Copulating pair of Taeniaptera trivittata, a type of still-legged fly (Micropezidae). Males (or females, according to one source) apparently brush the eyes of the partner during mating, though this frame didn’t capture that. When flitting around leaves they wave their white-tipped forelegs and look just like small ichneumon wasps. They have thin waists but the pattern on their wings makes them look even thinner, waspier. Known to feed on rotting Typha, which was abundant nearby (John Heinz National Wildlife Refuge, Tinicum, PA).
If you come across a pair, please take a video so I can see the legs in action. I like to watch, and I know of others who are interested in this species.
I was photographing a spider a few days ago, and one frame that I was about to trash (jumping spider’s eyes not in focus) happened to show a kleptoparasitic fly that was drinking fluids from the captured ant. Because the fly is not especially visible I haven’t tried that hard to ID the fly (probably Milichiidae or Chloropidae), but I did find an interesting page showing a fly in Australia that was found near a salticid called an ant eater (Zenodorus orbiculatus).
If you have time to waste, here are some fun facts about kleptoparasitic flies:
Some species are attracted to volatiles released by captured prey (e.g., stink bugs). I have pics.
Some plants in the Apocynaceae seem to have evolved the ability to mimic the venom volatiles of paper wasps. The scent is attractive to kleptoparasitic flies because the wasps use the venom when they hunt (Heiduk et al. 2015). This is referred to as kleptomyiophily, apparently (new word for me).
Just in case you’re a fan of obscure diptera, I wanted to share some images of an insect I’d never seen before: Anthrax georgicus.
I initially identified it as Ogcodocera analis, which looks exactly alike to the untrained eye (like mine) but isn’t found in Pennsylvania. Anthrax georgicus parasitizes tiger beetles, apparently. The females lay eggs near the entrances to tiger beetle burrows and then the larvae attach to the beetle larvae and suck hemolymph. If you live near a place with dense population of tiger beetles, keep your eyes peeled for this fly. Or read about them here, in a fantastic post by Matt Pelikan. I gather they lay eggs by dive bombing.
The next photograph shows what it did in response to my flash.
I searched around to see if all flies do this, but couldn’t find anything about light-induced wing spreading. I did find an article by Andrei Sourakov on the startle response of a long-legged fly, again caused by a flash — they exhibit a tumbling escape behavior (see paper for pics). In a separate paper, Sourakov discusses the startle response of skippers (Hesperiidae) — again, I highly recommend taking a look at the figures so you can see the insects during their escape tumbles. In hindsight, I should have played around with flash sync speed to see if I could measure how quickly it could spread its wings. The shutter speed I was using was 1/200 second.
Just in case I’m completely wrong about the ID (which I based on this page) and you’re an expert with a moment to spare, I put a better view of a wing at the bottom. The posterior margin of the alula looks convex. I don’t have a better view of the antennae, unfortunately, which I know would be helpful for Bombyllidae. As a side note, insects that are jet black but have shiny white parts are a complete pain to photograph.