81 



Luminous Insects. 



By K. G. Blair, B.Sc, F.E.S. Bead 2Ja>j 28th, 1914. 



The power of emitting light at night is a property that has been 

 developed to varying extent in many different branches of the 

 animal kingdom. We find it, for instance, in the Protozoa, e.;/., 

 Noctilitcci, an organism which, though microscopic in size, is some- 

 times present in such countless millions on the surface waters of 

 the ocean as to make the whole sea appear to be ablaze with a pale, 

 cold, " phosphorescent " light. Higher in the animal scale we find 

 the property well developed in the Hydrozoa, e.;/., Pi/rofi»iiia, a 

 colonial oceanic form. We have it again in numerous molluscs, in 

 the insects, and even in the vertebrates, a large number of the fish 

 that inhabit the abysmal depths of ocean, where the sun's rays can 

 never penetrate, carrying their own lamps disposed about their 

 bodies in patterns that vary according to the species. 



To-night, however, I propose to consider only the insects that 

 exhibit this power. 



There is, as might be expected considering the striking nature of 

 the phenomena in question, a very extensive literature on the sub- 

 ject. This is for the most part scattered throughout numerous 

 scientific periodicals, but the earliest part of it, up to 1887, has been 

 collected together by Gadeau de Kerville in his " Insects Phosphor- 

 escents," published in that year. 



It is rather remarkable that the beetles (Coleoptera) have almost 

 a monoply of light emission amongst insects, and even here the pro- 

 perty is almost confined to two families. The first and by far the 

 most important of these for our consideration is the Lampyridae, or, 

 to give them their popular name, the Glow-worms and Fireflies. 

 With them are associated one or two small closely allied families, 

 the Phengodidffi, Rhagophthalmidje, etc., some of which are as yet 

 very imperfectly known and unsatisfactorily characterized. In the 

 Lampyridae proper the luminous organs, when present, are generally 

 found in both sexes, though frequently more strongly developed in 

 one than in the other, and are situated in the terminal or subter- 

 minal segments of the abdomen, the light being shown from the 

 ventral surface. 



All members of this society are familiar with the glow-worm of 

 this country, Lampyris noctiluca. It has frequently been the subject 

 of exhibition at our meetings, and its habits and life-history have 

 recently been illustrated by Mr. Main in his beautiful series of 



