“I returned from a holiday to find these worms swimming in our toilet”, writes Siobha about the black creatures pictured below. “What are they?” We have to admit that, were it not for the size and color of the worms, as well as the location they were found in, we would not be able to identify these creatures based on the photo and video alone, because the quality is simply not that good. Fortunately, we can make an educated guess based on the aforementioned factors: we think these are drain fly larvae. As their name suggests, drain fly larvae are the immature form of a species of fly that like to infest drains. They are not harmful, but they can be quite a nuisance.