NOTES ON THE EARWIG. 25 



Notes on Early Stages and Life History of the Earwig (Forficula 

 auricularia). {With three plates.) 



By T. A. CHAPMAN, M.D. 



Somewhere about 50 years ago I made some observations on ear- 

 wigs, chiefly to the effect that the mother earwig kept her family at 

 home, and carried in bits of grass and other food for them, and also 

 that the number of joints of the antennae increased as the young ear- 

 wigs moulted. I did not then know that these facts were very 

 imperfectly known and so took no accurate notes. These facts are 

 beiiter known now, but some recent notes on them may not be without 

 value. 



Last year, for the benefit of Lycaena avion, I had some ants nests 

 in observation cases, and for the use of the ants I provided as proven- 

 der, amongst other things, some earwigs. Some of these earwigs 

 remained over, and two of them hollowed out nests and laid eggs, so I 

 proposed to notice how the antennal joints multiplied at each instar. 

 This was not altogether so easy as I imagined, especially as I had a certain 

 amount of fear from some doubtful recollections of my earlier observa- 

 tions that undue interference might make the mother eat or destroy the 

 young earwigs. From time to time I noticed bits of green stuff in the 

 nest that must have been carried in by the parent earwig. The staple 

 food of these earwigs was dandelion, 017 which they got on well enough, 

 but a variation to grass, and especially, when available, to animal food, 

 such as dead msects, seemed always acceptable. I never noticed any 

 insect material carried into the nests. 



The jars were filled about two inches deep with not very damp 

 saud, and on it I laid bits of flat wood and cork, and under these the 

 nests were made, they were simply hollows in the surface of the sand, 

 with the cork as a roof. Naturally, no doubt, a stone usually serves 

 this purpose, but if memory is to be trusted, the nests are perhaps more 

 frequently excavated in the ground simply, deep enough to have a cover 

 of the soil itself. The hollow was not large enough to take the earwig 

 at full length in all its diameters. In one case, my frequent removal 

 of the cover of the nest led the insect to enlarge the hollow obliquely 

 downwards, so that there was not a complete exposure when the cover 

 was removed, but the contents of the nest had a covering of sand, but 

 could be seen imperfectly, by an oblique view. This extension was 

 made whilst there were eggs and growing larvre. 



I did not count the number of eggs, but should guess about thirty, 

 more or less. 



There are six moults, and therefore seven instars, the adult imago 

 being the seventh, or, if we include the egg as an instar, there are 

 eight. 



In the first instar the antenna have eight joints. In the second 

 and third they have ten, in one case there were nine in the second 

 instar. This may have been correct, but I suspect that there is some 

 probability it was the result of injury by its brethren, of this there is a 

 further observation to note. In the fourth and fifth instars the 

 antennal joints are eleven. In the sixth there are twelve, and in the 

 seventh (mature) there are fourteen. Occasionally smaller numbers 

 than these occur, but are almost certainly the result of injury. I have 

 January 15th, 1917. 



