A bee fly rests in a tidytips flower (Layia glandulosa) near Yucca, AZ on Thursday April 11, 2019.

What is this insect? A bee or a fly? The answer is that it is a fly that resembles a bee, and is hence a member of a large group called bee flies, family Bombyliidae, in the insect order Diptera, which includes flies and mosquitoes. The name “Diptera” means “two wings” and refers to the unifying trait of having one wing pair, not two pairs, which is what all of the bees and wasps they closely resemble have. So if there is ever any doubt about whether a bee-like insect is truly a bee, and you are able to count the wings and see two, then you have a bee fly. If you come up with four (two large forewings and two smaller hindwings), then it is a bee, wasp, or possibly a moth that mimics them; but in no case is it a fly. And if it is a bee fly, then it won’t harm you in any way despite the bee-like appearance, which probably helps protect the bee flies from would-be predators who might be discouraged by the perceived potential for a painful sting.

A wider-angle view of how I found the bee fly, resting just after sunset on a cool spring afternoon. The temperature drop probably reduced the bee fly’s metabolism to the point where it didn’t attempt to escape my camera lens.

Bee flies are a large, diverse, and often colorful group, but since they are seldom seen in urban, suburban, or heavily agricultural areas, they are much less well-known to people than they would be if people saw them more regularly. Even entomologists do not study this group as often as they study many others. As a consequence rather little is known about the exact biology of most species.

Another bee fly species rests in a different tidytips flower on the same plant as the other one just shown above.

What is known is that bee flies are usually parasites of true bees (order Hymenoptera) and other insects including beetles and grasshoppers. Bee fly females seek out the burrows or larvae of target insects and lay eggs in or on them. Some of the bee fly larvae will consume the brood or grubs of their prey, while others will simply cohabit within the nest and steal stored pollen or honey/nectar without actively feeding upon the other brood.

The similarities in overall body morphology is very evident between the two species of bee fly featured here.

Adult bee flies are expert and precise at hovering in mid-air, and are extremely agile, capable of changing flight directions radically in an instant. Their flight abilities are worth studying in greater depth in order to learn how they manage to pull off such tight and fast maneuvering with so little error, as it may have applications for human technology. Plus, it is simply very interesting!

Meanwhile, bee flies are often good pollinators of numerous wild plants, probably at least as effective if not more so than many true bees are to various plant species. They are most common in arid and semiarid habitats, which have the greatest diversity of different bee fly types, although there are representatives just about anywhere flowering plants occur. Both of these bee flies were photographed on Thursday April 11, 2019 near my house in Yucca, Arizona, resting in white tidy tips flowers (Layia glandulosa.)

I took this photo of a relatively large 15″ tall tidytips plant earlier in the afternoon while it was still sunny, and before I really paid attention to any insects visiting them. But even a casual snapshot illustrates that at least three bee flies of two species are visiting three separate flowers on the plant. Clearly the bee flies are seeking out pollen in the sparsely scattered tidytips plants, which are nowhere near the most common wildflower I have here at D:F Ranch.

The white tidytips (Layia glandulosa) is a Western US wildflower with a fairly large distributional range from Washington to Baja California and east to New Mexico, but is not necessarily common in most habitats. I only have a handful of scattered individuals appear every 2 or 3 years under decent fall and winter rainfall conditions to bloom in springtime here at 3000 feet in western Arizona. They do not emerge every year, so when they do it makes me happy to see the cheerful daisy-like pure white flowers with yellow centers. This appearance also gives it the common name of whitedaisy tidytips (both words often combined.) There are actually 12 species  in the genus Layia, and 10 of those are found only within the state of California, with L. glandulosa being the only one found widely outside of California. Including here at D:F Ranch in western Arizona.

Given the alarming decline of overall insect populations in certain habitats, it is pleasing to see a good diversity of different pollinators in my relatively undisturbed desert biome this spring. I hope that status will continue to be stable.