No.1 Arista apparently bare or pubescent?

At this blog, I'll publish articles about useful tips for identifying tachinids.

Also, I'll write casual articles about trivial everyday matters.

This one is the former.

Here I'll introduce the following topic as an essential trait for identifying tachinids: "Arista bare or pubescent?"

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NO.1

Arista bare or pubescent ?

　　　Importance：　★★★★★

　　　　 Difficulty：　very easy

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Firstly, what is an "arista"?

The photo below will help you understand its meaning! An "arista" is a thread-like sensory organ that arises from the 3rd antennal segment (=1st fllageromere)．

Thus, "Arista bare or pubescent?" refers to whether or not there're hairs on this part．Since the arista itself looks somewhat like a hair, it may sound weird to you. But, you'll get used to this concept once you see actual specimens!

⚫︎Case: "Arista apparently bare"

Let's take a look at the photo below. There seems to be no hairs on arista, which places it in the category of "arista apparently bare."

Then, how about the next one?

At first glance, it appears to have no hairs on arista as well. But, take a closer look! You can now tell that there're so short, if hardly visible, hairs on arista. Then, does it fall into the category of "Arista pubescent"?

Actually, this one also belongs to the "Arista apparently bare" group. Let's look back the first question: "Arista apparently bare or pubescent?" The one with no clear long hairs should be assigned to "Arista apparently bare."

Then, where is the boundary?

How short must the hairs be for us to say it's nearly bare? Isn't it the matter of our subjectivity?

Actually, I think individuals with ambiguous traits are rare.

But, fortunately, there's a clear definition of the boundary. It's below.

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Length of the longest hair of arista ≦ The basal width of arista

　　　　　　　　　　　　　　　　　　　・・・ arista apparently bare

Length of the longest hair of arista ＞ The basal width of arista

　　　　　　　　　　　　　　　　　　　・・・ arista pubescent

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for reference...

⚫︎Case: "Arista pubescent"

It is as plain as day that there're many hairs on the arista. The hairs are clearly wider than the basal width of arista. Particularly, this individual has such long and dense hairs that we often explain it as plumose.

The length of hairs on arista varies much from species to species. So, when the arista is pubescent, the ratio of the longest hair length to the basal width of the arista is often shown on descriptive papers, and this value is definitely an important key for identification.

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Among Calliphoridae and Sarcophagidae, probably the majority of species have pubescent aristae. In the case of Tachinidae, however, species with apparently bare aristae outnumber the counterpart.

Though that does not mean that species with pubescent aristae are rare. Common genera, such as Dexiosoma, Prosena, Thelaira, and Trigonospila, posess pubescent aristae. Especially, subfamily Dexiinae contains many tachinidae species with pubescent aristae.

So, what do you think of the first journey into a key trait of Tachinidae? We've explored the feature: "Arista apparently bare or pubescent ?"

Thank you for reading.