Dark Winged Fungus Gnat – Larvae
Q: Recently, large groups of worms have been crawling onto our patio from the lawn. It is hundreds of them moving as a single unit. When sprayed with insecticide, the cohesive group breaks up and they die quickly. The next morning, there are several more groups of them on the patio.
A: I have never seen anything like this so I sent your photos to the good folks at www.BugGuide.net . They were fascinated with the creatures as well.
Their decision is that your “worms” are the larvae of dark-winged fungus gnats.
Fungus gnats are usually pests of indoor plants. They bore through potting soil and eat plant roots. Outdoors, when a lawn has lots of organic matter or thatch, the larvae can hatch in such numbers that they travel as a group…which is what you saw.