Robber Flies

I took this series of photos one afternoon about six months ago during a time when I was experiencing internet connectivity problems.  The file has been stuck in my blog folder since then, along with several others.  I deleted the others, but I am such a fan of Robber Flies that I just had to make this post.  Resting on a leaf about half way down into the canopy of an herbaceous border sits this Diogmites species. 

Robber Flies are predators.  They spend much of their time sitting where they can watch for passing flying insects. I enjoy watching this species because its head is so mobile. It swivels its head in the direction of even the slightest bit of movement, which at some point always includes the photographer.

This slightly larger member of the Robber Fly group is a representative of the genus Efferia.  It came to rest on my hand while I was working in the field, which I hope does not give anyone the impression that I move so slowly while working that animals find me a convenient perch.  The end of the abdomen tapers down into an almost sword like appendage. Although it looks to be a formidable weapon, it is used as a tool for laying eggs deep into flower heads or other locations deemed suitable for growth of the larvae.

This is Promachus hinei.  Although it’s not the most common in terms of total Robber Fly numbers at Blue Jay Barrens, it is the most commonly encountered species of Robber Fly. Because of their large size and noisy flight, they are hard to miss when you happen upon them in the field. On this particular day, almost every individual I found was busily feeding, and several were feeding on somewhat unusual items like this paper wasp. When hunting, Robber Flies launch from a perch, grab an insect from the air, and return to a perch to consume their prey. The Robber Fly’s first action after a catch is to insert its piercing mouthparts into the body of the captured insect and inject a chemical relaxant that attacks the nerves and calms the prey. Along with the nerve agent is an enzyme that liquefies the internal body of the insect, so the robber fly can drink its meal.

To some, this may look like a love embrace. Unfortunately, that fly giving the big hug is not moving in for a friendly cuddle. 

These big flies will take any prey they can handle, even if it’s their own species.  That’s a male of the species making a meal of a female.  You can see his piercing mouthparts just below his front leg in a direct line with the grass stem beside his head. I hope next summer is another bumper season for Robber Flies.

Robber Flies

 Blue Jay Barrens had its first frost of 2014 on the morning of September 23.  This is a full month earlier than last year.  Only the most susceptible of creatures showed any signs of damage, but it’s an indication that most of the marvelous insects will soon be disappearing.  While doing some work near the barn, I had this big Robber Fly use the bed of my wheelbarrow as a hunting perch.

 This is a female Promachus hinei, a species that is quite abundant here during late summer.  Robber Flies are predators that sit and wait for suitable prey to fly by.  When a likely victim, such as a smaller sized flying insect, is spotted, the Robber Fly darts out and snatches it from the air.

 Like most flies, the Robber Flies spend a lot of time on personal grooming.  Even while combing its abdominal hair, the fly is alert for potential meals.

 The capture is quicker than my camera.  The Robber Fly is just a loud buzz and a blur as it grabs a passing insect.

 Usually, the predator will bring the catch back to the same resting spot for consumption.  The fly inserts its tube-like mouth into the prey and begins to drink.

 

 The presence of four wings identifies the victim as a small bee.  Feeding appears to occur rapidly, because this fly ate three of these bees in just a few minutes.  It’s also possible that the fly just can’t resist a fresh kill and discards the previous catch before it is totally drained.  I love watching these big flies hunt.

 Later in the day, I found this medium sized Robber Fly.  This is a species of Diogmites and it tended to perch down low in the vegetation.

 It also frequently changed its hunting perch.

 When it spotted something moving in the air, it quickly turned its head in that direction.

 If the object of interest remained in view, the fly would realign its body with the head.  I think this guy made a catch, but it didn’t return to its perch and I failed to see where it ended up.

Soon after, I located this small robber fly from the genus Holcocephala.  This genus is commonly referred to as a Gnat-Ogre and it may actually have eyes bigger than its belly.  Gnat-Ogres perch on the tips of narrow leaves.  The wind was blowing this little guy around so much that I wondered how it could ever focus on a passing meal.  I’m going to enjoy the insects as much as I can before cold weather closes that particular avenue of pleasure.

Robber Fly Pestered by Flies

I’ve been seeing Robber Flies of all sizes, but my favorites are the big guys.  It’s enjoyable to watch something that is easy to approach and view without the use of any special optics.  These are ambush type predators that perch near an open area and fly out to capture insect prey as it flies by.  They always put on a good show.

I found this Promachus hinei busily consuming a large stink bug.  The Robber Fly inserts its mouth parts into its prey and then injects a calming toxin along with digestive chemicals.  The liquefied tissues are then ingested.

I’ve seen Robber Flies capture some rather large prey items.  The stink bug isn’t necessarily large, but it’s a heavy insect that probably took all of the Robber Fly’s strength to haul over to this leaf.

A swarm of small flies was taking advantage of this opportunity for a meal.  I’ve never before seen this type of behavior.  The flies arrived in a hurry, but I don’t know if they were attracted by the Robber Fly or the stink bug. 

Some of the little flies were using the Robber Fly as a perch.  The Robber Fly periodically raised its abdomen and kicked its legs to dislodge the little pests.  The scene reminded me of flies at a picnic.

The Robber Fly eventually completed its meal and dropped the bug carcass to the ground.  I found it interesting that none of the little flies followed the bug.  The bug only fell a few feet and if it was what originally attracted the flies, they should have been able to find it in its new location.  Maybe the pack followed the Robber Fly to take advantage of its next meal.  I’ll definitely be watching for these little flies on future Robber Fly kills.

A Camera Critters submission.