XO. 9 OLFACTORY SENSE OF INSECTS McINDOO 5I 



While experimenting- with odors, it was found that spiders possess 

 a true olfactory sense. Many indivi(hials of two species representing 

 two widely separated genera were used. They responded not only 

 to live ditTerent essential oils, which are sometimes regarded as 

 irritants, but also to both fresh and decayed buttercup flowers, de- 

 cayed snails, squash bugs, and I'halangids. The usual reaction is 

 to move away from the odor, but they also quickly moved their 

 pedipalpi. chelicera and legs, and very often rubbed their legs and 

 other appendages. The average reaction time of a ground spider 

 iLxcosa lepida) to oils of peppermint, thyme and wintergreen was 

 9 seconds and for a jumping spider (Phidippus purpiiratus) 

 4.6 seconds, while for the worker bee the same average is only 2.6 

 seconds. The differences in reaction time may be explained by the 

 fact that Lycosa is rather sluggish, Phidippus is very active, while 

 the bee is extremely lively. However, as a worker bee possesses 500 

 pores more than a spider and since it responds about twice as quickly 

 it would appear that its sense of smell is more highly developed. 



All the lyriform organs (single slits not included) on the legs, 

 pedipalpi, chelicera, mouth parts, and sternum were carefully var- 

 nished with yellow vaseline. The following day they were tested 

 with the five oils — peppermint, thyme, wintergreen, clove and 

 bergamot. Thus it was ascertained that they responded nine times 

 more slowly after varnishing than before. 



Hindle and Merriman (1912) proved experimentally that Haller's 

 organ is olfactory in function and that it is a means by which ticks 

 are able to recognize their hosts. In H cc ma phy salts punctata this 

 organ consists of a minute cavity, containing sensory hairs, and is 

 associated with a specially modified region of the hypodermis. In 

 ticks (Acarina) it is always located on the external dorsal surface 

 of the tarsus of the first pair of legs. Hansen (1893) found a few 

 scattered lyriform organs in acarinids which may also aid in re- 

 ceiving odor stimuli. 



SUMMARY OF AUTHOR'S EXPERIMENTS 



■ The following table is a tabulated summary of the author's experi- 

 ments with spiders and Hymenoptera to determine the location of 

 the olfactory organs. The odors used for the spiders are those from 

 the essential oils of peppermint, thyme, wintergreen, clove, and 

 bergamot. The " three odors " used for the Hymenoptera are those 

 from oil of peppermint, oil of thyme, and oil of wintergreen. The 



