O. melanopus is native to Europe and Asia, but it has become much more common in the world. In North America, it was first spotted in Berrien County, Michigan, in 1962. Since then, it has spread through the Midwest to the East Coast, and is making its way westward. Significant populations are found in Virginia, North Carolina, Utah, Montana, North Dakota, and Missouri and Iowa. Environmental conditions such as temperature and humidity drastically affect the O. melanopus population for that year. A cold spring favors the host plant, whereas a warm spring favors the leaf beetle. An increase in the general temperature of the planet may allow O. melanopus to spread into Canada. More recent surveys have shown that O. melanopus has indeed arrived in Canada; in 2006, it was present in 11.1% of fields, and in 2009, in 33.3% of fields in southern Alberta. Locally, adults spread to the exterior of fields during their overwinter. Larvae tend to stay on the outside of crop fields, but are also found in the center. Local populations are never homogenously distributed, hotspots and empty places occur in each field.