Fireflies of the American genus Photinus Laporte, 1833 are widely distributed through North America, and particularly diverse in Mexico (Green, 1956; Zaragoza-Caballero, 1996; Zaragoza-Caballero & Viñolas, 2018; Zaragoza-Caballero et al., 2020). Recently, a new species of Photinus was described from the Iberian Peninsula, representing the first record of the genus for the European continent (Viñolas et al., 2018; Zaragoza-Caballero & Viñolas, 2018). The species is considered an alien in Europe that most likely comes from Mexico or the USA. It has been recorded in several localities throughout Girona province, Northeastern Iberian Peninsula (ZaragozaCaballero & Viñolas, 2018), where its range might be expanding. Here we present the first record of the larvae of P. immigrans and some notes on their natural history.

During a summer field trip hundreds of adult male P. immigrans (Fig. 1a) were observed in the locality of Fonolleres, Girona (42.0201°N, 3.0542°E, 14m, August 19^th, 2020), flying and flashing over corn fields just by the village soon after dark, in proximity with female specimens of the native Lampyris iberica Geisthardt, Figueira, Day & De Cock, 2008 (Fig. 1e). We visited the same locality in autumn (November 16^th, 2020) trying to locate and photograph P. immigrans larvae, but we could only find larvae of Lamprohiza mulsantii (Kiesenwetter, 1850) (Fig. 1c) and Lampyris iberica. In the nearby locality of Ullastret, Girona (42.0089°N, 3.0778°E, 20m), in an area with wheat crops and small patches of natural vegetation dominated by Quercus ilex L., we also located larvae of L. mulsantii and Nyctophila reichii (Jacquelin Du Val, 1859) (Fig. 1d). In a new survey, during late winter at the same spot in Fonolleres (February 24^th, 2021), we found 11 larvae of P. immigrans (Fig. 1b), superficially buried in a recently ploughed (less than a week) corn field.

De visu description: the larval sizes were ca. 10–15 mm length, with elongate vermiform body (Fig. 1a); observed larvae had 3 thoracic segments and 8 abdominal segments, all tergites were divided by a sagittal line in dorsal view; coloration was dorsally black to dark brown, each tergite had 2 longitudinal light-brown to reddish stripes laterally oriented and widened at posterior part. All specimens had pink lateral pleura and were ventrally lighter than dorsally. The specimens did not show bioluminescence at any point, when found or when disturbed.

The larvae of this species were found buried in the removed soil of a ploughed field, in the first 10–15 cm. By comparison, the native firefly larvae were found in all cases under rocks and debris, and they were not observed in strict syntopy during our surveys. According to the bibliographic records, other species of Photinus overwinter for 1–2 years as subterranean larvae, and feed mainly on earthworms and soft-bodied insects before pupating during early summer (Williams, 1917; Hess, 1920). This different trophic niche exploitation may account for low trophic competition between P. immigrans and the native species. De Cock & Guzmán-Álvarez (2013) reported that some Iberian fireflies occasionally might feed on earthworms, but they preferentially feed on snails and slugs (Haddon, 1915; Symondson, 2004; De Cock & Guzmán-Álvarez, 2013). Mating behavior is also quite dissimilar among P . immigrans and most native Iberian species. In Photinus fireflies, males produce courtship flashes while flying and females reply to the preferred male with their own flashes (Cratsley & Lewis, 2003), whereas males of sympatric native species do not flash during flight and they are usually found flying looking for the continuous cold light produced by apterous females (Geisthardt et al., 2008; De Cock, 2009; Novák, 2017, 2018). We hypothesize that interaction should be low between the alien P. immigrans and the sympatric native species. However, the species might potentially interfere with species with comparable mating behavior, like Luciola lusitanica (Charpentier, 1825), which was recorded historically in the Pyrenees, although its presence is not confirmed in this area (De la Fuente, 1931; De Cock & Guzmán-Álvarez, 2013; Constantin, 2014). A detailed study of interspecific competition and the putative effect of P. immigrans on the native firefly species and their prey is pending.

With this contribution we hope to facilitate the identification in the field of larval stages of this exotic species. A detailed description of all stages and larval instars is still needed, for which it is necessary to have access to abundant material including all larval stages. However, the information and images provided in this article will help to identify new populations of P. immigrans and track the colonization of new geographic areas during all seasons, as adults are only active in the summer months.