The Robber Flies of Crowley's Ridge, Arkansas

An Illustrated Field Guide by Norman Lavers

Other Insect Groups : Other Arkansas Robber Flies

Other Insect Species of Arkansas

In order to make this site more useful for people trying to identify robber flies in the state of Arkansas as a whole, I am going to begin including here, as an Appendix, some robber flies from other parts of the state that are unlikely ever to occur on Crowley's Ridge. I will begin here with a dozen or so, including some particularly attractive or dramatic species. By the time I have added another eight or ten (I will have to gain more knowledge and pictures), it will include every species anyone is likely to see in the state.

Apachekolos tenuipes

Here is an autumn-appearing member of the Leptogastrinae, Apachekolos tenuipes. This one is so distinctive it is easily identifiable through binoculars, and even perhaps with the bare eyes. It is on the large size for a leptogaster, about 15 mm, and entirely black, with hind legs that are long even for this long-legged group. It might be looked for in October in areas of tall bushy vegetation.

I am cheating here: I don't have a live shot of A. tenuipes. This is some other species of Apachekolos I photographed in Arizona. But they are all so much alike that in the field you can only separate them by geography. If it looks like this, but is in Arkansas, it is Apachekolos tenuipes.

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Leptogaster murina

This member of the Leptogastrinae is Leptogaster murina. It is best identified by habitat. It occurs in prairie remnants and open meadows of calf- or knee-high grass. Look for the tiny thread-like creatures moving low down in the grass, usually in places where the grass is a bit sparse, so that small patches of bare ground are showing through. They occur in colonies, so where you see one, you can probably find a few more. Through your binoculars they will appear plain brown, with unmarked yellow-brown legs. I find them in early summer in grassy prairies or meadows in the Ozark and Ouachita Mountains.

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Psilonyx annulatus

Here is Psilonyx annulatus. This particularly pretty member of the Leptogastrinae can be identified through binoculars by the bright orange ring on the hind femur, and the banded hind tibiae.

It occurs in small colonies in grassy areas in open damp woodlands, in the Ozarks and Ouachitas.

Here is a specimen picture of a pair of Pogonosoma dorsatum (the male above). I mentioned these in my discussion of Orthogonis stygia (which see) as lookalike species. Pogonosoma does not, so far as I know, occur on Crowley's Ridge, however Orthogonis stygia has recently (2008) been rediscovered in northwest Arkansas in a place where there are historical records, and it is quite possible that Orthogonis and Pogonosoma could occur together there. I have said Pogonosoma is much shyer in behavior. Additionally, it is found in association with rotting pine logs, not hardwoods (as with Orthogonis). Though they are very similar in size and appearance, Pogonosoma has white hairs on the legs (black in Orthogonis) and Pogonosoma has a much more up-turned beak (this is evident through binoculars), and more petiolate antennae.

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Laphria saffrana

Despite the death's-head pattern on the thorax, and the hornet-like coloring, this Laphria saffrana is much more charming than threatening. It is tame and even friendly appearing, landing on your boot-top or pant cuff to ride along with you as you are walking. It is identified by the fact that nothing else is remotely like it. Like all Laphriinae, it lays its eggs in wood, in this case rotting pine logs, and is found in open forests predominantly of pine trees. It is fairly common in the western part of the state.

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Laphria vorax

Laphria vorax is another handsome Laphriinid. This one is found exclusively in remnant prairies throughout the state. A bumblebee-mimicking Laphria out in the middle of a prairie grassland is sure to be this species (but always remember that the bumblebee-mimicking Mallophora orcina—which see—also occurs out in fields. Mallophora has little thread-like styles at the tips of its antennae, whereas Laphria antennae end in blunt paddles).

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Eudioctria tibialis

A member of the Stenopogoninae, Eudioctria tibialis is a tiny fly that looks like one of the twig-sitting dots, rather like Cerotainia without extra-long antennae. But a very important distinction is, it does not perch on twig-ends, but persistently lands on flat leaves at the top of small shrubs. I have found these in pine-oak woodland edge in the southwestern part of the state.

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Microstylum morosum

Here is the most dramatic robber fly in Arkansas, Microstylum morosum. At around two inches long, it is big for any insect, let alone a formidable predator. It is found in prairies, where it hunts grasshoppers by sweeping along close to the ground and chasing them into flight, where it quickly overtakes them. It has only been seen in the state a handful of times, all in southwestern Arkansas, at Terre Noire Prairie, at Grandview Prairie, at Okay Levee on Lake Millwood. It is unmistakable with its very long muscular body and its glowing green eyes. It seems to be out throughout the month of July. It will make any insect-hunter's day.

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Hadrokolos texanus

To go to another extreme, this Hadrokolos texanus vies with Townsendia nigra as the smallest robber fly in the state. This particular male is 3.3 mm long. It's a unique record for the state. We found it at the beginning of September. We were on the eastern shore of Lake Norfork when my sharp-eyed wife saw a tiny dot perched at the end of a twig fly out, then return to its perch. I caught it for that reason, but wasn't convinced it was a robber fly till I had it under the microscope. The identifying character here for Hadrokolos is that the male genitalia face forward.

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Lasiopogon oklahomensis

Lasiopogon oklahomensis is a member of the Stichopogoninae, and like the others in that group is a very small robber that is often found on or near to beaches. It seems to prefer beaches that are more rocky than sandy. It is so small it is difficult, even with close-up binoculars, to see the features (divided eyes, mystax, beak) that make you certain you are looking at a robber fly. To makes things more frustrating, the beaches are often covered with tiny flies with banded abdomens that look exactly like it. On the positive side, the males tend to sit in the middle of light-colored boulders, where they can be seen from some distance. They appear at the end of March and fly through May along the Buffalo and White Rivers in the Ozarks.

Here is the female. They seem to do very well catching small flies and winged termites.

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Holcocephala calva

Holcocephala calva, a twig-sitting dot, is very similar to Holcocephala fusca (which see), and is found in the same riparian habitats, but is a bit bigger, a bit longer in body, and the abdomen has a distinct hourglass shape, being pinched in in the central segments.

In this picture (slightly blurred because the wind was whipping the twig up and down) you can see the pinched in abdomen. I find these attractive little flies from July to November near or alongside streams in the Ozark Mountains.

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Megaphorus acrus

Though I of course deplore the non-scientific language, the word "cute" is often used to describe Megaphorus acrus. It is a very small bee mimic that is found in the vegetation or grassy areas on the high parts of sandy beaches alongside the Arkansas River.

When dozens are present, plus dozens of small fuzzy bees, it can really be a problem deciding which is which. A tip: unlike bees, the robbers never land on flowers. The size of the sand grains in this close-up picture will give you an idea of the size of this robber.

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Proctacanthus rufus

Proctacanthus rufus is an all-red Proctacanthus, looking exactly like P. hinei (which see). The external genitalia on the males differ enough in the two species that they are easily distinguishable through binoculars, but the females (as here) are not separable. They are best identified through habitat, P. hinei on bare sandy river beaches, P. rufus in slow-moving heavily vegetated marshy areas of streams.

However in places where the two species occur together, as at the bottom of Spring Creek Rd. on the beach of the Buffalo River, P. rufus has a more slender abdomen with small genitalia which are not broader than the abdomen. In addition, it has a brownish thorax with some patterning. Compare with the P. hinei in the next picture.

Proctacanthus hinei has a noticeably stouter abdomen, with noticeably prominent, somewhat upturned genitalia. The thorax, instead of being brownish, is distinctly reddish, and essentially unpatterned. These two pictures were taken nearly side by side.

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Machimus sadyates

Machimus sadyates is very much like Machimus virginicus (which see), except that instead of only having a narrow ring of orange at the base of the tibia, more than fifty percent of the tibia is orange.

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Machimus antimachus

Here is Machimus antimachus. It is a common species but confined to the western half of Arkansas, so I don't see it very often, and I am not very familiar with it. It seems to share a lot of features with Philonicus rufipennis (which see), particularly the long wings and the red or pale brown femora with usually a smudge of black on the outer side. It seems to be paler than Philonicus, with whiter sides and a fuller white mystax.

This female M. antimachus has redder legs, very much like Philonicus, but with the white sides to the thorax and full white mystax.

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