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.

2015 Teasel Seed Head Collection

I have completed collecting Teasel seed heads for the 2015 season and am happy about the progress being made in reducing the number of Teasel growing in the fields.  Gathering the seed heads prevents the ripe seed from being scattered about the field and producing a new generation of this non-native invasive plant.

This is the third consecutive year that I have gathered Teasel tops from the seven acres of Teasel infested young prairie at Blue Jay Barrens.  This area, formerly the site of a moderate Teasel infestation, was practically Teasel free this year.

Most of the Teasel was scattered across the field as individual plants or small groups of two or three.  Areas of concentrated Teasel were generally less than 20 feet in diameter.

Unusual this year were the random plants that appeared to have lost their tops to browsing deer.

These topped plants managed to send up new shoots that flowered and produced seed heads.  The deer are going to have to do better than this if they wish to be heralded as a new weapon against Teasel.

My entire 2015 collection fit into three feed sacks, none of which was filled.  Total weight collected this year was 36 pounds, a 63 percent reduction over last year’s 97.5 pounds.  Teasel has a two year life cycle.  Year one is spent as a basal rosette of leaves.  During its second year, the plant sends up a tall stalk and produces flowers.  The plant then dies and the seeds are dropped as the plant dries.  The reduction in population size this year is a result of the 2013 seed crop being removed from the field.  The Teasel population size should continue to shrink, but the seeds previously dropped in the field can wait several years before germinating, so it will be a while before the population is reduced to a negligible amount.

I’ve had a lot going on the past couple of weeks, so the only time I could put to collecting Teasel was early in the morning.  Awaiting me each morning were a few Teasel heads, dew laden Indian Grass and a large collection of spider webs.

The webs were the product of the Banded Garden Spider, a common resident of this field.

Each orb web was accompanied by a structure of random webs to one side.  The spider was sandwiched between these two creations.  I assume the intent of the random webbing is to give the spider notice of the approach of a possible predator, such as a spider hunting wasp.

I left one late flowering Teasel head in place for a couple of days to give this Red-Banded Crab Spider a chance to finish its meal of Robber Fly.  That big fly should be more than enough to fill up the spider.

The buzz of Robber Flies was common throughout the field.  Diogmites species like this were especially abundant.

A first for me at Blue Jay Barrens was the sighting of this Citrine Forktail.  This tiny damselfly would be nearly impossible to find if you were searching for it.  I saw it only because the low angle of the sun made the insect appear as a bright fleck of gold among the sea of Indian Grass.  I don’t know what it was doing out in the middle of a dry prairie so far from water, but I’m glad it was there.

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.