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The Light Organs of Fireflies
The light organs of fireflies vary greatly across the family. In the more derived taxa, the light organ is made up of two distinct layers: the dorsal layer and the photogenic dorsal layer. The dorsal layer is thought to reflect the light of the photogenic layer outward from the body to maximize its intensity. The photogenic layer is made up of photocytes and is the layer where light production occurs. The structure and composition of the two layers vary depending on the genera, life stage, and/or sex being observed.

While some firefly genera have structurally basic light organs with a simple tapering tracheal system, others have structurally complex light organs with intricate tracheal networks that contain multiple elements. In taxa with more advanced light organs (such as Photinus), the tracheal system is made up of a cylinder, tracheal trunk, tracheal branches, tracheoles, tracheal twigs, tracheal end cells, and end cell processes. It it believed that there may be additional processes, though limitations in optic resolution have prevented these structures from being described.

All known firefly larvae produce light, though only some species do as adults. The purpose of light production in larvae is generally accepted to be a form of Aposematism. In adults, light production is usually noted as a form of communication for mating purposes, though it may serve as aposematism as well. The production of light is believed to have evolved multiple times across the family with no single origin.

Light signals vary greatly in Lampyridae. Both the larvae and adults of some fireflies produce a rising and falling or pulsating glow and others a consistent glow. The adults of some species are known for a having a great deal of flash control, with multiple rapid flashes occurring in a specific pattern to communicate with other individuals of the same species. These rapid flashes may deviate from their normal pattern when the firefly is disturbed, suggesting that it is still used as an aposematic function. Adult fireflies have also been observed being avoided by bats, suggesting that their bioluminescence functions as an advertisement for their distastefulness.

Systematics
Our understanding of firefly systematics is constantly shifting as new information is obtained about the family. The status of what families are sister to Lampyridae is still being debated. Some authors speculate that Rhagophthalmidae has a polytomy relationship with Lampyridae while others have found evidence that Cantharidae and Lycidae are sister to Lampyridae.

One major discrepancy in much of the literature is on which subfamilies are actually recognized. The newest published total evidence phylogeny suggests that there are six monophyletic subfamilies with high support: Ototretinae, Cyphonocerinae, Luciolinae, Amydetinae, "cheguevarinae" (unpublished), and Photurinae. Lampyrinae shows evidence of monophyly as well, though four taxa within this subfamily make it paraphyletic. Ultimately, there does not appear to be a universal agreement on definite subfamilies.

* Points in the current article that need citations:


 * 1) Luminescent diurnal fireflies?
 * 2) All of the systematics section