Lampyris noctiluca a.k.a Common Glow-worm

Taxonomy

• KINGDOM  –  ANIMALIA
• PHYLUM  –    INSECTA
• CLASS  –  COLEOPTERA (otherwise known as beetles) not worms!
• FAMILY – LAMPYRIDAE (Fireflies)
• GENUS – LAMPYRIS (genus of Fireflies that most European species belong to)
• SPECIES – Lampyris noctiluca  

Description and life cycle

Larval stage (juvenile)

I think they look a bit prehistoric. A segmented dark body with pale spots at the rear edge of its individual segments. Wingless. Three pairs of jointed legs. Not exactly the fastest thing you’ll ever see but a determined mover with caterpillar like action. Curved pointed mandibles. Can sometimes be confused for Ladybird larvae.

Back to those mandibles. Larvae are ferocious predators of snails and slugs. Those mandibles are used to nip at the flesh and inject a toxic substance that paralyses the prey and liquifies the flesh. The larvae lap up the liquified flesh, snail soup anyone? Eating snails is a messy affair but the larva has a handy attachment on its tail of hooked bristles which it uses to wipe its mouth.

Hatching around 45 days from eggs laid in the vegetation or under rocks/logs or soil during the Summer the larvae can spend two or three years as a juvenile going through several moults as they grow, each period in between moults known as instars. During Winter they hibernate as prey becomes less available.

Both sexes of larvae are capable of glowing. Slow flashes are produced, one potential reason being to ward off predators although as larva and adults are in themselves toxic, they are not generally predated upon.

In the Spring of their 2^nd or possibly 3^rd year they go on the march looking for a suitable pupating spot, pupate and emerge as adults.

Adults

Adults are sexually dimorphic, meaning males and females are very different to each other. Males are recognisable as beetles with elytra (the hard wing cases that protect the delicate wings). Males are smaller than females with huge eyes and a distinctive ‘hood’ over them, thought to protect the eyes. Males are capable of glowing but it is rarely observed and only faint.

His large eyes are adapted for low light conditions to detect the displaying females.

Females are a lot larger than males and are larviform, that is they still resemble the larva. Not being winged they are flightless.  She displays her yellowy green bioluminescence from her last three segments. Two segments are solidly lit while the last is just two small spots of light.

If she reads the textbook (see below for ‘Scottish Glow-worms may not read textbooks’) she will climb a short height up vegetation and clinging onto it will turn on her lantern sometimes slowly waving her abdomen, so it appears as a slow blink or flash and presumably to direct the light in all directions. Known as sexual signalling this is her way of displaying to the low flying males that she is available for mating. Once a male has detected her and they have mated she will descend to the ground, turn off her lantern and lay her eggs. Got the tissues handy? Because here’s the sad bit.

Neither sex as adults are capable of feeding. All the hard work of predating molluscs during the larval stage is in preparation for adulthood. Energy stores built up as a larva must sustain them through pupation, mating and egg production. After mating both sexes succumb to starvation and perish. Females glow every night for a few hours up to 10 nights until she is either mated or if remaining unmated expels unfertilised eggs.

Producing that bioluminescence must be costly in terms of energy depletion, right? Wrong, here comes the science bit!

Bioluminescence is a cold light that is in fact a chemical reaction. Please excuse the following layman description if you are a chemist or expert!

The abdomen contains an organ commonly known as a lantern. Within the lantern there are two molecules Luciferin and an enzyme called Luciferase. In the presence of oxygen and ATP the chemical reaction produces a cold light that is energy efficient. If chemistry is of interest, I highly recommend reading the published paper in the publications tab. Basically, that chemical reaction costs the Glow-worm very little in terms of energy loss. If you touched the lit segments, you would not feel any heat. So, our wee female can use her energy stores to produce eggs.

Her glow is quite bright, think of a small LED diode kind of light. However, it is not always easy to see in amongst vegetation and you can (and I do) walk right by a glowing female having not noticed her. Larvae are more difficult to see. Only twice have I seen a larva up here and that was only because my eagle eyed partner spotted them. Males are even more difficult to see unless you happen across a mating pair.

Scottish Glow-worms may not read their textbooks.

In the time I have been studying this species I generally find them glowing at ground level. So far I have seen very few climb vegetation/exposed rocks or logs at any height to display from. In fact, most of the time I find them glowing under vegetation or even recently mown grass. This is contrary to how they should mostly behave. It is making my job as a researcher far more difficult to find them!

Sometimes they are rebels when it comes to temperature too. Witnessing glowing females when the air temperature is a relatively chilly 7degrees Celsius seems to be contradictory to populations south of the border that prefer higher temperatures i.e. above 10 degrees.

Don’t get me wrong we do have night-time temperatures above a balmy 10 degrees during the Summer but up here lower temperatures are not uncommon. I have been kicking myself for not wearing warmer clothing while observing glowing females who are determined to continue displaying despite a sharp drop in temperature.

Take a look at the research tab to see how I am going to try and quantify both of these casual observations into a dissertation with the possibility of further research during my time as a student.

What time of year is ‘glowing season’

In the UK the glowing season can start between late May and continue through to July or sometimes even August but generally in Scotland it is between late May and June.

Females begin to glow at about the time we can no longer make out colour as night falls. In Scotland that can be as late as 11.30pm! Many a time I have been impatiently waiting for darkness to fall as our more Northerly position means we have less hours of darkness during the Summer.

I have been privileged to observe a glowing female no more than a metre from me in my tent who lit up her lantern at about 11.30pm until well after 1am close to breakwaters on a rocky coastline. Sadly, she remained unmated that night and I didn’t repeat the survey the next night so do not know if she was mated eventually.

Up here I have observed them glowing anywhere between about 10.30pm until 2am.

Habitat

It is sometimes said they prefer calcareous grassland but as acknowledged on the brilliant site created by Robin Scagell at https://glowworms.org.uk/#About%20glow%20worms Glow-worms can be found on many different types of sites.

Criteria that as a rule applies are

• Grassland/scrub that is unimproved or at the very least semi improved. Not a species that tolerates pesticide or fertiliser use.
• Damp areas
• Dark skies, that is no direct light pollution from streetlights for example.
• Good prey populations

So that leaves us with a wide variety of potential sites. In Scotland, the populations we know about live on unlit road verges, grassland on marginal/hill sheep farms, forestry rides, coastal, railway embankments and areas close to them.

There really is no typical habitat so anywhere that fits the above vital criteria could have a Glow-worm population.

Does the weather affect them?

Yes. A blowy night with heavy rain will deter them from displaying as well as restrict the males flying. Light rain does not appear to affect them. The effect that temperature has on them is one I am researching. A balmy still humid night is perfect conditions for displaying and will give the best chance to see them. I have yet to see displaying behaviour being affected by moon phases or cloud cover.

The bad news.

We know in England that they are declining. Impact on populations include pesticide use, another good reason to bin those slug pellets! Intensive agriculture, habitat loss and artificial lights (streetlights, garden lighting, vehicle headlights).

Artificial light has a negative impact on the ability of the males to locate displaying females leading to females being unmated. Studies conducted in Finland have shown females also respond to artificial light in a negative way by turning their lantern off if exposed to that light for 45minutes. In their experiments the females did not resume glowing after the light was switched off. For alarming reads please see the links section for published papers relating to artificial light impacting on Fireflies and other nocturnal insects.

Habitats in England are a rare commodity. We require housing, roads and developments to work, shop and spend leisure time. This will, of course impact on sites that have populations of Glow-worms.

My main research site is close to a motorway junction that was developed on ground that had known populations. They disappeared from that site and as yet I do not know if my site, a mile or two away is connected to that historical population.

Glow-worms are not protected and not considered during environmental impact assessments or planning processes.

So how can Scotland help and contribute to the overall data for the UK?

Scotland is very unrecorded. Is that because we only have a few fragmented populations that are already known? It is more likely we do have far more of a population than is currently known.

Most of my time late May until the end of June is spent travelling around surveying potential sites, revisiting historical sites or studying my main research site.

Very few people know the UK has a Firefly species, even less so in Scotland. When I talk to people about them, I am often greeted with exclamations of surprise. ‘Fireflies are in the warmer countries surely?’ is a common response. Think of Fireflies and I bet we all immediately think of the tropical regions or America.

Then there are the problems of looking for them. Firstly, there is not exactly an army of people willing to walk sites at night without the aid of torchlight. It is not among the common wildlife watching activities to participate in.

Folk who are likely to be out watching wildlife at night are generally into the more well known nocturnal creatures such as Bats, Badgers and Owls. Even as an avid moth trapper it is not necessary to sit with the light trap through the night. I can sleep soundly while the moths are attracted to the light trap and settle in the collecting box until dawn when I can then appraise my catch and release the moths unharmed into vegetation in the light. A simple lack of people out at night means the Glow-worms are not likely to be seen by human eyes.

Casual observations do come to me from gamekeepers, farmers and foresters as well as older folk who fondly remember holidays or nights out involving nice country pubs then staggering home worse for wear and thought they were so drunk they were seeing things! These sightings never get recorded. A small number of records do come in each year from chance encounters or from one of a handful of people who do go and look in there local area and conduct a count.

Next is the needle in the haystack problem. Scotland is not a large country but what we lack in overall land mass we more than make up for in percentage of land that falls into the vital requirements category, that is undisturbed with less impact from humans.

In short there is vast areas of potential with very few pairs of human eyes to observe these magnificent creatures. We just don’t know where they are.

Knowing where they are and on what habitats could reveal that Scotland has a thriving population and could act as a reservoir for the species in the future. Although it could also be that our populations are in trouble and need help. Either way it is only by finding and recording them that data can be gathered to determine their status here.

Why do they matter?

I could just say ‘it’s a Firefly, what’s not to love’ but I’m biased so that doesn’t quite cut it.

For a start the world of the invertebrates is in trouble. Declines globally across the taxa are alarming. We are losing species range and abundance that has been mostly caused by our actions. Invertebrates are going extinct before we even know anything about them.

If they die, we die. It really is that simple. Without invertebrates we cannot survive for long. Relying on them for food production is the main reason we need them.

Invertebrates are providers of ecosystem services, in plain terms they provide us with services that we would otherwise have to pay unimaginable amounts of money for.

Invertebrates are part of the engine that drives ecosystems. Towards the bottom of the food chain they are the food source for a wealth of other animals that us humans enjoying sharing the planet with.

Invertebrates act as the proverbial ‘canary in the mine’. Vulnerable to environmental changes such as pollution they inform us of the health of the planet.

Apart from all of that there is this consideration. Bees and Butterflies are commonly used as a tool to get people interested in the conservation of invertebrates. They are the ones not usually aversely viewed by us. We see them as the friendly ‘creepy crawlies’.  Glow-worms, as with the Fireflies of warmer climes are a welcome addition to the arsenal of these positively viewed insects. I challenge anyone not to be charmed by the sight of a glowing female and subsequently endeavour to think more about the impact we are having.

Some English sites conduct public Glow-worm walks where people can pay a small fee to have an escorted group walk to view glowing females. Welcome revenue for sites that rely on donations to operate. Scotland is famous for its wildlife. Golden Eagles, Red Deer, Atlantic salmon, Red Grouse, Otter and marine mammals amongst some of the iconic animals that call Scotland home and provide much needed revenue in rural areas. I know I am obsessed but as an ex shepherd who has witnessed most of what Scottish wildlife has to offer seeing a female glowing is every bit, if not more special.