The Anatomy of a Tick

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Ticks are often mistaken for insects because they are bothersome parasites like fleas and mosquitoes. So in this lesson we'll look at the anatomy of a tick, explaining the different body parts to be familiar with.

What is a Tick?

If you're like me you hate the thought of ticks. These tiny blood-sucking parasites totally creep me out. One reason is because they often hitch a ride without you even noticing. Ticks are arachnids just like spiders and mites, though I feel badly for spiders that they have to share this relationship. And don't think that ticks are spiders just because they are arachnids - they most certainly are not. When I say ticks are small I'm not kidding. Some are so tiny that they may be no bigger than a sesame seed!

ticks of various sizes

Ticks are known for carrying diseases like Lyme, Rocky Mountain spotted fever, and anaplasmosis. There are 850 known species of ticks, and they are found around the world. They are more prevalent in warm, humid climates because the moisture in the air is necessary for their metamorphosis or transformation.

Tick Anatomy

Ticks have eight legs, three mouth parts, and no body segmentation.
Drawing of a tick, basic anatomy

Ticks may look like insects but there are distinct differences in their bodies that puts them in the arachnid family. First, is that they have four pairs of legs, so eight total. Insects only have six legs. Second, insects have three body segments, while ticks don't have any (spiders have two body segments). This special adaptation, along with being very flat, makes it much easier for ticks to latch on to you or another host without being seen. They also have spines on their legs, allowing them to get that grasp on you in the first place as you walk by.

There are actually two different kinds of ticks, hard and soft. The main difference between these two guys is that hard ticks have a scutum, which is a plate that covers its back like a shield. Soft ticks on the other hand do not have this plate.

Hard ticks, like on the left, have a plate covering their back. Soft ticks, like the one on the right, do not.
comparison of a soft and hard tick

Ticks' mouths have three parts. First are the two chelicerae, which the tick uses to cut through the skin of its host. Second is the hypostome, a barbed, needle-like structure that it uses to hold itself in the host while it has a nice meal. The barbs point backward which makes it difficult to pull the tick out. Finally, there are also two palps that simply move out of the way when the tick is eating. Together, all of these parts make up the capitulum, which looks an awful lot like a head.

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