Why Care About Phorid Flies?

March 7, 2016

Phorid flies are 1 to 3 mm long insects that most people probably never see. They are busily at work in your backyard, decomposing, parasitizing, pollinating, and doing all the other things that small insects do. But people don’t care about them...how could they? They don’t even know they exist!

In the Urban Nature Research Center, I get comments all the time, or even looks from some of my colleagues that say “they are only flies”, or “there is more to the world than phorid flies”. Why, it is insinuated, can’t we just base conservation decisions on things people care about, like birds and mammals?

The problem with this idea is that birds and mammals are large, highly mobile creatures, like us. Although we tend to admire creatures that are most like us, in some ways they are the worst indicators for local conditions. After all, what tells you more about your backyard-a fly that never strays farther than one meter from the dead mushroom it was reared from, or the red tailed hawk that soars across half the basin in the afternoon? Small creatures give us information on a finer level than the large ones do.

Insects like phorid flies have faster generation times as well. That red tail may be five years old, but you know that fly hatched within the last year, and represents conditions that occurred this year only.

Finally, insects give us an incredible amount of knowledge because there are so many of them. In the book Insects of the L.A. Basin, Charles Hogue estimated that there were 2-to-3000 species of insects in Los Angeles. By studying phorid flies in detail, we know now that Charlie was way off. Here we can do the math: our study has found about 100 species of phorid flies in Los Angeles. Flies make up about 16% of the worlds insect biodiversity, and phorids make up about 1/40 fly species worldwide. We know that phorids are incredibly more diverse than one in 40, however, so let’s say one in 20 (.05). One hundred local species equals .05 of the 16% of insects that are Diptera, so 100 equals .05×16% of “x” (the total number of insect species). This calculates out to the staggering 12,500 species of insects in Los Angeles, most of which are probably not described! That means there are legions of tiny beetles, wasps, gall midges, and other unassuming creatures sharing our city, going about their business, maintaining the environment. It is our own private army of ecosystem service providers.

Oh, and by the way, phorid flies are incredibly cool.

All images by Kelsey Bailey.



(Posted by: Brian Brown)

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Ant-decapitating Fly Found in Glendale!

November 18, 2013

I just found out we have ant-decapitating flies here in Los Angeles! Dr. Brian Brown, the Museum's Curator of Entomology and one of the world's foremost experts on flies, made a chance discovery by looking right under the nose of an unsuspecting USC student.

It all started last Friday, while we were enjoying a nice stroll through the Nature Gardens. First, we checked out the Malaise trap that Brian and his staff set up as part of the BioSCAN project, which aims to survey the insect biodiversity here in Los Angeles. Then, we headed into the Nature Lab to see insects from this trap, and the 25 others that have been placed all over Los Angeles, being sorted.

As we got close to the demo table, Brian was suddenly transfixed. He'd seen something interesting on the screen that shows visitors the insects our scientists are sorting under the microscope. By some amazing coincidence, the USC student who was sorting a sample collected in Glendale, just happened to be looking at a phorid fly. Phorids, aka humpbacked flies, are the group of flies that Brian studies, and according to him, they are a mega-diverse family. How mega, you might ask? Apparently, there are estimated to be 40,000-50,000 species of phorid flies, and only 4,000 have been described by scientists so far. Wow!

But, it wasn't just any phorid fly. After taking a look through the microscope himself, Brian nonchalantly walks back over to me and said, "Yep, it's an ant decapitating fly."

Whoa, what? I had no idea we had ant-decapitating flies (ADFs) here in L.A.! How could he have neglected to mention this exciting fact during all of our insect musings? Sure he's regaled me with stories of ADFs from Costa Rica and Brazil, always with devilish decapitating detail. But, he never mentioned we have phorids in the genus Pseudacteon, also known as fire ant decapitating flies, here in L.A.

Fire ant decapitating flies do just as their name implies. When a female is ready to lay an egg, she locates an unsuspecting worker ant and injects her egg into the thorax. As the larva develops it migrates into the head capsule and molts a number of times. Through this entire process the ant behaves normally. However, just before pupation, the maggot begins to consume the tissue inside the ant's head, which causes the ant to act oddly, and soon after, to expire. The head falls off and the mouth parts are pushed out, so the oral cavity is clear. As the larva pupates, the adult fly emerges from the now-clear oral cavity of the ant. How's that for an alien ant birth?

Later that day, Brian wrote an e-mail to the homeowner where the trap was located in Glendale:

"Your backyard trap got something unusual- a phorid fly (the group of insects I study) of the genus Pseudacteon. The flies in this genus are all ant parasites, developing in the ant's head, and are referred to as 'ant-decapitating flies.' Usually, in suburban areas, the ant hosts of Pseudacteon are eliminated by the introduced Argentine ant, but you must have (or be close to) a healthy native ant fauna!"

This, as Dr. Luis Chiappe, Vice President of the Museum's Research and Collections Department, put it, "is the power of science!" The presence of this parasite, allowed Brian to infer the presence of the host. If we went out to Glendale today, we'd likely be able to find native fire ants somewhere close by! And I know you all dying to join me on that adventure.



(Posted by: Lila Higgins)