It glows without interruption. This photo was taken near Barcelona, Spain.
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2$\begingroup$ It looks like a firefly to me. The fact that it glows is a dead give away, the light producing organ on the abdomen looks right, and the pronotum ( the shield covering the head ) also matches. Many species of firefly have flightless members ( usually female ) that sit on the ground and signal the flying ones. $\endgroup$– user137Commented Jun 23, 2016 at 1:31
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$\begingroup$ My doubt comes from the fact that it glows without stop. In some identification charts that I've looked, they all glow in intervals of at most 9 seconds. $\endgroup$– Federico CanteroCommented Jun 23, 2016 at 6:39
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$\begingroup$ Glowing non-stop does seem weird. That would use up a lot of luciferase, and require a significant input of energy. But I'm pretty sure it's still a type of firefly, I'm not aware of any other bioluminescent beetles. $\endgroup$– user137Commented Jun 23, 2016 at 10:35
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$\begingroup$ Looks like a glowworm to me. $\endgroup$– anongoodnurseCommented Jun 23, 2016 at 18:26
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$\begingroup$ @Federico I know it's been 9 months since this question was answered, but please see my new answer (Feb 2017) addressing the geographic unlikelihood that your specimen is L noctiluca. $\endgroup$– theforestecologist ♦Commented Mar 6, 2017 at 21:13
2 Answers
I'm going to guess this is a Lampyris noctiluca, a species of firefly commonly found in Europe. The females are flightless, glow continuously for up to 2 hours, and are commonly referred to as glowworms, per anongoodnurse's comment.
I think @user137's answer is close, but I believe that Lampyris noctiluca is the wrong species.
This looks like Lampyris iberica (the Iberian Glow Worm). The Lampyris are a genus of european firefly beetles whose larvae and larviform females are among those organisms commonly called "glowworms".
© Prem Rose, 2016. http://www.inaturalist.org/photos/4351809
© Prem Rose, 2016. http://www.inaturalist.org/photos/4351808
These two species are very similar. According to De Cock et al. (2014),
Identification of Lampyris larvae stays difficult [due to a] lack of clear discriminating characteristics.
- See here for more pictures of L. iberica (and here for more pictures of L. noctiluca for comparison).
However, according to work presented by De Cock et al. (2014), L. noctiluca is not found in Barcelona, but L. iberica IS found in Barcelona.
L. noctiluca shows an extreme Northern distribution, only present scattered over provinces in the North Atlantic region and Provinces in the Pyrenees, whereas L. iberica also occurs in central Northern provinces and the Southern extreme of Spain in Cádiz and the province of Málaga.
Both species present a conspicuous sexual dimorphism, with males being smaller and winged and females being larviforme, without wings and noticeably larger than the males.