettsial exist in different parts of the world. Some are:
- Queensland tick typhus and Finlanders Island spotted fever, which exist in Australia
- Ehrlichiosis, which is more common in some parts of the United States than Rocky Mountain spotted fever
Many rickettsial illnesses are spotted fevers that cause rashes, nausea, vomiting, headache and fatigue. Most of the time, these illnesses respond to antibiotics, but some can be fatal without prompt medical treatment.
Black-legged ticks, also known as deer ticks, can carry a bacterial infection called Lyme disease. Lyme disease exists in Europe, Africa, Asia and much of the United States. It causes a red bull's-eye rash, fever, headache, a stiff neck and muscle pain. Ticks can also transmit the malarialike illness babesiosis, which comes from protozoa. Some tick-borne illnesses are dangerous only to animals, such as swine fever, which infects pigs, and canine prioplasmosis, which infects dogs.
Removing a tick promptly is vital to preventing many of these diseases. Next, we'll review the right way to remove a tick.
In general, hard ticks take a long time to transmit diseases to people. Some diseases require the tick to be attached for four or more hours. Most Lyme disease infections occur after an infected tick has been attached to its host for more than a day. For this reason, it's important to inspect yourself and your family members for ticks regularly any time you're somewhere ticks are likely to live, including:
- Tall grass
- Dense shrubbery
- Wooded areas
Since tick larvae often wait for hosts at ground level, it's also a good idea to check for them after sitting on the ground. You should also keep an eye out for ticks after bagging leaves or carrying wood.
Since it generally takes four hours for a tick to make you sick, it's a good idea to check for ticks every two to three hours. Pay special attention behind the ears, anywhere that skin folds and all over the scalp. Keep an eye out for tiny tick nymphs -- nymphs frequently transmit Lyme disease because they're small and hard to notice.
Most of the time, it's also easier to remove ticks before they've spent a lot of time on your body. The longer the tick stays attached, the more swollen its abdomen will be, and the harder it will be to grasp the tick without squeezing it. In addition, the tick's cementlike saliva hardens as the tick feeds, making it harder to remove.
When you find a tick, here's what to do:
- Use a pair of tweezers to grasp the tick where it attaches to the skin. If you spend lots of time in tick-prone areas, it's a good idea to keep one set of tweezers on hand solely for removing ticks. Always disinfect them afterward.
- Pull the tick straight out. Pull slowly and firmly, and do not jerk or twist the tick. Be careful not to squeeze the tick's abdomen.
- Wash the area thoroughly with soap and water.
- If possible, save the tick. It may help doctors make a more accurate diagnosis in case of illness.
If you've heard any old wives' tales about how to remove ticks, chances are they're not a good idea. Applying rubbing alcohol, petroleum jelly, nail polish remover or a lit match will not help you to remove the tick. It's more likely to cause the tick to regurgitate, spreading potentially infective material into the bite.
Although removing ticks promptly can significantly reduce your chances of getting sick, a better strategy is to keep from being bitten at all. Next, we'll look at how to prevent tick bites and control tick populations.
Tick Prevention and Control
If you're going into an area that's likely to be infested with ticks, there are several simple steps you can take to reduce your chances of being bitten. Here's a rundown:
- Wear light-colored clothing. This makes it easier to see ticks crawling on your clothes. A good trick for removing ticks crawling on clothing is to pick them up with a loop of tape.
- Wear long sleeves, and tuck your pants into your socks or boots.
- Wear a hat.
- If you're working in the yard, wear work gloves.
- Spray your clothing with an insect repellent containing DEET. Avoid spraying your skin, since long-term DEET exposure can lead to reactions like hives and blisters. Follow the label instructions carefully, and don't rely on the repellent to completely prevent tick exposure. Some ticks will crawl over areas sprayed with repellents until they reach a person's skin.
Ticks can make animals sick, too, so it's a good idea to keep ticks away from your pets:
- Keep pets indoors when possible, and inspect outdoor pets for ticks regularly.
- Following directions carefully, treat your pets with an insecticide or repellent that targets ticks. Some flea treatments work on ticks as well.
- Clean kennels and crates thoroughly, paying attention to cracks and crevices where ticks may lay their eggs.
You can get a good idea of whether you have an infestation on your property by dragging a white, rough-textured cloth through areas that might be prone to ticks. If the cloth collects lots of ticks, you have an infestation. A good rule of thumb is that the neater your yard appears, the less likely it is to be infested with ticks. Ticks like to live in overgrown weeds, leaf litter and decaying wood, so it's good to clean up any such areas in your yard.
If you discover an infestation, it's a good idea to treat your home, your property and your pet at the same time. However, treating your entire lawn with a pesticide may do more harm than good. Ticks generally live in tall grass, weeds and shrubs, so they don't spend much time in mown grass. If you're treating your property with a pesticide, focus on shrubs and overgrown areas you can't reach with a lawn mower. Any time you're using a pesticide, follow the label instructions to the letter.
Getting rid of ticks can take a little persistence. If commercial tick-control products don't do the trick, contact your local exterminator for assistance. To learn more about ticks, fleas and other related topics, check out the links on the next page.
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More Great Links
- Anderson, Renee R. and Laura C. Harrington. "Tick Biology for the Homeowner." Cornell Cooperative Extension. (8/13/2007) http://www.entomology.cornell.edu/MedEnt/TickBioFS/TickBioFS.html
- Borreliosis & Associated Disease Awareness UK. "About Ticks." (8/13/2007) http://www.bada-uk.org/videointro.html
- Centers for Disease Control. "Southern Tick-associated Rash Illness." (8/13/2007) http://www.cdc.gov/ncidod/dvbid/stari/index.htm
- Doggett, Stephen L. "Spotted Fevers." University of Sydney and Westmeade Hospital. (8/13/2007) http://medent.usyd.edu.au/fact/spotfev.htm
- Harvard University. "Ticks of New England: Fact Sheet and Gallery. 2006. (8/13/2007) http://www.uos.harvard.edu/ehs/pes_ticks.shtml
- Hill, Catherine and John MacDonald. "Ticks." Purdue University. (8/13/2007) http://www.entm.purdue.edu/publichealth/insects/tick.html
- Illinois Department of Public Health. "Common Ticks." (8/13/2007) http://www.idph.state.il.us/envhealth/pccommonticks.htm
- Jacobs, Steve. "Entomological Notes: Four Common Ticks of Pennsylvania." (8/13/2007) http://www.ento.psu.edu/extension/factsheets/common_ticks.htm
- Kohler, P. G. and F. M. Oi. "Ticks." University of Florida IFAS Extension. (8/13/2007) http://edis.ifas.ufl.edu/IG088
- New York City Department of Health and Mental Hygiene. "Ticks." (8/13/2007) http://www.nyc.gov/html/doh/html/ehs/ehstick.shtml
- Potter, Michael F. "Ticks and Disease: Answers to Often Asked Questions." University of Kentucky. (8/13/2007) http://www.ca.uky.edu/entomology/entfacts/ef618.asp
- Ruedisuli, Frank L. and Brigitte Manship. "Tick Anatomy." Tick Identification key. (8/13/2007) http://webpages.lincoln.ac.uk/fruedisueli/FR-webpages/parasitology/Ticks/TIK/tick-key/tick_anatomy.htm
- TickTexas. "Anatomy of Hard and Soft Ticks." (8/13/2007) http://www.ticktexas.org/ticks/ticks101_anatomy.htm
- University of Sydney and Westmeade Hospital. "Ticks." (8/13/2007) http://medent.usyd.edu.au/fact/ticks.htm
- Vredevoe, Larisa. "Background Information on the Biology of Ticks." University of California. Davis. (8/13/2007) http://entomology.ucdavis.edu/faculty/rbkimsey/tickbio.html