The latter might be the most likely suspect in the case of Photinus marginellus, the type of firefly that seems to be the most common in Ann Arbor. Of the nearly 200 firefly species in North America, they are among the poorest fliers and thus highly site-specific. If the patch of ground they inhabit is wiped out, so are they. But this doesn't explain the decline in the Lords' yard, which remains a great firefly habitat. So maybe it's just that we had an unusually cool June and July this year.
What's a firefly lover to do? Minimize outdoor lighting. Forgo pesticides and bug zappers. Leave some deadwood in the yard for larva habitat. It is, admittedly, not much.
"We've just made it hell for fireflies and everything else," Lloyd says. "It's not like they can pack up and leave. They die out."
[Originally published in August, 2009.]