Physocephala tibialis, Thick-Headed Fly

2013-12-29: Identified as Physocephala tibialis by Aaron Schusteff, Contributing Editor of BugGuide.

A few weeks ago, I tweeted:

2013-06-11 19:57: Found – or rather one of our cats did – an incredible wasp-mimic fly. Chilling in refrigerator for later identification.

2013-06-11 20:01: The fly looks very similar to /Physocephala/ except all-black at first glance. Will examine more closely later.

This is what she found:
Physocephala, Thick-headed Fly

Yes, that is a fly, not a wasp. You can tell it’s a fly from the antennae in the center of the face, instead of the top of the head, the large, rounded eyes that cover both sides of the face, instead of being restricted to the upper part of the head, and the “forked” feet.

For comparison, here’s the all-black Sphex pensylvanicus, Great Black Wasp, to which Physocephala bears, I think, a superficial resemblance. Note the position of the antennae, the location, size and shape of the eyes, and the clawed feet.
Sphex pensylvanicus, Great Black Wasp, on Pycnanthemum, Mountain-Mint

Even before I knew what it was, from past experience, I knew that wing venation would be important in identification. By chilling this individual in the refrigerator overnight, I got a few minutes of close-focus macro time to highlight all the key features. Based on comparing the wing venation to other examples on BugGuide, I think this is Physocephala, but I’ve submitted it to their experts for positive ID.

Here are my other photos of this impressive mimic.
Physocephala, Thick-headed Fly
Physocephala, Thick-headed Fly
Physocephala, Thick-headed Fly
Physocephala, Thick-headed Fly

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Flickr photo set



Trichopoda pennipes, Feather-legged Fly

Trichopoda pennipes, Feather-legged Fly, on Pycnanthemum, Mountain-Mint, in my garden yesterday. Although it’s widespread and common, occurring throughout North America, this was the first time I’ve noticed this species in my garden.
Trichopoda pennipes, Feather-legged Fly, on Pycnanthemum, Mountain-Mint
This photo shows several of the keys to identifying this species:

  • “Feathered” fringes on the hindlegs, true of Trichopoda.
  • Orange abdomen. Females have a black-tipped abdomen. Males, such as this one, have a completely orange abdomen. 
  • Wings are completely black. This species has a transparent margin to the wing.

Trichopoda is a parasitoid of Hempitera, true bugs, including many agricultural and garden pests, such as squash bugs and stinkbugs. For this reason, it’s considered a “beneficial” insect:

Each female fly lays on average 100 eggs, which are placed singly on the body of a large nymph or adult bug. Most of the small, white or gray, oval eggs are placed on the underside of the thorax or abdomen, but they can occur on almost any part of the bug. Many eggs may be laid on the same host, but only one larva will survive in each bug. The young larva that hatches from the egg bores directly into the host body. The maggot feeds on the body fluids of the host for about two weeks, during which time it increases to a size almost equal to that of the body cavity of its host. When it has completed its development, the cream-colored third instar maggot emerges from the bug between the posterior abdominal segments. The bug dies after emergence of the fly, not from the parasitoid feeding, but from the mechanical injury to its body. The maggot pupates about an inch down in the soil in a dark reddish-brown puparium formed from the last larval skin, and an adult fly emerges about two weeks later. There can be three generations per year depending on location.

The fly overwinters as a second instar larva within the body of the overwintering host bug. Adult flies emerge in late spring or early summer. The only bugs large enough to parasitize at this time are overwintered adults. Subsequent generations develop on both nymphs and adults of the next generation.
Trichopodes pennipes, Parasitoid of True Bugs

Trichopoda pennipes, Feather-legged Fly, on Pycnanthemum, Mountain-Mint

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Flickr photo set: Trichopoda pennipes, Feather-Legged Fly


BugGuide: Trichopoda pennipes
University of Wisconsin-Madison, Department of Entomology, Midwest Biological Control News, Trichopodes pennipes, Parasitoid of True Bugs
North Carolina State University, Raleigh, Dept. of Entomology, Biological Control Information Center, Trichopoda pennipes