Should you find a creature in or near your home, you do not immediately recognize, identification is important to determine if it is a potentially harmful insect. Many possible worm or wormlike creatures inhabit fountains.
However, one of the most likely culprits is the larval form of the drain fly, an insect known for living and breeding in standing water.
Drain Flies and Their Larvae
Drain flies may not immediately come to mind when homeowners think of the most common indoor flies, as they are far less common than the housefly or fruit fly. Drain flies easily become nuisance pests in homes providing favorable conditions.
Spending most of their time in the gelatinous muck that builds up inside sewage plumbing, drain flies move indoors when attracted by standing water, particularly water that has been standing for long enough to become contaminated. It is not uncommon for homeowners to find adult drain flies or their black, wormlike larvae in toilets, sinks, showers and bathtubs, hot tubs, septic system components or even fountains.
Drain fly larvae are simple enough to remove by hand but does not offer long-term drain fly control. The reason is that whatever drew the drain flies to your fountain originally is likely still there, continually attracting more drain flies.
If you simply remove the drain fly larvae from and do not to exercise further control measures, check the fountain regularly both for the presence of nearby adult drain flies or for new drain fly larvae in the fountain water. If no new drain flies appear, they probably found a more habitable breeding site.
Sanitation and Exclusion
If the drain flies continue breeding in your fountain water, remove the contamination that is attracting the flies. Look for leaking water, mold or algae growth around the plumbing connections on the fountain.
It is possible that the drain flies traveled to the fountain from another nearby site, so check any plumbing connections, septic system openings, sewage system connections for possible sources of contaminated water and clean them thoroughly. If the contamination is in a concealed part of the fountain's plumbing, you may need to clean it out with a long-handled stuff brush or bacterial complex gel.
Other Control Methods
Some pesticides sold in aerosol cans and labeled for indoor control of flying insects offer adult drain fly control. However, drain flies are likely to keep hanging around until contaminants that attract them are removed.
If drain flies are a persistent problem for your fountain and surrounding areas, have a professional exterminator apply a residual pesticide to areas near the fountain that may be serving as perfect living and breeding grounds for these nuisance insects.