Common harvestman

The common harvestman (Phalangium opilio) is not native, but it is very common and widespread in North America. It is the most commonly encountered harvestman in many parts of the United States and Canada, especially in disturbed or urban areas. It is particularly well-adapted to live in human-modified habitats like gardens, yards, and even on the exterior of houses. It is known for its preference for vertical surfaces like walls and tree trunks, which makes it a frequent visitor to windows and siding. Therefore, if you find a harvestman on a window screen or the side of your house, it's very likely to be Phalangium opilio.

Phalangium opilio often has a distinct dark, saddle-shaped marking on its back, and the legs can have faint bands. Coloration on females is highly variable. Some Leiobunum species are also quite common in human environments. Their legs are often exceptionally long and tend to be more strongly banded than P. opilio.

The harvestman in your photo doesn't appear to be a Leiobunum species, primarily due to the proportionally shorter leg length. While a definitive identification isn't possible from this photo alone, the combination of its appearance and location makes it highly probable that this is a female Phalangium opilio.