Nocturnal Insects: A Guide to Night-Flying Species
When the sun sets, a hidden world of insect activity comes alive. While daytime insects like butterflies and bees receive most of our attention, the night shift is every bit as diverse and fascinating. Moths alone outnumber butterflies in Britain by roughly 40 to 1, and many beetles, flies, lacewings, and other groups are primarily or exclusively nocturnal. This guide introduces you to the most important night-flying insects in the UK and provides practical advice for observing them.
Why Do Insects Fly at Night?
Nocturnal activity offers several advantages:
- Reduced predation – Many visual predators (birds, dragonflies) are inactive at night, reducing the risk of being caught.
- Less competition – Night-flying pollinators face less competition for nectar from daytime visitors.
- Lower temperatures – Night flying avoids the desiccation risk of hot daytime conditions, particularly for small-bodied insects.
- Humidity – Higher nocturnal humidity benefits insects that are prone to water loss.
- Scent dispersal – Cooler, calmer night air can carry pheromone signals over greater distances, aiding mate location.
Navigation at Night
Nocturnal insects navigate using a variety of cues, including moonlight, starlight, the Earth's magnetic field, and polarised light patterns in the night sky. The well-known attraction of moths to artificial lights is thought to result from transverse orientation—a navigation strategy in which insects maintain a fixed angle to a distant light source (the moon). When the light source is nearby (a lamp), maintaining a fixed angle causes the insect to spiral inward towards it.
Major Groups of Nocturnal Insects
Moths (Lepidoptera)
Moths are the quintessential nocturnal insects. Of the approximately 2,500 moth species in the UK, the vast majority are active after dark. Highlights include:
| Species | Wingspan | Flight Period | Notable Feature |
|---|---|---|---|
| Elephant hawk-moth (Deilephila elpenor) | 45–60 mm | May–July | Stunning pink and olive colouration |
| Poplar hawk-moth (Laothoe populi) | 65–90 mm | May–August | UK's most common hawk-moth |
| Large yellow underwing (Noctua pronuba) | 50–60 mm | June–October | Britain's most abundant moth |
| Peppered moth (Biston betularia) | 35–60 mm | May–August | Famous evolution case study |
| Garden tiger (Arctia caja) | 45–65 mm | July–August | Bold orange and black warning colours |
| Privet hawk-moth (Sphinx ligustri) | 80–120 mm | June–July | One of Britain's largest moths |
Beetles (Coleoptera)
Many beetle species are nocturnal, spending the day hidden beneath bark, stones, or leaf litter and emerging at night to feed, mate, or disperse:
- Stag beetles (Lucanus cervus) – Males fly on warm summer evenings in search of females, and their buzzing flight is a spectacular sight in southern England.
- Cockchafers (Melolontha melolontha) – Also called May bugs, these large beetles fly clumsily around lights and trees on warm May evenings.
- Glow-worms (Lampyris noctiluca) – The wingless female glows on warm June and July evenings to attract flying males.
- Ground beetles (Carabidae) – Many species, including the violet ground beetle (Carabus violaceus), are primarily nocturnal predators.
Other Nocturnal Insects
- Lacewings – Green and brown lacewings are often attracted to lit windows on summer nights.
- Caddisflies – Adult caddisflies are largely nocturnal and are frequently found at light traps near rivers and streams.
- Crane flies – Many species are crepuscular or nocturnal, particularly active around dusk and dawn.
- Mosquitoes and midges – Peak activity occurs at dawn and dusk (crepuscular) or throughout the night.
- Earwigs – Almost entirely nocturnal, hiding in crevices during the day.
Did you know? The death's-head hawk-moth (Acherontia atropos), famous for the skull-like pattern on its thorax, is one of the few moths capable of producing audible sounds. It can squeak loudly when disturbed and is known to enter beehives at night to steal honey, producing a calming scent that prevents the bees from attacking.
How to Observe Nocturnal Insects
Moth Trapping
The most popular method for studying nocturnal moths is light trapping. Several trap designs are commonly used:
1. Robinson trap – A bucket-shaped trap with a powerful mercury vapour (MV) light. The most effective design, attracting moths from a wide area. Best for serious recording.
2. Skinner trap – A flat, portable design with Perspex baffles that guide moths into a box. Easier to transport than a Robinson trap and still highly effective.
3. Heath trap – A small, lightweight trap using an actinic (UV) tube. Less powerful but battery-operated and ideal for fieldwork in locations without mains electricity.
4. Wine roping – Ropes soaked in a mixture of red wine, sugar, and overripe fruit are hung from branches. Moths are attracted by the scent and can be observed feeding.
5. Sugaring – A thick paste of treacle, brown sugar, and beer is painted onto tree trunks and fence posts at dusk. This traditional method can attract species rarely caught at light.
Tips for Nighttime Insect Watching
- Choose warm, calm, overcast nights – These conditions produce the best moth activity. Cold, windy, or brightly moonlit nights tend to be poor.
- Use a red torch – Red light is less disruptive to nocturnal insects than white light. A head torch with a red filter allows you to observe without disturbing your subjects.
- Check outside lights – Porch lights, security lights, and illuminated windows attract a variety of nocturnal insects. A morning check of window sills can reveal moths that arrived overnight.
- Plant night-scented flowers – Honeysuckle, night-scented stock, and jasmine attract nocturnal pollinators.
- Record your findings – Submit moth records to your county moth recorder or the National Moth Recording Scheme.
Key Takeaway
The night-time insect world is rich, diverse, and largely unexplored by most people. Moths dominate the nocturnal sky, but beetles, lacewings, caddisflies, and many other groups are also active after dark. Light trapping, sugaring, and simply checking outside lights are accessible and rewarding ways to discover this hidden world. With Britain's 2,500+ moth species alone, nocturnal insect watching offers a lifetime of discovery.