The Robber Flies of Crowley's Ridge, Arkansas

An Illustrated Field Guide by Norman Lavers

Asilidae : Laphriinae

Species of Crowley's Ridge

The third subfamily is the Laphriinae, a very large and charming group with eighteen species on Crowley's Ridge. These include nine species in the Genus Laphria, large wonderful mimics of bumble bees, and very popular among entomologists. But some of the other genera are quite tiny. All have in common that they lay their eggs in rotting wood, thus providing their larvae with a rich source of beetle grubs.



Atomosia puella

For an example of a tiny one, this one here is Atomosia puella and is probably 6-7 mm long, the males even smaller. For the first year that we studied the robber flies, we never noticed them. Then when we learned that they existed, we found they were one of the most abundant species around, and in fact were numerous in our own garden!


They are like tiny little dots, but once you get your eye in for them, you see them sitting head down on the walls of the house, on tree trunks, telephone poles, or on pieces of wood on the ground (especially, in our garden, on the wood frames of our raised beds). Note the black abdomen with the thin white bands. But they are so small, even with your close-focusing binoculars you won't see them as clearly as in this enlarged photograph.


This is more what they will look like to you. Nevertheless you can identify them from some distance by their thin elongate form and their alert head-down posture on almost any wooden, usually vertical surface. Often you will see them fly up to chase prey, then return to the same spot.


If you have a light-colored house you will easily see them on the walls, often several together. In this picture, the larger one, above, feeding on a fly, is a female, the smaller one below is a male.


You won't have to watch very long before you see the male doing his courtship "hover" an inch or two in front of the female's face.


Here is a female's eye-view shot of the courtship flight.


On their tiny scale, they are very efficient predators, almost constantly holding prey, and give you an indication of just how many tiny flies, aphids, flying ants or termites, there are in the air every minute. Atomosia puella come out early in May and fly till about the end of July.



[back to the top]


Atomosia melanopogon

This very similar fly is Atomosia melanopogon. The previous species had all black legs with just the smallest touch of pale yellow at the base of the tibiae. On this one you will see the very tips of the femora are chestnut, and a third or usually much more of the tibiae are chestnut. The extent of chestnut is fairly evident, especially if you get a picture of it. Additionally, the white bands on the abdomen are much less evident. This is a female, with a white face; the male has a black face, another feature which might be visible.


If you can get it in a photograph, there is a positive identification feature here: Look at the veins on the wing that extends beyond the tip of the abdomen. In the center you see two veins close together, nearly parallel, but as they go away from you they come to a point just before the margin of the wing. (Click this up to full size to see it easily.) That technical feature marks this as A. melanopogon. The similar A. puella has these two veins going parallel clear to the end of the wing, without ever meeting.


We find A. melanopogon landed on the bare ground on eroded loess soil on the edges of abandoned quarries or similar open rather barren places.



[back to the top]


Atomosia rufipes

This is Atomosia rufipes. It differs from A. puella by having yellow, instead of black legs. But to separate it from the next very similar species, note the hind tibia has a small but very evident bit of black at the apical end, and also has three segments of the hind tarsi black. You would probably need to take a photograph to see these tiny details. Scarbrough (1972), the first person to study robber flies on Crowley's Ridge, recorded them in a garden in Monette, Craighead County, just a little bit to the east outside the range of our territory, so the species should be looked for. I took this picture elsewhere in Arkansas; I have never seen the species here.



[back to the top]


Atomosia sayii

Finally, here is Atomosia sayii. It differs from the preceding two species by having completely yellow legs, with only the final tips of the tarsi black. (But virtually every Atomosia you see on Crowley's Ridge will be the dark-legged A. puella.) Herschel Raney in Faulkner County, in the center of Arkansas, has these on the walls of his house alongside A. puella. But I have only found A. sayii, on Crowley's Ridge, on stands of ragweed next to crop fields. Reportedly, it lands on leaves or twig tips among or beside fields of cotton or soybeans.



[back to the top]


Cerotainia macrocera

Here is Cerotainia macrocera, another tiny dot. This one sits on the tips of twigs, as many of the tiny dots do. It is separated from dots in other genera by its very long antennae which can be seen even from a distance, if they are against a contrasting background. I had two pictures of this species in the section "What is a Robber Fly?" showing the general characteristics of robber flies. This very common species (once you learn how to spot it) flies from June to the middle of August.



[back to the top]


Cerotainia albipilosa

There are two species of Cerotainia on Crowley's Ridge. The second, much less common, species is Cerotainia albipilosa. They can look very similar. Often the thorax on both species can appear bare and shiny black. But if you get C. albipilosa in the right angle of light, you will see they are more or less covered with white hairs.


The white hairs are not always easy to see, which can make this species difficult to separate from C. macrocera. On this one the camera flash has brought out the white hairs (otherwise not visible) on the thorax. But on most C. albipilosa, you can at least see the white between the eyes, whereas C. macrocera is yellow-brown between the eyes. Look at the next picture, of C. macrocera, to see this.


If you can make them out at all, the sparse body hairs on C. macrocera are golden in color., rather than white.



[back to the top]


Orthogonis stygia

Here is our real specialty on Crowley's Ridge, Orthogonis stygia. Known from a handful of individuals found in scattered south-eastern states, it is the only New World member of this genus. Other members are found in Australasia and Madagascar, and, I believe, Japan, a typical relict distribution. O. stygia was described fifty years ago on the basis of half a dozen females. Since that time, only one more female had been found, and never any males. It was considered one of the rarest Robber Flies in the country until we discovered that the species was rather common in steep shady ravines throughout the length of Crowley's Ridge (See discussion in Taber, 2003). Our pictures, so far as I know, are the only pictures ever taken of the species in life, and the males that we have found the only ones known to science (Barnes et al., 2007). The species flies during the month of July, is about 2.5 cm long, and is a Pompilid wasp mimic. There is a look-alike species in Arkansas, Pogonosoma dorsatum, but so far I have never found it on Crowley's Ridge. If it does one day turn up, Orthogonis stygia can readily be identified by its distinctive behavior.


I said earlier that most Robber Flies lay their eggs in the ground. The Laphriinae, however, lay their eggs in decaying wood, another excellent hunting ground for beetle larvae. The male Orthogonis stygia takes possession of a large decaying oak log, usually on a dark shady canyonside, and guards it against all comers while waiting for a female to come by to such a choice oviposition site. As can be seen from the aggressive posture of this individual, they even protect the log against intruding entomologists. No matter how many times I chase them away in my efforts to photograph them, when I turn around they have come right back. They often greet me when I arrive at their log by doing a mimic wasp threat display, hanging in front of my face buzzing loudly. The lookalike robber fly, Pogonosoma dorsatum, takes possession, not of decaying oak, but decaying pine logs, and is so shy it is gone the moment you arrive.


Another caution, however: A large shiny black Mydas Fly (a Robber Fly relation) is out at the same time as Orthogonis, in the same habitat, is similarly a Pompilid wasp mimic, and is similarly territorial over big rotting logs, and will even fly out and buzz you aggressively as you approach. But if you look carefully, you will see the first segment of the abdomen on the Mydas Fly is red, and the Mydas Fly has rather long, clubbed antennae.



[back to the top]


Lampria bicolor

This is Lampria bicolor. It is not difficult to identify, with its tomato-red abdomen, once you convince yourself it is a robber fly and not a wasp. Note the pointy knobs on the lower side of the hind femur, a recognition sign for Lampria.


The genus is much more common in the tropics. I find L. bicolor, on Crowley's Ridge, in low shrubby vegetation.



[back to the top]


Lampria rubriventris

Another beautiful species in this genus, Lampria rubriventris, differs from the preceding by having red front tibiae, instead of the forelegs being totally black as in L. bicolor. I myself have not seen this species on Crowley's Ridge, but a specimen collected in St. Francis County is in the Arthropod Museum of the University of Arkansas. In other parts of Arkansas I have found this species in weedy fields.



[back to the top]


Laphria flavicollis

We now start on the Genus Laphria proper, mainly bumble bee mimics. Here is Laphria flavicollis. It is a medium-sized robber (some individuals are quite small) all black except for the yellow mystax and the very furry yellow thorax. There is some yellow hair on the legs. The abdomen is bare and shiny black. With the genus Laphria, the pattern of black and yellow is key to identification.


With the exception of the strange Nicocles pictus (which by now is long gone) Laphria flavicollis is usually the first Robber Fly out in the year, appearing in the first week of April, and marks the real beginning of the Robber Fly season. This fly is a denizen of the tall poison ivy beds which make up much of the under-story of closed canopy hardwoods on the richer soils of Crowley's Ridge, landing in the middle of the broad leaves. In early spring, when I am eager for the Robber Fly season to begin, I watch the bare poison ivy vines, and the moment the new leaves fully unfurl, L. flavicollis appears. This species has the habit, when disturbed, of flying 8-10 feet away and then landing facing you, in the posture of this one. Almost all of the Laphria species are woodland robbers, appearing in spring and early summer, and the place to find most of them is sitting on a poison ivy leaf. Most of the Laphria on Crowley's Ridge lay their eggs in decaying hardwoods.


Laphria as a group have a stiff beak specially designed to pierce the armor of beetles, on which they feed by preference, but at the time flavicollis appears, crane flies are the most abundant insects around.


In this and the next remarkable pictures by Cheryl, a Laphria flavicollis can be seen ovipositing in a rotten Sweetgum (Liquidamber styracyflua) log. In this picture the oviduct can be seen protruded into a crack in the log.


In this picture the red egg is actually visible in the oviduct as the egg is being attached to the wall of a beetle larva exit hole.


Two eggs are visible inside the hole.



[back to the top]


Laphria grossa

This is Laphria grossa. As the name implies, it is a large robber, the size of the biggest bumble bees, which it imitates quite well, the long black sheath for the beak somewhat spoiling the effect. On this species the mystax is yellow, the thorax is yellow, and most of the abdomen is yellow. Note especially the little fan of yellow hairs in front of the bright yellow haltere at the base of the hind leg. That will separate it from the next species. The main population of this species is east of the Mississippi River. The next species is found generally west of the Mississippi River.



[back to the top]


Laphria lata

It is harder to see—black against black—but here the little fan of hairs in front of the haltere is black, and this otherwise identical species is Laphria lata. The truth is, many authorities suspect these are both the same species, and it will probably take a DNA test to straighten things out. At any rate, both of these forms are present on Crowley's Ridge.


As it happens, here on the Ridge we seldom see Laphria lata in that black and yellow color morph. Almost always here it appears in a distinctive burnt orange and black pattern, as in this example of L. lata. These are huge bruisers. Look at the nail-like beak coming out of the sheath.



[back to the top]


Laphria macquarti

Here is Laphria macquarti, a medium to large-sized fly with yellow mystax, yellow thorax, and three (on the male) or four (on the female) abdominal segments yellow. What separates this from other species is that on this female, the central pair of legs have the tibiae covered with long yellow hairs.


The rather spectacular males have the fore and middle pairs of tibiae both with the long yellow hairs.


As with most Laphrias, the preferred prey is small beetles, which in some cases can really liven up the color scheme.



[back to the top]


Laphria thoracica

This is Laphria thoracica. It is a large, loud-buzzing, dramatic species with a black mystax, black abdomen, and black legs. The deep yellow pile on the thorax differs from that on other Laphria in the fact that it goes down the side of the thorax and curves around in front of the wings. The patches of orange hairs on the black legs are unique.


Even from a distance the black hairy head, bright yellow wrap-around thorax, and orange-haired legs, make L. thoracica instantly recognizable. This is a female. Males have more or less yellow on the abdomen.



[back to the top]


Laphria sicula

Not all the Laphria are bumble bee mimics. Some are smallish, slender, and perhaps more wasp- than bee-like. Indeed some authorities place these in a separate genus. This all-black robber is Laphria sicula. It is also common sitting on top of the poison ivy leaves side by side with L. flavicollis. It is quite small, black with a white mystax, white hairs on the legs, and a noticeably long slender beak.


In common with the other Laphria, L. sicula feeds mainly on small soft-bodied beetles. This individual L. sicula is afflicted with red mites.


Sometimes you can see L. siculas on top of a large well-rotted oak or other hardwood log, where they come to lay their eggs.


If you search carefully along the sides, you may find the empty pupal cases that have protruded out of beetle-larva holes for the adult fly to emerge.


Robber Fly pupae have characteristic features, the thorny face, the rows of short thorns, sometimes larger and smaller ones alternating, on the abdominal segments. Evidently these abdominal thorns help to obtain purchase when the pupa (more technically, the puparium) is scrabbling its way up to push into the open for the adult fly to emerge.



[back to the top]


Laphria index

Here is Laphria index, a very handsome member of the smaller, slimmer Laphria, black with a little triangle of golden on the back of the thorax, and then flattened, combed-out gold on the last few segments of the abdomen.



[back to the top]


Laphria cinerea

This is Laphria cinerea, a rather untypical slender black Laphria with tufts of grayish hair. The fat round shiny black hind femora will help identify it as a Laphria. Unlike all those I have described so far, this species lays its eggs in decaying pine wood. If you walk through a pine woods (not all that common on the essentially hardwood-forested Ridge), in an area with lots of rotting pine trunks lying on the ground from an old fire or blow-down, sometimes you will see what appears to be a large blow fly taking off from the center of a log, towering, and disappearing. If you come up very quietly on the next pine log, you may see this robber guarding his choice oviposition site from other males, so that he will have first pick of any females that come by. This robber is commoner, in Arkansas, in the Ouachita and Ozark mountains, and very scarce on the Ridge.



[back to the top]


Laphria affinis

Here is the final Laphria species on the Ridge, once more a bumble bee mimic, but the most untypical of its genus. It is Laphria affinis. The specimen picture will show that the pattern is black mystax, yellow thorax, shiny black abdomen, and then all six legs thick with long yellow hairs. The male of this species, as with L. cinerea, guards a rotting pine log, as that is where the females go to lay their eggs. What is totally different about this species is, they come out at the end of September and their flight period extends probably to December, reversing the spring and early summer flight period of virtually every other Laphria species.


So if you see a Laphria in September or later it will be this species. (Caution: See, below, Mallophora orcina, an unrelated bumble bee mimic, which comes out in the summer.) The male L. affinis are almost always sitting in the middle of a well decayed pine log, waiting for a female to appear. When a female does appear, the male flies up and grabs her, and mating commences in midair within two seconds.


The males will sometimes come up close on their log, and face you just like Orthogonis stygia, and even fly at your head in a wasp- or bee-like warning, but it is rather timid (they usually fly around to the back of your head), and they will quickly fly off, perhaps to land face down about eight feet up on the trunk of a living pine tree.


When the males leave her alone, the female Laphria affinis will find a part of the rotted pine log that the bark has slipped off of and push the tip of her abdomen into a small hole or crack to deposit her eggs.



[back to the top]