Mercury – the winged messenger of the nocturnal gods
I’m well into my ninth season of garden moth trapping, which basically involves enticing moths into the garden using an ultraviolet lamp, hoping they will settle on the egg trays in the trap that act as roosting spots for them overnight, and then identifying, counting, and photographing them in the morning, before letting them back into the wild unharmed.
I’ve used various ultraviolet (UV) lamps over the years, largely fluorescent tubes and a LepiLED. I have now purchased an 80W mercury vapour (MV) bulb and the associated electrical gubbins to use it. It’s a very much brighter source with a more intense UV emission than any fluorescent tube or even the LED. It should attract more moths of a wider diversity. We’ll see.
If I remember rightly, the actinic fluorescent tubes I’ve used in the past have their emission in the UV-A at 365 nanometres. Synergetic tubes have an additional emission peak, while the LED is in the UV as well as being bright in the blue and green of visible light. The new 80W MV lamp has emission profile something like that in the table, where the wavelength mentioned is the peak of the band covering that region of the electromagnetic spectrum:
| 253.7 | UV-C | Blocked | Outer borosilicate glass blocks this; inside quartz arc tube, it excites the phosphor coating |
| 313.2 | UV-B | Trace | Small leakage through glass; mostly blocked |
| 334.1 | UV-A | Low | Minor mercury line; partially passes through glass |
| 365.0 | UV-A | High | Dominant “I-line” attracts insects; passes easily through glass |
| 404.7 | Visible | Moderate | Deep violet |
| 435.8 | Visible | Strong | Blue/violet; one of the strongest mercury lines |
| 546.1 | Visible | Very Strong | Green; contributes heavily to human-perceived brightness (Lumen output) |
| 578.0 | Visible | Strong | Yellow; significant for colour rendering |
| 600-700 | Visible | Moderate | Red emission from phosphor coating; fills in the “red gap” making the lamp appear bright white |
I have high hopes for this new lamp. I’ve already recorded over 570 species of moth in my garden (336 of which are macro moths as opposed to micro moths). But, there are so many more to see. There are some 2500 macro and micro moths in the UK. Details and full list of species via the mothing link.
With the old actinics and LED lamps my per mothing session averages are usually around 50-60 specimens. Even with moth declines over the last few years, I anticipate getting more specimens and greater diversity once we’re into the peak summer season.
I will probably set up a standalone spreadsheet for the lighting-up sessions where I use the MV (which may well be just weekly) and keep the old trapping spreadsheet for the more frequent actinic sessions.