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Tick back designs meaning

I was hoping you would tell me if the different designs on the back of ticks have any meaning (ie: male or female, type of tick) or are they just random decoration? Thank you.

Shirley, Santa Barbara - May 7, 2021

Curator Response

Dear Shirley,

While the markings on a tick's back are not 100% reliable for identification, they are often a strong indication of the species and, in some cases, even the sex of the tick. There are about 50 species of ticks known from California, and it is often no simple feat to identify them, since most are only reliably distinguished based on microscopic structural features. As luck would have it, though, the ones you sent happen to be fairly distinctive. I'm fairly sure these are the male and female of the American Dog Tick, Dermacentor variabilis.

When we're dealing with adult ticks—not larvae or nymphs, the two successive immature stages—the way to tell a male from a female is pretty easy: males have a scutum (the plate on the back) that almost covers the entire body. The female's scutum is much smaller and bib-shaped, covering only about a third of the body, and since the scutum doesn't change size, it covers even less of the body when the female tick is engorged with blood! Nymphs are trickier, since they all have a small scutum like the adult female, but the total body size of a nymph is smaller than the adult size. Larvae are smaller still and have only six legs as opposed to eight in the nymph and adult.

Now, to finally answer your question, the markings you noted are indeed indicative of the female and male of Dermacentor variabilis! That's the female on the left with the small pale scutum and almost cross-shaped dark markings, and that's the male on the right with the long, pale zig-zag markings. There is some variability within this species, but most individuals will look similar to these.

Last note: it shouldn't be left unsaid that this species is a known vector of Rocky Mountain spotted fever, though rarely so in California. Unless they've been feeding on you for at least 6 hours, though, this is not a concern.

Stay curious,

Schlinger Foundation Chair and Curator of Entomology Matthew L. Gimmel, Ph.D.