412 



NATURE 



[December 9, 19 15 



will remind you that in this species, in the adult stage, 

 the light-giving property is practically confined to the 

 female. Destitute of wings, she is rather an unlovely 

 object, doomed to crawl about amongst the grass and 

 low herbage, while her prospective spouse enjoys 

 the freedom of the air above her. Yet her light is 

 emitted from the underside of her tail, a situation that 

 would not at first sight appear to be particularly well 

 chosen as a source of illumination. Her modus 

 operandi in exhibiting her light is usually to climb a 

 little way up some convenient stem and to sit there 

 with her lamp suspended, her body twisted a little to 

 one side so as to exhibit the light without obstruction. 

 If she can find no stem stiff enough to bear her weight 

 she will remain with her body on the ground, the 

 abdomen twisted to one side to expose the light as 

 freely as possible, turning it first to one side then to 

 the other in her attempts to attract the attention of 

 wandering males. At Lugano Mr. H. Main and I 

 have observed that they were particularly partial to old 

 walls, even sitting lo or 12 ft. above the ground. 

 Though we found the larvae fairly plentiful in the 

 grass the female beetles were always on the walls, 

 and in such a situation their light was plainly visible 

 from a long distance; the twisting motion of the 

 abdomen was also clearly observed. 



Luminous organs are present in the male glow- 

 worm in a similar situation, but to a very minor 

 degree. The extent to which they are functional 

 possibly varies in different localities. It is probable 

 that in this sex the light is emitted only for a com- 

 paratively short time after reaching maturity, and that 

 it soon becomes exhausted. 



Photogenic organs are also present in an advanced 

 degree in both the larva and the pupa; even the eggs 

 are luminous, though there is here no definite light 

 organ, but the whole surface glows faintly. 



To the same family belong the "fireflies" of 

 southern Europe. Of these there is a considerable 

 number of species, which possibly present slight differ- 

 ences in the details of their lip-ht emission. One of 

 the best known is Luciola italica of northern Italy, 

 a species the habits of which Mr. Main and I had 

 the pleasure of studying at Lugano. 



Luciola italica was observed on the evening of our 

 arrival at Lugano, ifi the grounds of the school, near 

 the lake. Though abundant after dark, thev were 

 scarcely to be observed during the day. The first 

 flashes were seen about 8.30, while the lingering 

 daylight was fairly strong, and they were most 

 numerous about q.30 or 10, after which time their 

 numbers noticeably decreased, though they could still 

 be seen from our bedroom windows well after 11 p.m. 



As was to be expected, all the fireflies caught on 

 the wing were males. They have a fairly steady, not 

 very rapid, flight, and flash their lig-ht at almost 

 regular intervals, but they do not obviously appear 

 to he searching for the females. When they do per- 

 ceive an answering flash — and the discovery seems to 

 be a matter of accident rather than the result of 

 deliberate search— they pause in their course, and then 

 fly down to it, although they may be as much as 

 10 ft. away. 



The females were never observed to use their wings, 

 but were always found on the grass or the herbage. 

 In these insects, unlike the American Photuris, etc., 

 observed two years ago, the initiative in seeking- a 

 mate appears to be with the female, as in the case 

 of Lampyris. At times they will be quite dark, while 

 sometimes they will glow with an almost steady, 

 though not very bright, light. When "calling" for a 

 mate, however, they flash with rather long slow 

 flashes, incompletely extinguished in the intervals. 

 NO. 2406, VOL. 96] 



Such a period of flasliing is usually of short duration, 

 and is succeeded by a dark period. It is this suc- 

 cession of slow flashes that bears the appearance of 

 definitely calling for a mate, and during which the males 

 most readily approach her, though they are also 

 attracted to some extent by a steady glow. 



The males, both in captivity and in nature, i.e. 

 when caught in a spider's web, were observed to glow 

 with a constant though not very brilliant light, some- 

 what resembling- the steady light of a female, but 

 no case of flying males approaching these dead males 

 was observed. 



The mating habits of many American species of 

 Lampyridae, popularly known as lightning-bugs, have 

 been investigated recently by McDermott.^ In these 

 insects, as in the European Luciola, both sexes are 

 luminous, and the light is emitted as a series of 

 coruscating flashes. Again, the male has the more 

 brilliant light, but in these insects he seems to take 

 the initiative in searching for a mate, hovering over 

 the ground flashing his lamp, and apparently watching 

 for an answering flash from the less active female 

 concealed in the grass. 



The lightning-bugs investigated by McDermott 

 belong mainly to the genus Photinus, of which the 

 species are numerous, two or more of them often 

 being found on the same ground. The results of this 

 investigator's observations, assisted by a series of 

 ingenious experiments with small electric bulbs which 

 could be operated to simulate the flash of the insect, 

 conclusively show that each species has its character- 

 istic method of exhibiting its light, and that an indi- 

 vidual of any one species Will in general only reply 

 to, or evoke a reply from, a member of the opposite 

 sex of that species. He found, however, that some 

 species would respond much more readily to his arti- 

 ficial flashes than others, and that some would even 

 answer the flash of a match. 



A few details of his observations on certain species 

 may perhaps be quoted :- — 



Photinus pyralis. — The flash of the female is given 

 three or four seconds after that of the male, and is 

 of the same colour, but of longer duration and less 

 intense. 



Females would answer in numbers to the flash of 

 a match swung in an arc to simulate the flash of a 

 male, though as a rule not more than one female 

 would reply to a flashing male. 



A particular female would not reply to the flash of 

 a male of another species (P. consanguineus) though 

 she would to that of a match. 



The male could also be deceived by a bulb placed in 

 the grass and flashed three to five seconds after his 

 own flash; when the bulb was flashed without the 

 pause it was not so efl"ective. 



No male was ever observed to reply to the flash of 

 a creeping male. 



P. consanguineus. — The male gives a double flash, 

 two flashes in quick succession followed by a pause, 

 then two more, and so on : the female replies within 

 a second^ to the second flash of the male. 



A particular female would not reply to the flash of a 

 match, but would answer the double flash of a bulb 

 when 20 or 30 ft. away ; on a nearer approach she 

 seemed to recognise something unusual and would no 

 longer replv. 



P. scintillans.— The ms\c gives a short single flash 

 and the fern ale a longer single flash; the female in 

 this species is apterous. 



A female would replv to the first flash of a male of 

 P. consanguineus, but the latter takes no notice. 



P. marginellus. — ^The male gives" a single short sharp 



" Canad. Entom.^ '910, pp. 3 = 7-363; 1911, pp. 399-406; igia, p. 73 and 

 PP- 309-312. 



