Glow Worms: Not Just a Collection of Pretty Twinkling Lights

Female adult glow worms (Lampyris noctiluca) use light to attract a male.

During the First World War, soldiers collected glow worms in bottles and jars to use as lamps in the trenches. Such was the contribution of the glow worms to the war effort, they were commemorated along with many other animals in London at a memorial unveiled by Princess Anne in November 2004.

I’ve been thinking a lot about glow worms recently, about how they might help a lost traveller find their way in the dark for a children’s story I’m working on.  How easy might it be for a bacterium  to take up their ability to glow in the dark?

What came as a surprise was the finding that glow worm larvae feed on snails - they are able to climb up and ride on the larger prey and inject it with venom, usually into the soft flesh of its eyestalk. I think I’ll leave this part out of my children’s story.

The most common glow worm in the UK is Lampyris noctiluca, actually not a worm at all but a beetle. Adult females emit a yellow-green glow at night to attract a mate and this ability of a living organism to produce light is known as bioluminescence. In glow worms, bioluminescence is achieved after a chemical called luciferin first combines with oxygen. The enzyme luciferase then catalyses a reaction producing oxyluciferin and a photon of light. L. noctiluca can’t easily control its supply of oxygen to the reaction, so its light stays on all the time.

This is different from fireflies, which are able to control their oxygen, to flash their lights on and off to communicate with one another. Different species produce different patterns of flashes, meaning one firefly will know whether it’s speaking to another firefly of the same species or not.

In L. noctiluca, all of the eating is done by the larvae - adult glow worms only live for a few weeks to mate before they die - they don’t even have mouthparts! However, this isn’t true for all fireflies. Those in North America belonging to the genus Photuris are often called femme fatale lightning bugs. These fireflies are so good at flashing their light on and off that they are able to mimic the patterns of flashes of other firefly species, to attract their males and, well - to eat them.

So what’s in the glow worm venom that makes them so lethal? Is there anything we can use?

This is a question that has been difficult to answer, since glow worms are so small and they produce their venom in such small amounts. Usual methods to examine such protein soups have needed much larger quantities than it has been possible for glow worms to produce. Until now.

In a recent study, Krämer, Hölker and Predel sellotaped glow worms to a table, gave them a sharp electric shock, and collected the brownish liquid that came out of their mouths. This reminded me of the day when, as a young girl, I wondered how many ants there were in my nan’s garden. I sellotaped each ant I found to a piece of paper in neat columns to ensure I didn’t count them twice. All in the name of Science. (Please don’t do this.)

Many observers have reported that glow worms’ prey appears unable to move after it receives a glow worm’s deadly bite, and so the researchers of the sellotaped glow worm study focussed their search on neurotoxins, toxins that would interfere with the prey’s nervous system and consequently make the organism immobile. You can see how the administration of neurotoxin might be useful for the glow worm to hold down its prey while the digestive enzymes, also present in the venom, get to work liquefying it.

The anticipated collection of digestive enzymes were found in this study - peptidases that chop up lengths of small proteins, glycosidases that break down sugars, and carboxylesterases that digest lots of different types of molecules. As well as these, and in much greater quantities, a number of cysteine-rich peptides were found. Cysteine is referred to as a semi-essential amino acid, meaning it’s not easy for our bodies to make, so it’s important we take it in from our diet. However, cysteine can be toxic in large quantities. All known neurotoxins from all known species contain at least four cysteine amino acids, as was seen for the glow worm peptides.

Now this is the bit I always enjoyed from working with bioinformatics - searching online protein  databases. If you have a protein sequence but you are unsure of the protein’s function, you can compare the sequence to all other reported sequences and see what it is similar to - this can give you a clue. If you’re lucky, your protein sequence will look exactly like another protein that someone else has studied inside and out, leaving you with little legwork to do in the hunt for the protein’s function.

That would be great, but more likely your search - called wonderfully a BLAST search - will return a collection of letters, numbers, perhaps some words and some exotic species names, leaving you with more questions than answers. The search for the identity of the glow worm neurotoxins went something like this.

In essence, seven proteins were found and identified as Lampyristoxin-Ln 1 to 7.

Lampyristoxin-Ln1a-c is similar to a (possible) potassium channel blocker from scorpion venom, as is Ln2 - the protein word used for this neurotoxin was ‘defensin’, which is potentially a progenitor of a scorpion potassium channel blocker - that is to say, the protein is further modified at some point to make a potassium channel blocker.

Lampyristoxin-Ln3 and Ln4 are similar to scoloptoxins from the centipedes Scolopendra morsitans and Ethmostigmus rubripes.

Lampyristoxin-Ln5a and Ln5b are similar to the long neurotoxin OH-34 from Orchesella cincta, a very common springtail in the UK which is not known to be venomous.

Lampyristoxin-Ln6 is similar to a protein called beta-like toxin Tx770, which might affect the inactivation of sodium channels. This protein sequence was found in Buthus occitanus Israelis, the common yellow scorpion.

Lastly, Lampyristoxin-Ln7 is similar to a protein called Asilidin (12)- Dg 3b - nope, no idea on this one either - from Dolopus genitalis… the giant Australian assassin fly. Amazing.

You see? So many more questions than answers.

The adult male ♂ and female ♀ glow worms (Lampyris noctiluca) look very different. The female is much larger than the male, but I have drawn them the same size to show how different they look.

Further Reading

Briggs, H. (2023) The man rescuing Britain’s ‘magical’ glow worms BBC News: Science & Environment. Accessed: 9th October 2024.

Krämer, J., Hölker, P. and Predel, R. (2024) How to Overcome a Snail? Identification of Putative Neurotoxins of Snail-Feeding Firefly Larvae (Coleoptera: Lampyridae, Lampyris noctiluca) Toxins (Basel) 16(6):272.

The Animals in War Memorial, Brook Gate, Park Lane, London W1, UK.