#common eastern physocephala

[onenicebugperday]

@berrypeacherine submitted: Hi! Found this friend in my house (eastern PA, in May) and relocated it outdoors. I tried IDing it, but haven't figured it out. It looked very wasp-like, but kept its wings out like that. Probably about 18mm / 3/4" long. All black, except for pale yellow around the eyes. Is it a wasp after all, or some kind of fly? Thank you!

Hello! With antennae like that, definitely a fly. It's a common eastern physocephala, Physocephala tibialis. That's a type of thick-headed fly in the family Conopidae. Their larvae are parasitoids of bees, but adults feed on nectar :)

[jonnysinsectcatalogue]

Common Eastern Physocephala - Physocephala tibialis

With Potter Wasps finally introduced to the blog, we can also explore these curious Flies of the garden that were stumbled onto this year. These strange looking insects were drawn to the yard’s oregano and also seem to like perching on rose leaves as well. Akin to Hoverflies, these insects mimic other stinging Hymenopterans in order to avoid becoming someone’s dinner. The insects mimicked in this case are Potter Wasps which are a handy family to mimic since Wasps are likely to retaliate if disturbed. If the mimicry holds, the false warning allows this specie to enjoy flowers at their leisure. However, this specie of Fly is not a Hoverfly, and belongs to another Fly family altogether! To tell the two apart, this Fly has a long proboscis jutting from its face which it uses to slurp up nectar from the plants it visits. Hoverflies lack this proboscis; they lap up nectar with a spongy-mouthpart (this video here provides a great example of this feeding). This Fly belongs to a somewhat elusive family called Conopidae (Thick-Headed Flies). It’s an odd name considering the individuals photographed in this post, but that’s the family they were sorted into. 

While they share some behavior with insects like Hoverflies and Bee Flies, these insects have their own habits and traits. Firstly, a fun example of their habits is the piling behavior shown in Pictures 4, 6 and 8. It’s not necessarily that there is a mating pair going on, they might just be piling on each other for kicks. Unlike more common Flies, males and females of this specie aren’t distinguished by their eye placement. Instead, watch for the abdomen position and the structure of the abdomens to confirm a mating pair. Since the individuals on display here have rounded abdomens, it’s likely that we are seeing two males in a pile (which can get as tall as 3 or even 4 individuals). Why do they pile? Who knows, but it’s an odd behavior! Interestingly, there doesn’t seem to be much struggling or infighting during the process. I can only speculate, but it may be a vigilance behavior or somehow involve mate selection. While we know now what males look like, look for the abdomen to have a claw-shaped tip (curving downward) to identify a female. Such a clawed tip is for more than just for show, and we’ll dive into that behavior on the next posting of these Flies. It’s very important that gardeners keep an eye out on these Wasp-mimics in order to protect their Bees...

Pictures were taken on July 21, 28 and August 20, 2020 with a Google Pixel 4.

[jonnysinsectcatalogue]

Common Eastern Physocephala - Physocephala tibialis

This post involves descriptions of parasitoid behavior with Bees as this insect's primary host. If you are squeamish regarding Bee parasitism, I recommend clicking on this random link to see another post from the blog. Otherwise, I offer the following information regarding this seemingly innocuously specie of mimicking Fly:

Before following up from an earlier post, here's a small refresher. This insect is a Thick-Headed Fly of the family Conopidae. They rely on mimicry of Potter Wasps and Thread-Waisted Wasps to dissuade predators from eating them, as otherwise they are defenseless flower-loving Flies. While they appear to have a sharp bayonet protruding from their face, this is actually a proboscis which they use to sip nectar. Alongside the nutritional value that flowers can provide, Conopid Flies value flowers for another reason: they attract pollinators which the females need in order to lay their eggs. In an earlier post, I highlighted that it is essential to know the differences between male and female Psychocephala Flies if they appear in your garden in substantial amounts. The male Flies have a blunted abdomen, while female Flies have an abdominal tip structured like a crushing claw. You can see an example of this claw-like structure in Picture 9. This "claw" is a combination of a structure called a theca and an extension to the abdomen's 7th segment. Despite the position along the abdomen, these structures are not used for mating and it cannot fold on itself to crush.

Now since it looks so menacing, what does that "claw" actually do? In a manner similar to a crowbar or prying tool, this Fly specie uses this claw to open a Bee's abdominal exoskeletal plates in order to jab an egg inside the Bee itself. Yes, you read that correctly. Moreover, this process can be done midflight or while a Bee is investigating a flower! If the prying is successful, a Fly larva will begin to parasitize the Bee host as soon as it hatches and develop within its body. If the immune system doesn't neutralize the laid egg, the growing larva can change the behaviors of the Bee for its own benefit for up to 2 weeks. The larva presumably does this using chemical secretions or similar mechanisms (this phenomenon is not well understood and lacks lab documentation). It breaks my heart to type it out, but this behavioral change can all finalize with the parasite directing to host Bee to bury itself in the ground in order to create a secure environment for its pupation. It's not just Bees are afflicted by this form of parasitism. Just as there are many branches in the Conopid Fly family, there are many hosts that can be pried open. While disturbing, this is just the life cycle of one of the many creatures in the circle of life. The best we as humans can do is monitor the Bees and stay vigilant for this parasitic pollinator.

Pictures were taken on July 30 & August 20, 2020 and July 15 & 21, 2021 with a Google Pixel 4.