Forceps of Earwigs 30c 



NOTES ON THE FUNCTION OF THE FORCEPS OF 

 EARWIGS. 



W. p. Morgan, Indiana Central College. 



"Of what use are the pincers?" is a question the writer has been 

 asked many times. Most text-books say they "are either used as claspers 

 in mating or as an aid in folding the wings." This answer seemed 

 inadequate. Last summer at the Indiana University Biological Station 

 observations were made on the use of these "pincers" or forceps. Two 

 large species of earwigs collected in the region of St. Petersburg, Flor- 

 ida, were used (figs. 1 and 2) and an effort was made to secure typical 

 action photographs. This was rather difficult, though, as subdued light 

 was necessary to get the earwigs to react normally, and their move- 

 ments were very rapid. 



The writer recalls that his introduction to the question of the func- 

 tion of the forceps came while making dissections of some Louisiana 

 earwigs. Some of the large insects pinched so vigorously that the 

 points of the forceps nearly pierced the skin. Although the effect of 

 such an attack on a person was of trivial consequences the force would 

 probably have been great enough to crush an insect as large as the ear- 

 wig. Another indication of strength was seen in the large muscles that 

 control the forceps. It seemed unusual that such powerful organs had 

 developed merely as claspers in mating or as aids in folding the wings, 

 especially since many of our earwigs do not fly. Figures 1 and 2 show 

 the powerfully developed forceps in both sexes. 



Another item that early attracted attention was the number of 

 earwigs, especially males, that failed to survive the effect of shipping. 

 The dry forceps of several males and a few females would be found 

 in each shipment (fig. 4). Usually the sexes were separated as soon as 

 unijacked and placed in large mouth bottles. It was from these segre- 

 gated males that the truth of the high fatality of the males during ship- 

 ment was learned to be due to cannibalism. 



The method of attack was always with the forceps and the attack- 

 ing earwig would either flip his body side-ways or run back into his 

 adversary using his forceps all the time in scissor-like strokes. The 

 earwig thus attacked would counter with his forceps and if active and 

 strong enough the battle would I'esolve itself into a sparring match 

 where the forceps were used both as weapons of offense and defense. 

 Not only are the forceps used as pincers but many times the posterior 

 part of the abdomen is raised, lifting the opponent clamped in the for- 

 ceps, entirely off his feet. Occasionally the forceps with their victims 

 are rotated through more than ninety degrees which often permits a 

 more favorable hold beyond the heavily armored abdomen. The ab- 

 domen in all species examined was the largest in the region of the for- 

 ceps and tapered toward the thorax (figs. 1 and 2). As soon as the 

 pincers were clamped on an opponent the earwig would start pulling 

 away as shown in figure 5. This gave protection to its head and 

 thorax and often threw the other insect into a position where another 



"Proc. Ind. Acad. Sci., vol. 33, 1923 (1924)." 



