CLOSED: Help me ID this fly, please

Fort Worth, TX(Zone 8a)

This is a tiny fly that is often mistaken for an ant. It sucks the life out of caterpillars and chrysalids left outside. Even screen will not keep them from destroying butterflies. They are so small they can crawl through standard sized window screen squares.

The mesh holes in this photo are half the size of ordinary window screen squares, and the little fly is almost small enough to squeeze through. So far it works to keep them out...Meanwhile, exactly what are these things?


Thumbnail by debnes_dfw_tx
Fort Worth, TX(Zone 8a)

Still waiting on someone to help me figure out exactly what this little preditor is.. I need to know their life cycle and anything else I can find out about them.


Newburgh, IN(Zone 6a)

I looked on this site and there is a lot of information. You could look here and see.
The picture you have is to small. Hope this helps. Scroll down to the fly section.

Lincoln, United Kingdom(Zone 8a)

Deb, if it looks like an ant it could be a Sepsis, I have Sepsis fulgens but they feed on nectar and the larvae on dung. They look like a cartoon character running about then waving their wings about! They are as small as a very small ant.

If it is a Sepsis, then something else could be parasiting on the caterpillars as many things do.

The Woodlands, TX(Zone 9a)

Are you saying that this insect sucks the life out, or does it lay eggs in the cats and chrysalises (is that a word?) and the resulting larvae suck the life out?

Fort Worth, TX(Zone 8a)

It's hard to see, I was hoping by finding out what they are, that I could see where they are coming from. I have observed them on the chrysalids and figured they were eating by making a tap. It very well could be that it was helping his siblings out of the chrysalis. In that case it is even more disturbing.

When I look up caterpillar parasites online, I find mostly sites where they take a morbid joy by introducing them and even marketing them. I don't know if the flies I have are those particular bugs or not. I have to apologize for not knowing more at this point. I am hoping someone who has had experience with these can clue me in.

If they are coming out of the chrysalids, I need to know if the hatched flies are capable of harming other chrysalids right away? Is their turn around to adult that fast? If so these tiny things can become a ginormous problem!!

In any case I am looking for all the knowledge I can to override their damage.


The Woodlands, TX(Zone 9a)

It's possible that this is a tiny braconid wasp that lays its eggs in chrysalises or cocoons...The eggs hatch inside, the larva pupates inside, and an adult wasp emerges from the cocoon. This would leave a small hole in the cocoon. Or several if there were several eggs. Other species parasitize aphids, caterpillars, beetles, just a whole lot of insects. They are considered beneficial because they take out a lot of the pests. However, not so good in a butterfly garden, as you know.

They wouldn't be helping siblings out. Nor tapping into the cocoon.

Tachinid fly was another possibility, but I don't think they are that small. You wouldn't be able to see Trichogramma wasps - half a dozen can fit on the head of a pin. They parasitize insect eggs.

Salt Lake City, UT

Is this bug also a Sepsis? There are hundreds of these things swarming around outside my house in Salt Lake, and I am trying to figure out if they are harmful to my garden or buildings. I am new to the area, so I don't know the local insects.

What attracts them/causes them to thrive?

Thanks in advance,

Thumbnail by chuky
Lincoln, United Kingdom(Zone 8a)

chuky, the eyes on your bug are wasp-like so I would say it is some sort of wasp, there are thousands of different types and some don't even have a species name.

Some wasps are parasitic to other bugs laying their eggs in their nest, they also help to keep down the insect population by eating other bugs.

Flies have a small balancing mechanism behind their wings as they only have 2 wings, this can often be easily seen when the wings are spread.

Salt Lake City, UT

Wallaby1, here is another shot of the same insect - perhaps this allows for better ID? My biggest concern is that this not be a house damaging insect, but since I am not from this area, I have no idea what "bad" bugs, ie. carpenter ants, look like.

Thumbnail by chuky
Lincoln, United Kingdom(Zone 8a)

chuky, I have looked at many sites trying to ID all sorts, including wasps, it has wasp eyes so would belong to that family but there are so many. If it's a common one you might find it on the Bug guide site, the detail in your first pic does show quite well the abdomen.

Fort Worth, TX(Zone 8a)

Well folks! I haven't solved this 'exactly' but I do know where the flies are pouring out of.

I isolated some of the chrysalids and later checking there were about 50 little flies in the cage with them. I found the one they were streaming from, and took care of it.
I think I know enough to possibly prevent this from happening to some in the future. Amist all the 'benificial' insects, there is a lot of conservation to attend to. Certainly I have my work cut out for me.

I think I saved the Giant Swallowtail chrysalids, already released about 50 butterflies this year.. Giant STs, Black STs, Gulf Fritillaries, and Pipevine STs. I have 3 Monarch cats in safety now, and some Silver SPotted Skippers. More species on the way, and so far they are relativlely safe.

Thank you all for your comments and help!

Warm Hugs to all,

Salt Lake City, UT

Okay, so I think that these are "sweat bees". Any idea how to discourage their hanging out around the front of my house? There are hundreds of them all around my front patio - it almost looks like my front porch is covered in flies. Something must be attracting them, any ideas?


Fort Worth, TX(Zone 8a)

Not sure chuky, Mine go straight for my caterpillars.. Mostly Gulf Fritillaries and Black Swallowtails.. I resorted to the best thing I could do to save the cats, and it's working very well for me. I will be going to the Library when I get time to do some more research. So far I found my best defense is a good defense..
Here is the solution that is working>

Thanks for all your help everyone, It is good to know about all of these kinds of bugs, like some of you have posted.
I suppose I will mark this solved for now, and maybe resurrect it just to give the final word on what I have here. I will keep it on my watch threads.
Thx again all!

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