PAN DE AZUCAR 99 



generic groups. These luminous elater beetles are 

 distributed over entire tropical America and are 

 represented by several species. This one is about 

 an inch and a half long and of a black or rusty 

 brown color. Its light is emitted from two oval 

 yellow spots on the prothorax and one beneath ex- 

 tending over a portion of the metathorax and the 

 first abdominal ring. Unlike our northern fireflies 

 this beetle emits a steady continuous greenish light 

 that glows with startling brilliance. The process 

 appears to be wholly voluntary, for if disturbed (or 

 when feeding) the beetle shuts off the light and as 

 suddenly "switches" it on again upon resuming 

 flight. The physiological-chemical reaction in- 

 volved in the production of this light still remains 

 a mystery. Experiments with the bolometer to 

 measure the heat of the glow have given only 

 negative results, although this sensitive instrument 

 responds to the heat of a star. The luminous 

 efficiency of the glow emitted by the beetle is re- 

 markably high — 96%, and is, for its expenditure 

 of energy, actually the most efficient light known. 

 The luminous efficiency of a candle, for instance, 

 is less than one-half of one per cent. — for a tung- 

 sten electric bulb about 4%. Notwithstanding 



