Robber Fly

Robber fly dining on a Silver Spotted Skipper.

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Robber Fly

Robber Fly (Ommatius ouachitensis)

All Robber Flies (Family Asilidae) are predators. They capture prey and inject neurotoxins to immobilize. After also injecting digestive enzymes, they suck out the liquidized innards of their prey, leaving little remaining except for an exoskeleton.

Members of genus Ommatius are easily identified because they are the only North American species with feathery antennae, although these are difficult to see without binoculars or in a photo. You can see the fuzzy moth-like branching of the antennae in the enlarged versions of these photos.

Species identication within this genus is much more difficult, especially for females like the one I photographed, because Ommatius is currently separated into species by characteristics of the male genitalia. On his website, Norm Lavers does note that black on the hind femur takes up more than 25% of the length in O. ouachitensis. The ID I received for this specimen on BugGuide was tentative as are most of the other IDs I found online. Therefore, I will say that this Robber Fly is definitely a member of genus Ommatius and probably an O. ouachitensis.

I photographed this specimen during the late afternoon in a small clearing behind our garden. Becoming most active as dusk approaches seems typical for this species. They perch in open locations waiting to ambush a passing insect. Typical perches are bare twigs, fence wire or, in this particular case, the straw in my mug of water. I've found O. ouachitensis relatively easy to photograph because they tend to remain perched and are not easily disturbed. I've even watched through my camera's viewfinder as one of these Robber Flies suddenly left and then returned to the same location with an insect a second or so later.

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Robber Fly (Ommatius ouachitensis)

ABC Wednesday: R is for Robber Flies

ABC Wednesday: R is for Robber Flies
(in this case two male Efferia aestuans)

Robber Flies are in an insect family (Asilidae) where the question "Care to join me for lunch?" should never be answered in the affirmative.

Adult robber flies capture their prey on the wing. Just about any flying insect from leafhoppers to dragonflies to other robber flies is fair game. I have seen robber flies bring down insects two and three times their own size. Large prey they simply ride down to the ground. Small prey they will fly with to a feeding location of their choice. Robber flies stab prey with their sharp beaks and then inject a mixture of neurotoxins (for a quick kill) and digestive enzymes. They then suck out the partially pre-digested body juices of their victims.

Sources and links:
Cirrus Images
Herschel Raney's Random Natural Acts
Norman Lavers Robber Flies of Crowley's Ridge
BugGuide Efferia Page

Thanks to Mrs. Nesbitt's Place for hosting ABC Wednesday.

ABC Wednesday: R is for Robber Flies

Another Robber Fly

Robber Fly (Genus Ommatius)

Perched on a bare twig, a pose typical of males of this genus. The definitive genus characteristic is that all members of Ommatius have antennae that are slightly branched (feathered) like those of a moth, a feature that's close to impossible to see while in the field, but can be seen in one of the photos on Herschel Raney's Ommatius page. Feathered antennae among robber flies are unique to this genus.

Another Robber Fly

Robber Fly

Robber Fly (Taracticus octopunctatus)

Thanks to Herschel Raney for IDing this specimen that showed up under our porch light. Like all other members of Family Asilidae, this little robber fly is a predator.

Robber Fly

Robber Fly

Robber Fly (Triorla interrupta)

Triorla interrupta is one of the more common species of robber flies around here. This female has taken down a grasshopper that's too large for her to fly with, but she isn't about to abandon a juicy meal just because some fool with a camera is taking her picture. Grasshoppers seem to be T. interrupta's preferred food when its in open, grassy areas where hoppers abound, but this species is aggressive and will take on just about anything smaller than a bird. Herschel Raney has some shots of T. interrupta feasting on everything from dragonflies to a large horsefly. That's not too shabby for a robber fly that's slightly built and only about 7/8" long.

Robber Fly