There are a handful of robber fly species in the United States that look like bumblebees. They are an impressive group. The best way to tell the difference is to count their wings. Robber flies (as with other flies) have two wings. Bumblebees (as with other bees) have four wings. Of course this isn’t the easiest thing to detect in living individuals. In the field, it’s usually best to look closely at the body. Robber flies are narrower and have a narrow mouth (like a little knife projecting from its head). Bumblebees are typically wider and their mouthparts are usually projecting in and out of flowers. Robber flies, on the other hand, don’t visit flowers – at least not to get pollen and nectar. They are usually looking for other insects to feed on.
I happened upon this male Laphria fernaldi a couple of weeks ago near Altamont, Utah (in Duchesne County). The area is a high desert sagebrush and willow habitat near Lake Fork Creek. This is without doubt one of the most beautiful flies in the US. Not only is it an impressive bee mimic, but the bumblebees that it resembles are those species with an orange or salmon colored spot on the abdomen – not your typical bee. It was kind enough to let me take a picture before it buzzed off.