Black, flightless little jumping fly with strong back legs
February 27, 2010
I have been discovering these black little bugs (1/4″ long) on our upstairs window (inside). They have heads and antenna like bees, small wings, black bodies, strong rear legs and don’t seem to want to fly. They crawl and jump with their strong rear legs (note the red muscular part). They seem to prefer hanging out on the white, vinyl part of the window. They continue to appear on this same window every so many days. I don’t know where they come from and what they are.
We live in Seattle, Washinton

Chalcid Wasps

Hi Doon,
IN our opinion, these are Small Carpenter Bees in the genus Ceratina, which is pictured on BugGuide.  They may be emerging from an indoor nest, though we are not certain if these bees nest in treated wood.  We are contacting Eric Eaton request his opinion.

Hi there,
Thanks for your prompt reply.
Carpenter Bees?!? That would be bad news, especially if they are coming into the house from a nest in the wall…wouldn’t it? I know they are not mean, but they do do damage.
I took a look at the pictures and see a definite similarity, but my little guys have these strong back legs. Did you notice the reddish bulging bit on their legs? They all have them and use them to hop, it seems.
What else could they be?
Looking forward to what Eric has to say.
Thanks, guys. What an awesome service!

Chalcid Wasp

Eric Eaton makes a correction
Hi, Daniel:
Those are not small carpenter bees.  They are parasitic wasps in the family Chalcididae, as confirmed by their swollen hind femora (“thighs”), among other characters.  They may have emerged from a cocoon or something.

I saw the update. Thanks!
I guess the real question is, how are they getting into my house and what are they doing there?

Hi again Doon,
There have been two letters from yesterday that have needed a bit more attention from us today, and yours is one. Regarding wasps in the family Chalcididae, according to BugGuide: “Most are parasites of other insects, mostly of eggs or larvae
” and “They are used as pest controls because they parasitize mainly the orders that contain many common pests: Lepidoptera, Diptera, Coleoptera and Homoptera.”  Identifying the exact species is a bit beyond our capabilities, but one of our readers might be able to supply you with a response.  We would recommend that you provide a comment to our posting, and then you will be notified automatically if an expert in the Chalcids can provide you with an accurate identification in the future.  Speaking more generally, we would surmise that an insect (or insects) that was (were) parasitized by the ancestor of your generation of Chalcids entered the home and died.  Once their life cycle was completed within the body of the host species, your generation emerged and will continue to seek out the hosts if there are any remaining.  Most species that parasitize others are species specific.  The orders that were mentioned as common hosts are Lepidoptera (butterflies and moths), Diptera (flies), Coleoptera (beetles) and Homoptera (true bugs and relatives) and each of those orders have individuals that often enter homes.  We would also like there to be a resolution to this mystery.  We suspect your current generation of adults entered your home as larvae, transported by a host insect that had been parasitized.  The adults emerged from the corpse and are being attracted to the light of the window in an attempt to get outside if there are no further hosts to parasitize.

Hi folks,
Finally, I think I have discovered the mysterious source of my Chalcid friends!
I was up in the attic this morning. We had a dead rat in one of the traps. All around the carcass of the rat were these brown little pupae. After doing some research, I discovered that these were fly pupae. Then, on one site, I came across a photo of a chaclid wasp (or parasite fly) depositing an egg into a fly pupa:
And here is the likely story: rat comes in and gets caught in the trap, dies. As it decomposed, flies lured to the stench flew in through the roof vents in the attic and did what they do best. Later, after the fly maggots went into their pupal stage, the chalcid wasps came and did what they do best.
Mystery solved!
Thanks for your help!

2 Responses to Chalcid Wasps in the home: What species? and What is the host insect???

  1. Joyshree Chanam says:

    Hi, I came searching for identification of the same wasp! my search words were: “small black wasp with strong hind legs”. I found this pupa on a mint leaf ( part of a bunch I had bought from the market). I wondered what butterfly/moth caterpillar would like to eat mint leaves which have such strong smell. So i kept the pupa in a jar with ventilation, and after two weeks, today morning i saw a wasp! Now I think I can connect the dots. Some Lepidoptera caterpillar on the mint got parasitised by this Chalcid wasp either at larval or pupal stage. I will release it in my garden so that it can do some pest control:) Thanks a lot.

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