[Reprinted from 'The Zoologist' for May, 1912]
By Richard Elmhirst, F.L.S., Superintendent of the Marine Biological Station, Millport.

On the west side of this Station is a rather marshy field, about three hundred yards long, in which Glowworms are plentiful in some years ; the southern boundary of this field is a road, outside of which is some rough waste ground about a quarter of a mile across, known as Farland Point. The first indication of Lampyris is generally about mid-April, when larvae are found crossing the road; this continues during May, and the majority of such larvae seem to be journeying from the Point to the field.
   In June the female Glowworms begin to shine; towards the end of June the males appear, sometimes in swarms. After mating, the female shines less brightly, and soon disappears. In September larvae are again found on the road, and now the majority seem to head from the field to the Point. A few females may occur quite late in the year; on Nov. 1st, 1908, I found a belated female glowing feebly, the night being mild and close.
   Once a female has been located, she can almost certainly be found at the same spot night after night, until she mates; owing to this habit of taking up a stance the same individual can be kept under nightly observation.
   The real object of these notes is to record the occurrence of the male Glowworms in swarms, and the results of a few experiments carried out during their presence.
   June 26th, 1908. was a bright, hot day, followed by a close evening. On returning home about 11 p.m. I noticed a number of insects outside the window ; in my sitting-room I found over fifty male Glowworms on the table, or hanging listlessly on the walls. On one pane (2 ft. by 3 ft.) of a window facing west I counted exactly sixty. On going into the field I could not see some of the females which I had had under observation for several days, and whose exact locality I knew; however, a pocket electric light revealed them surrounded by often six or more males. The latter shone faintly every now and again, especially when handled. I then put out the lights of the house, and placed on the lawn a red light (photographer’s dark-room lantern), a blue light (a candle in a box behind a sheet of blue glass, such as is generally used in laboratories and museums), and an unprotected candle. The males were attracted in dozens by the red light in whatever position I placed it, but ignored the blue light and white light of the candle. On relighting the gas the diffuse yellowish light at the sitting-room window (blinds cream-coloured) became second favourite to the red lamp on the lawn.
   The following night there was still a considerable number of males about, but in a few days they had all disappeared, except a few which might be found creeping about the females in the field. My nearest neighbour across the field on the west told me he had been bothered for several nights by dozens of flying beetles coming into his house. I counted over one hundred and twenty females in the course of a single evening in the field to the west of the Station.  Yet in the field to the east of the Station, Glowworms were very scarce, three or four at most; this may be due to the presence of hens, or that it is rather further from the Point, which seems to be a wintering ground for the larvae.
   The following summer (1909) I prepared for the appearance of the male Glowworms, and tried them with the red light of a bicycle-lamp; white light of a bicycle-lamp; green light of a bicycle-lamp; blue light of laboratory blue glass; diffuse yellowish white light at window; fluorescent lights got by using screens of (1) fluorescein solution, and (2) 10 per cent. solution of sulphate of quinine.
   On June 23rd Dr. Malcolm Laurie joined me, and showed Finsen rays.  The lights were thrown through paper cones (rather like the horn of a gramophone), which made landing-stages in which insects could be easily detected on arrival, and which only received those coming direct to the light. I discarded these cones, after one trial, as too cumbersome and too easily displaced by the slightest breath of wind. Dr. Laurie kept the Finsen rays in operation from 10.45 p.m. to 1.30 a.m., but, owing to unsuitability of the conditions for handling batteries and generating hydrogen, the current was rather inter­mittent. The only insects which came to the Finsen ray cone were a few small Diptera. This experiment ought certainly to be tried again, and should under favourable conditions succeed in attracting the male Glowworms, since the spectral analyses of Finsen rays and Glowworm light are similar.
   In the course of experiments made daring June 23rd–29th, both in the dark-room and out-of-doors, I found that red was the most attractive colour to male Glowworms; the fluorescein screen and diffuse white light were the next; quinine solution-screen. blue and green, were ignored; bright white light at close quarters was evidently disliked, and markedly avoided. In the field I set up a long strip of canvas on posts; behind this were placed a number of small stands to support the bicycle-lamps or other sources of light.  Within four yards of this canvas screen were seven female Glowworms, five of which remained unmated, after all others which I had located were mated. Several dozen males came close past these females on their way to my red light; the only obvious difference in the conditions surrounding these females being the presence of my experimental lights.
   In 1910 the larvae were late, not appearing on the road until the first week in May; females began to shine about May 20th; by June 16th I had located sixteen, and a few males had appeared. After this I saw practically nothing more of them; possibly a heavy thunderstorm on the evening of June 20th, when 1.18 in. of rain fell in about two hours, may have accounted for this. In 1911 they were very scarce. This year a number of larvae are already about (April 20th).
   In conclusion, the three interesting points are (1) that female Glowworms often take up and occupy a permanent position; (2) that male Glowworms may appear in flights of at least several hundreds; (3) that male Glowworms, like most insects, show a marked preference for red light, which is curious in this particular case. seeing that the light of the female, which should be specially attractive, is at the other end of the spectrum.