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.

Mini Robber Flies

I cut a couple of medium sized Black Walnut trees that were growing on the edge of a small prairie patch beside the house.  The trunks were about four inches in diameter, so after stripping off the branches, I left them in the lawn beside the barn to cut up for firewood.  When I returned from adding the branches to the brush pile, I found the logs being used as a perch and hunting platform by a swarm of small Robber Flies.

Robber Flies come in all sizes, but it’s usually the large species that get all of the notice.  Being extremely tiny doesn’t keep these guys from being quite attractive and interesting.  Sunlight on the transparent wings produced a shifting pattern of pastel purple, blue and green.

These are predators that feed on other small insects.  Each log had dozens of flies taking advantage of the slight elevation above the lawn grasses to watch for passing prey items.  When you’re that small it doesn’t take much of a rise to put you well above the action.

Prey of the day appeared to be small leaf hoppers.  The hoppers were so small that I couldn’t even see them in the air.  The Robber Flies with their super sized eyes had no such trouble.  Each quick trip out from the log resulted in another capture.

A variety of leaf hopper species were being captured.  Unfortunately, I couldn’t identify them with any more accuracy than I could the Robber Flies. 

I watched the Robber Fly action for quite a while.  The flies would eat the select portion of the leaf hoppers and then drop the remains before heading out for another capture.  I didn’t want to disturb the action, so I left the logs where they lay.  I’ll finish cutting them up some other day.

Some Insect Fliers

Last year I saw an extra abundance of Robber Flies. These large, hairy predators lined the walking paths, waiting to dart out and seize some small flying prey. So far this year, they’ve been rather scarce. This mating pair is working hard to see that the population increases.

Crane flies are beginning to become more abundant. This one was acting even more ungraceful than your average Crane Fly and landed on this leaf after falling off the one above. Judging by the light color, I’m going to attribute its bumbling flight to the possibility that it just recently emerged as an adult.

Giant Swallowtail butterflies are having a super year. I’ve been seeing three or four at a time around the Monarda patch. Unfortunately, I have yet to get a shot of one of these gorgeous creatures that’s in focus. They keep their wings in constant motion and tend to hover rather than settle on the flower. As abundant as they are now, I should have several opportunities to get that elusive focused shot.

Bee Flies are great. They look threatening, but don’t bite or even bother to investigate humans. Many have coloration along the wing veins that makes them more attractive than a lot of the small, brown skippers. In fact, they often resemble butterflies when seen perched on a flower, their primary food source. The larvae are parasitic, but fortunately for us, they parasitize insects.

Well, it’s not flying yet, but it will be before long. This Monarch caterpillar is at rest beneath a milkweed leaf. Signs of feeding were quite evident at the top of the plant. It wasn’t until I got my face almost to the ground that I could see what had been doing the feeding. Despite the abundance of milkweeds at Blue Jay Barrens, I rarely see Monarch caterpillars. It’s always a joy when I do.