THE BEETLES: COLEOPTERA 



43 



luminous insect, though it is not given off when the insect is 

 at rest or feeding. 



Fireflies. The power of giving off light is possessed by 

 the majority of the members of an allied group, the fireflies 

 (Photu'ris, Fig. 26), soft-bodied insects about two or three 

 centimeters in length, dull-colored, and with the prothorax 

 usually margined with red or yellow. The wing-covers are 

 much softer than in other 

 beetles. Fireflies are, for 

 the most part, nocturnal 

 in their habits, clinging 

 to the under side of leaves 

 during the day. They are 

 protected from the insect- 

 eating birds by a strong 

 odor which renders them 

 distasteful. The lumi- 

 nous spots are on various 

 abdominal somites, gen- 

 erally the last. Fireflies 

 appear in greatest num- 

 bers in the latitude of 

 the Middle Atlantic states 

 for a week or more in the 

 month of June. Many 

 attempts have been made 

 to account for the light 

 produced by the fireflies. 

 The light-giving organ 

 seems to consist of fat- 

 cells inclosed in a network of fine tracheae. These cells 

 apparently have the power, under nervous control, of secret- 

 ing a substance, possibly phosphureted hydrogen, which is 

 luminous when acted upon by the oxygen furnished by the 



FIG. 26. Firefly. Slightly enlarged 



