The Answer: Marsh Fly, Snail-Killing Fly, Tetanocera ferruginea

     We did it!

     The question:

     “Can you help me identify this insect?

     Has an answer:  Marsh Fly, Snail-Killing Fly, Tetanocera ferruginea

It was a thrill to follow the suggestions of helpful blogging buddies… your suggestions ultimately led to the three keys that unlocked the mystery:

  1. Biodiversity in Focusa blog authored by an entomology graduate student and nature photographer
  2. Bug
  3. Encyclopedia of


“What I think you’ve found is a species of marsh or snail-killing fly in the family Sciomyzidae.”
Morgan D. Jackson

And what an interesting insect this one turned out to be…

Marsh flies are generally slender, yellowish or brownish, 1/4 – 1/2″ long. They have fairly prominent eyes, prominent forward-pointing antennae, and bristles on the femora (upper hind leg). The wings are mottled with various light brown markings according to species.

Marsh fly larvae prey on or become parasites of slugs & snails.

Habitat: Near ponds, streams, marshes.

Range: Throughout North America.

Food: Adults drink dew, nectar, and tree sap.


Sighted: October 26, 2014
Location: Glencoe Swale, Hillsboro, Oregon
Size: 3/8″


  1. Oh. Well it was a fly, anyway. 🙂 And it does like fruit, once out of its teens at least.

    Hmm, ferruginous means rust-coloured… I should start a local promotional campaign on behalf of little Rusty Tetanocera, because in gardens around here, what the deer don’t eat the slugs will polish off. Go, Rusty!


    1. That was pretty exciting to learn that this little organism in the biodiversity puzzle does its share to cut down on slug/snail culprits. I just hope it won’t harm the Robust Lancetooth Snails… they prey on slugs and other snails, too! (

      BTW- I suspect I will have trouble recalling the Tetanocera ferruginea portion of this fly’s name… but I certainly will remember the nickname, “Rusty!”

      Liked by 1 person

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