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Biodiversity Blog



 Photo: Alex Wild

Austin sits at the far southwestern corner of the range of the Eastern Firefly (Photinus pyralis), the species that gives eastern landscapes the characteristic dusk light show in early summer. This insect is common in neighborhoods around Austin, with large flights in April, May, and June and a smaller emergence when the weather cools in October.

Fireflies- true beetles, rather than flies- spend most of their lives out of sight, taking two years as subterranean larvae to develop into the more familiar adult forms. Larvae resemble a stout, armor-plated worm in appearance and are predaceous, hunting insect grubs, slugs, and other invertebrates. After their second winter they emerge as short-lived, non-feeding adults.

 Larva. Photo: Alex Wild

The visual display is courtship behavior. The famous fireworks are fireflies using light to find and evaluate potential mates, and firefly species, like songbird or cricket species, can be recognized by their unique signals. Some flash in pulses, some in long streams; some in blueish green, some in yellowish-orange; some at dusk, some at midnight. Our common Photinus pyralis flies at dusk, earlier than most species, in a characteristic j-shaped swoop near the ground. Typically, the male signals a bold flash from mid-air and hovers, watching, waiting, for an earth-bound female to aim a dim flash back. If he sees a return signal he flies closer and repeats the cycle, until the female either accepts him or decides his flash isn’t to her liking and she goes dark.

 Photo: Alex Wild

The flash is produced by a light organ at the tip of the abdomen. Chemically, the flash is an energy-intensive process where an organic molecule, luciferin, releases light in the presence of oxygen, the energy-transporting molecule ATP, and an enzyme, luciferase. The process has been widely used in biological research, as the light-producing molecules can be inserted into other genetic sequences as a tag to help scientists see if their experiments have worked.

If you have a yard and would like to encourage fireflies, we recommend the following:

Leave a portion of your yard- perhaps along a back fence or part of a perennial garden- in untilled leaf litter. Larvae need habitat too!

Provide low flowers or ground vegetation to around knee- to waist-height. Female fireflies require good perches.

Refrain from chemical pesticides. Fireflies, like most insects, are susceptible to even the “natural” chemicals marketed for mosquito control.

Keep your outdoor lighting dim enough so the fireflies can easily see each other.


 Photo: Alex Wild
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