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.
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.
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 homeone 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 largea situation that occurs only rarely.