Stinkhorn and Flies

Top Photo: Fruit flies feed upon the sporogenous gleba of a Ravenel’s stinkhorn on the Dinosaur Trail.

While gazing down at the Ravenel’s stinkhorn next to the Alamosaurus on the back side of the Dinosaur Trail, I noticed one large fly, a flesh fly, and many more much smaller Diptera (about 2mm in length).

Ravenel’s stinkhorn attracting flies on Dino Trail.
The sticky, slimy, gelatinous gleba of the stinkhorn mushroom attracts flies and other insects via its odor.

The little flies had red eyes and looked to be fruit flies. The first thing that came to mind was indeed, fruit fly. But I couldn’t be sure. I didn’t know much about the various flies attracted to stinkhorns and knew there could potentially be hundreds if not thousands of species likely drawn to such fungi.

Fly on stalk of mushroom.
A fruit fly?

After all, the stinkhorn is a specialist at attracting flies and other insects to its stinky mass of gleba which is saturated with the mushroom’s spores. The insects both spread the spores across the landscape via their own feces, after ingesting the sweet, yet foul smelling mass, and from having the stinky substance adhere to their legs and feet. When they fly off to later land on a piece of dung or rotting flesh in another location they may drop the spores which potentially germinate.

Small red-eyed flies on the sticky and stinky cap of the mushroom.

The mushrooms sprout from what are referred to as eggs or volva. They are frequently seen in wood mulch. I’ve identified at least three species of stinkhorn on the museum grounds, all in mulch placed there by our landscaping crew. They are, Devil’s stinkhorn (Phallus rubicungus), Elegant stinkhorn (Mutinus elegans), and Ravenel’s stinkhorn (Phallus Ravenelii)

“Eggs” waiting to “hatch.”

Wanting to know the identity of the red-eyed flies on the mushroom, I decided to upload several photos to Bugguide.net

…an online community of naturalists who enjoy learning about and sharing our observations of insects, spiders, and other related creatures…Using the best resources we have access to, we are creating a knowledgebase to help each other and the online community…

There, someone with much more knowledge on the subject would see the images and hopefully identify them as to species.

As of now, they’ve been ID’d down to the sub-family level.

Order: Diptera

Family: Drosophilidae

Subfamily: Drosophilinae

The family Drosophilidae includes over 4,000 species, about 3500 in the subfamily Drosophilinae alone.

They were fruit flies alright (vinegar flies), attracted to rotting fruit and fungi. The flies in the photos seem to be feeding on the gooey material on the cap of the stinkhorn, which mimics the odor of rotting organic matter. They didn’t seem to be feeding on the stem of the mushroom.

While I still don’t know what species or even genus these flies belong to, I’m satisfied in knowing they belong to the family consisting of fruit flies. Perhaps someone on Bugguide.net will identify the tiny insects further. Until then, fruit fly is close enough.

A new emerging stinkhorn.
Vinegar fly on stem.

So, what have you seen lately?

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