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Beetle blog

1 Post tagged with the phengodidae tag

Let your love Glow…

Posted by Blaps Feb 13, 2013

Happy St. Valentine’s Day beetlers!


When we talk about love it’s a subjective thing, and often attraction is in the eye of the beholder. What attracts us to one thing more than another we cannot fully explain; but, what we can explain are some very specific and perhaps even artful methods of attraction employed in the beetle world. This St. Valentine’s we honour that most successful paramour of love, the Glow worm!


Glow worms are beautiful creatures, at least when they light up! However, upon inspecting our collection, I find it is quite hard to see them as being very attractive at all.



A rather uninspiring drawer of Phengodidae glowworms from our collection
Image courtesy of Helena Maratheftis 2013


Instead of investing their energies into metamorphosing into  the multifarious morphologies possible within the Coleoptera such as beautiful metallic colouration, impressive horns and armature,  clever methods of mimicry and disguise, they are in fact for the most part, small, soft bodied and brownish – in effect, not sexy; but perhaps a hidden nature is yet to be revealed! Yes, come cover of darkness, a mysterious transformation occurs, and what this drab exterior belies is revealed in all its brilliant neon glory!  Yes, glow worms glow!



Lampyris noctiluca courtesy of Devon Wildlife Trust



What is a glow worm?


Well you may have gathered by now that glow worms are not actually worms – they are beetles! Currently there are two families that could be considered glow-worms in popular understanding, the Phengodidae (which includes the famous ‘railroad worm’) and the Lampyridae (which includes the common European glowworm Lampyris noctiluca). The Rhagophthalmidae warrant a mention as formerly they were included as a subfamily within the Phengodidae – but the jury is out on their taxonomic placement. Let’s just say they are related, as shown by the bioluminescent organs found in the larvae which are known as star-worms). They will probably end up as a subfamily within the Lampyridae.


The term worm probably derives from the female of the species which in many of the glow worms, despite undergoing a full metamorphosis, remains in what we call a larviform state. She will resemble the larvae with the exception of possessing compound eyes, often a hardened plate covering the head and differ somewhat in the number and position of ‘lanterns’ – the paler segments that transmit bioluminescence.



Lampyris noctiluca from top to bottom: adult male, larviform female and larva
Image courtesy of Helena Maratheftis 2013


And the reason for this rather lazy metamorphosis? Well would you bother to get out of bed if you could make your bottom glow like a glow worm?! Probably not! There is no advantage, particularly in terms of energy investment for the female to produce wings, or even to have the ability or desire to feed as an adult. All she wants and needs is to mate; or if we want to be a bit more romantic about it, and in the sage words and lyrics of Girls Aloud (c. 2004) she is a ‘love-machine’.



Calyptocephalus fasciatus; Lampyridae type held in the Museum's collection - complete wtih magnificent antennae!
Image courtesy of Helena Maratheftis 2013

The mating game


Perhaps we are not always aware of how complex our mating rituals can be. In the ‘glowworms’ the bioluminescent function is a ‘come-hither’ signal to wanton males. Given that the females often-times will only have a maximum of two weeks, if that (please bear in mind everything written here is a generalisation for the purposes of description – these behaviours will differ between families, genera and species) in which to attract a male, mate, lay eggs and then die, all of this without even stopping for a bite to eat* timing and the ‘attractiveness’ of the signal is paramount!


The ‘signal’ – the bioluminescent pulsing or flashing is a kind of Morse-code-love unique to different species. Throughout most of England in the summer for example, the female Lampyris noctiluca can be spotted at dusk climbing low herbage in order to elevate herself and gain as clear a pathway to her prospective male as possible, then it’s all systems go and she starts signalling. This signalling will go on until she has successfully mated; sometimes she is not successful on the first night; we all know that feeling!


Fatal Attraction


*In some of the Lampyridae, in particular the genus Photuris, the adults do feed; and with a somewhat macabre intent. Females of the genus are little minxes often referred to as the ‘femme fatale’ firefly! They are able to mimic the signalling of other species, which lures unsuspecting males to their deaths! The Photuris females need a defensive chemical that is found in the male (it would make less evolutionary sense to eat one’s own species!) in order to repel potential predators. This chemical is only secreted when the beetle is attacked. By consuming this chemical (known as Lucibufagin) the female boosts her predatory defences and lives to mate with her own kind!



A very attractive male of the Pseudophengodes genus
Image courtesy of Helena Maratheftis 2013



Love glow


The ‘glow’ differs between species and can serve a different function. The glow in the larvae is almost certainly evolved to deter would-be predators (though the larvae are voracious predators themselves, enjoying the odd millipede or slug!). In the adults, both males and females can signal, but in some species it can only be the female that lights up. There are also different frequencies of signal that are species specific and some species will aggregate en-masse and signal in unison! Some species’ adults do not signal for mating purposes, rather as a warning to predators and instead use pheromones to attract their mate.


Bioluminescence is a chemical reaction producing a ‘cold light’ with no infra-red or ultra-violet frequencies, and is the most energy-efficient form of light that we know and it involves a good deal of attraction!   Luciferin is the substrate and Luciferase is the enzyme, in the presence of magnesium, oxygen and Adenosine-5 Triphosphate (ATP) (present in all living organisms) the chemical reaction takes place within the lanterns which are technically known as ‘photocytes’. ATP and Oxygen are really attracted to Luciferin but because Luciferin is quite small (only three rings of atoms) it becomes quite ‘energetic’ in the presence of these big guys, and ‘ejects’ its atoms, thereby releasing a whole lot of energy in the form of light. Whilst this is going on, Luciferase (a massive 10,000 atoms) is giving all the chemicals a lovely big hug (in effect the catalyst for the process). Once this is finished the Luciferase lets go of the spent molecules and looks around for some more, and so the process continues over and over again at lightning speed producing that wonderful romantic neon glow!.


Tenuous beetle trivia

Winston Churchill was once reported to state ‘We are all worms. But I believe that I am a glow-worm

When I think of glowworms here is the song that I like to sing along to in my head, or even out loud (simply replace the word ‘flow’ with ‘glow’)



These Bellamy Brothers were definitely singing about glowworms when they wrote these lyrics:


There's a reason for the sunshine in the sky

There's a reason why I'm feelin' so high

Must be the season

When that lovelight shines all around us…


So let your love flow (glow) folks and a Happy St Valentine’s Day from Team Coleoptera! XXX



There’s no greater fun than dressing up as your favourite beetle right?


larviform female glowworm1.jpg

Railroad worm Phrixothrix sp - larviform female! Note Railroad 'worms' also produce a red light on their heads!



We would like to thank Helena for her excellent images and her work volunteering for the Coleoptera section. Here is what she does in the real world!



Member since: Sep 15, 2009

I'm Beulah Garner, one of the curators of Coleoptera in the Entomology department. The Museum's collection of beetles is housed in 22,000 drawers, holding approximately 9,000,000 specimens. This little collection keeps us quite busy!

View Blaps's profile