Mite it bee the scutellum?

Last week, after I published the photo of a crab spider eating a honey bee, a reader wrote to say that the honey bee had a large Varroa mite on its thorax.

What he was seeing is not a Varroa mite but a part of the thorax called the scutellum. The honey bee thorax has several distinct parts but the scutellum is found just aft of the scutum. The scutum is the familiar part of the honey bee that helps us determine a bee’s age: older bees wear the hair off the scutum until it becomes a shiny, dark spot. We are also familiar with the scutum as a place to mark the queen.

Here you can see both the scutum (large anterior part of the thorax) and the scutellum (small posterior part of thorax). The two parts are connected by the scutellar grove.
Here you can see both the scutum (large anterior part of the thorax) and the scutellum (small posterior part of thorax). The two parts are connected by the scutellar grove.

The scutellum is adjacent to the scutum and is connected by a suture. The suture looks like a groove and is often called the scutellar grove, the dorsal groove, or the scutoscutellar groove. The scutellum rises higher than the scutum, a characteristic that is easiest to see from the side of the insect. The diagram of the honey bee thorax below shows the location of the scutellum.

Honey bee thorax (Snodgrass, 1956). The part labeled Scl2 is the scutellum.
Honey bee thorax (Snodgrass, 1956). The part labeled Scl2 is the scutellum.

Speaking of mites, however, the scutellar grove is home to a species of mite, Acarapis dorsalis, that is very similar to the tracheal mite, Acarapis woodi. The major difference between these two parasites is the place they call home—one prefers the trachea and the other is partial to the scutellar grove. A. dorsalis is generally not considered a problem for honey bees unless the populations grow excessively large—a situation that occurs only rarely.

Rusty
HoneyBeeSuite

Comments

Tom
Reply

Another superb photo!
I have been looking for crab spiders. No luck so far.

Tom

Nancy
Reply

Rusty,

I’ll e-mail you a picture: during hive check I have been quickly snapping images of each frame to enlarge and check for mites. (Trying to sugar dust diligently as soon as adults emerge.) I thought I had what seemed like a lot of mites. It’s good to know I could have been seeing the bees’ scutella, but then why is it not visible on a lot of bees? Obviously, if the spot is somewhere else, OK, that’s a mite.

2. What is the title of the Snodgrass book the diagram is from – I’d like the rest of the bee!

3. Did you ever get a recipe for the string treatment from the gentleman in NZ?

Thanks for the solid science!
Nan

Rusty
Reply

Nan,

1. I’m looking forward to the photo. The scutellum is difficult to see when a young bee is hairy; it is easier to see as the bee ages and the hair wears off. It is unusual to see many phoretic mites when brood production is in full swing. Phoretic mites are usually seen in the fall when there are not lots of brood cells for the mites to duck into.

2. “Anatomy of a Honey Bee” by R.E. Snodgrass is available from the internet archive at the Cornell University Library. It is free and can be downloaded in many formats, including .pdf and Kindle: http://archive.org/details/cu31924003168865.

3. No, good thought. I’ll try to find that.

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