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. Even 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 exotic tick (Aponomma komodoense), which feeds exclusively 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 mouth-parts to pierce their hosts' skin and extract blood. These mouth-parts 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, needle-like hypostome
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 cement-like 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.
How do ticks breathe?
Like many arthropods, ticks breathe air through tiny openings along their body called "spiracles." Ticks are famous for surviving periods underwater because they have a reduced need for oxygen compared to other creatures. A tick breathes between one and 15 times an hour.
The reason solutions such as alcohol and nail polish work in removing ticks is because they are irritants, not because the tick becomes suffocated. Despite their effectiveness, it is not recommended to use these products in the removal of ticks due to the chance that the arthropod regurgitates its saliva and gut contents into the bloodstream of the host. This can increase the risk of disease.