Light trapping

Light trapping insects using light traps

Shedding Light on the Dark: Scientific Light Trapping and the Hidden World of Moths

When the sun goes down, most nature photographers pack up their cameras. But for entomologists (insect researchers), the most exciting time is just beginning. Scientific "light trapping" is the most effective method for inventorying the biodiversity of a habitat. But how exactly does it work, and why is it more important than ever?

The Physics of Attraction: Which Wavelengths?

Insects see the world differently than we do. While humans react to the visible spectrum (red to violet), the eyes of most nocturnal insects are extremely sensitive to short-wave light, particularly in the ultraviolet range (UV).

• The Sweet Spot: The most effective wavelength lies between 360 and 390 nanometers (UV-A). To the human eye, this light is barely visible ("black light"), but for insects, it shines like a beacon.

• Visible Light: Often, a portion of blue or green light is added to broaden the spectrum, as different species react to different wavelengths.

The Equipment: The Mobile Laboratory

In the past, heavy generators and hot mercury vapor lamps were used. Today, the technology is lighter and more efficient:

1. The Light Tower or Light Sheet: The centerpiece is a white surface that reflects the UV light. A Light Tower is a cylindrical tube made of white gauze (mesh fabric) with the lamp hanging in the center. A Light Sheet is stretched vertically. Insects fly towards the light and settle on the fabric.

2. The Light Source: Modern high-power LED systems (such as the LepiLED) are the standard today. They are lightweight, powered by power banks, and cover exactly the required wavelengths.

3. Camera Setup: Since we want to document rather than collect, a camera with a macro lens is essential. An external flash with a strong diffuser is mandatory to soften the harsh light and capture the fine scales of the moths without overexposure.

Who Comes to the Light?

Although we usually talk about "moths," the audience at the light trap is diverse:

• Moths: They make up the majority of visitors. From tiny micromoths to giant hawk moths.

• Beetles: Longhorn beetles, ground beetles, and scarab beetles.

• Other Orders: Caddisflies, lacewings, and cicadas.

Butterflies vs. Moths: The Austrian Statistics

Here it becomes clear why nocturnal research is so important. Many people think of colorful butterflies when they hear "Lepidoptera," but that is just the tip of the iceberg.

The numbers for Austria are impressive:

• Butterflies: There are only approx. 215 species.

• Moths: There are nearly 4,000 species.

This means: Over 95% of our butterfly and moth diversity is nocturnal. Anyone who only researches during the day is ignoring almost the entire order of Lepidoptera. Moths are essential pollinators and a crucial food source for bats and birds.

Documentation Instead of Collection: The Photographic Approach

Historically, it was common to kill and pin moths to identify them. For many scientific purposes (genital examination in very similar species), this is sometimes still necessary, but for monitoring, the trend is strongly moving towards photographic voucher collections.

The Workflow:

1. The insect lands on the light sheet.

2. You take a high-resolution photo (the camera sensor should be exactly parallel to the wing to maximize depth of field).

3. The photo is uploaded to platforms like iNaturalist or Observation.org.

These "Citizen Science" data are gold for research. They help create distribution maps and document changes caused by climate change. see Blogpost Citizen Science

New Discoveries in Austria: An Unfinished Book

One might think that everything is known in a well-researched country like Austria. Far from it.

In recent decades, dozens of new moth species have still been recorded in Austria. This happens in two ways:

1. True New Findings: Species extending their range northward due to global warming (e.g., from the Mediterranean region).

2. Cryptic Species: Through DNA barcoding, it is discovered that what was thought to be one species for 100 years is actually two genetically distinct species that look almost identical.

Moth research is therefore not just an inventory of the past, but an active voyage of discovery in one's own country.

My Documentary Night Shots:

A Selection

Light trapping at night offers great opportunities for macro photographers

Beyond purely documentary shots, night sessions offer macro photographers many great opportunities to capture fantastic images. Here is a selection of my night shots:

Sometimes, on the way home from a night session, you might even encounter other, larger animals—ranging from bats to wild boars. For instance, I once ran into this very curious stone marten at 3:00 AM:

I am already looking forward to future night sessions, especially during the mild summer nights near Vienna.