Good Guys Flies

EmeraldValley-EPC-CO_LAH_0773fSomeone left the screen door open, and suddenly our house is full of annoying, buzzing, flies. They circle the kitchen while I’m cooking, tangle with my hair while I’m sitting at my computer, and zoom past my Kindle when I’m reading in the evening. I have to ask, did we really have to have flies, God?

Fly on Ipomoea leptophylla_Bush Morning Glory_ChicoBasinRanch-CO_LAH_3872Yes, we can definitely do without some flies. House flies are not just a nuisance. According to Penn State’s Department of Entomology, they “are strongly suspected of transmitting at least 65 diseases to humans, including typhoid fever, dysentery, cholera, poliomyelitis, yaws, anthrax, tularemia, leprosy and tuberculosis. Flies regurgitate and excrete wherever they come to rest and thereby mechanically transmit disease organisms.” Pretty gross!

It’s not just house flies. There are over 4,000 species of biting midges in the family Ceratopogonidae, better known as no-see-ums. They are so small they fit through all but the finest screens, and their bites itch for several weeks, as I can attest. They, too, can carry diseases, especially in tropical areas.

Fly_BitterLakeNWR-NM_LAH_8000-001Then there are various black flies, such as the ones I encountered in New Mexico (left) that attacked me through two layers of clothing and a heavy application of DEET. They carved out enough meat to start a deli!

On the other hand, not all flies are pests. Some are even beneficial. Who would have guessed?

I was up in the mountains taking pictures of wildflowers when I got so distracted by the bizarre insects on the blossoms, I forgot all about the flowers. These brightly colored, bristly critters were fascinating! I couldn’t wait to get home and look them up. What could they be?

I was absolutely astonished to discover that I’d captured images of a Spiny Tachinid Fly. That’s a fly? It didn’t look anything like any fly I’d ever seen!

Adejeania vexatrix_Spiny Tachinid Fly_WestonPass-CO_LAH_1885-001

I learned that around 10,000 species of tachinid fly have been identified worldwide, separated into over 1,500 genera, and that entomologists expect another 5,000 species still remain to be discovered. Around 1,300 species live in North America. And that’s a good thing.

Emerald Valley-EPCo-CO_LAH_5477Tachinid flies are parasitic. Thankfully for us vertebrates, they only parasitize other arthropods, primarily  insects such as beetles and caterpillars. Some are picky eaters, only dining on a particular species of host, while others are generalists. In a number of cases, these flies play a significant role in reducing populations of insects we consider pests.

It’s a brutal bug-eat-bug world out there. The tachinid eggs get into a host in a variety of ways. They may laid on a leaf, to be ingested along with dinner. Or, the eggs may be laid directly on the host’s body. When they hatch, the larvae tunnel into the host. In a few cases, mama uses a sharpened ovipositor to directly inject them. No matter how it happens, once those larvae are inside, it’s bad news for the host.

As they grow and develop, those larvae eat their host from the inside out. Amazingly, the infested host can live for quite a while, providing bed and breakfast for an entire family of fly larvae. Imagine if you had a dozen or two large maggots feasting on your innards—while you’re still using them! Who needs a science fiction thriller when science facts are so terrifying?

Tachinid fly_RamahSWA-CO_LAH_1934fThere was a reason I noticed my first tachinid fly in the mountains. They can survive at higher elevations than can bees, making them important pollinators above the tree line. The adult flies genteelly sip nectar, or suck up the honeydew produced by aphids and scale insects.

Tachinid flies can be house fly-sized, or a bit larger. Most are relatively dull looking and look like hairy house flies, although a few varied species come in colors ranging from metallic blue or purple to orange or yellow, like the ones I first photographed. They’re most easily identified by the alarming number of bristles that cover their bodies. I suppose being spiky  offers some protection from being eaten. They’d certainly stick on the way down.

I’m glad to know that some flies are on “our” side. Now, can anyone tell me about a beneficial mosquito?

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