Q. There are insects flying
around my apartment that I have never seen before. I thought they
were termites at first, but their wings seem too short. Perhaps they
came out of the soil that I brought into the house from the compost
bin? They are about ½ to ¾ of an inch long. Their bodies are green
and they have large eyes. They buzz around quietly and have not
bitten anyone yet. Do you know what they are?
A. You can bring some unwanted guests into your home if you use
fresh compost on your houseplants, especially if it has not broken
down completely. A number of insects feed on decaying organic matter
and find compost irresistible. You would not want to treat your
compost for them because insects work in concert with fungi and
bacteria to break organic matter down into humus.
The writer sent samples that were submitted to Penn State's Insect
Lab for accurate identification. They turned out to be black
soldier flies. They were probably present as larvae or pupae in
the compost the writer used to make a potting mix for her
Compost available at a landscape supply yard
Black Soldier Flies
Black soldier fly larvae feed on all kinds of decaying organic
matter, including compost, manure and carrion. They are not
considered plant pests and will not bother the houseplants. Adults
feed on pollen and nectar, primarily from plants in the daisy and
They do not bite, sting, or transmit any kind of
disease, nor will they damage household goods. It is just a nuisance
to have them flying around your home. No treatment beyond a fly
swatter is recommended because they will die out when the organic
matter in the potting mix breaks down completely.
Treating compost for houseplants
Although organic matter is extremely beneficial for houseplants, you
should screen it and allow it to air dry to reduce the
possibility of creating a nuisance in your home. Many of the insects
that live in compost will not survive if it is thoroughly dried. To
be on the safe side, you might want to pasteurize compost
before using it on houseplants. Be warned -- baking compost stinks!
Place it in a shallow baking pan -- inexpensive foil pans are ideal.
Heat the compost up to 180 degrees for 30 minutes. Use a meat
thermometer to check the internal temperature. You might consider
doing this on an outdoor grill to avoid smelling up your house.
Another option is to get a worm bin. Known as
vermiculture, this composting process uses red wigglers and
other species of worms to turn vegetable scraps, coffee grounds and
other non-meat food waste into a nutrient-rich organic matter that
is ideal to incorporate into potting mix for houseplants. The worms
live in a sealed bin partially filled with shredded newspaper for
bedding. When you "feed" them food scraps, it is important to cover
them with a fresh layer of shredded paper to avoid attracting fruit
This a great composting method for apartment dwellers -- they do not
smell or take up much space, and the worm castings produced are an
excellent source of organic matter and nutrients for indoor plants
as well as those in your landscape. The only problem is that once
you see the positive effect the worm castings have on your plants,
you will want more than a single bin will produce!
Pennsylvania Resources Council offers training in vermiculture
and backyard composting.
Composting for the