A firefly at night (photo: “Emmanuelm”)
The project has been running since 2008, and has accumulated over 30,000 observations so far (mostly from the US – see map above), which are available online. The graph below shows the result of fitting a family of Gaussian “bell curves” to the data. Observed firefly numbers peaked around June 23 each year (day 174 when it’s not a leap year), with a slight increase in the height of the peak over time. There seems to be no significant change to the timing of the peak.