ZOOLOGY, ENTOMOLOGY, AND MEDICINE 233 



THE EGG LAYING HABITS OF A PARASITIC DIP- 

 TERON, PTERODONTIA 



By J. L. King, University of Illinois 



The flies of the genus Pterodontia belong to the Dipterous 

 family Cyrtidae. This family consists of a small group of 

 strange appearing flies which are characterized by having very 

 small heads composed almost entirely of eyes, a large hump- 

 backed thorax and inflated abdomen. They are of medium 

 or large size, the species described here varying from 4 to 8 

 mm. in length. 



As far as is known, the larvae live as internal parasites in 

 the bodies of spiders and, according to Brauer, while within the 

 abdomen of the host they breathe by placing their posterior 

 spiracles or breathing tube openings into the lung-chambers 

 of the spider, thus taking their air supply from the lungs of 

 the host. 



The habits of our North American species are but little 

 known and the writer has been unable to find descriptions of 

 the eggs or egg-laying habits of any of our species. In view 

 of this, the following descriptions of the eggs and egg-laying 

 habits of Pterodontia flampes Gray have been prepared : 



On August 7, 1915, the writer, while passing by the border 

 of an open hickory grove, observed several large specimens 

 of Pterodontia flying up and down the trunks of some large 

 hickory trees. The flies were observed for about half an 

 hour ; during this period they continued to hover up and down 

 the tree trunks from about a foot above the ground to a height 

 of ten to fifteen feet. They flew on the leeward side of the 

 trunks and from one to two inches away from the surface of 

 the bark, and at such times they were so sluggish that it was 

 possible to pick them up in one's fingers, and if allowed to 

 escape they immediately resumed their hovering flight up and 

 down the tree trunk. In fact, they may be pierced through the 

 thorax with a common pin and if released show no particular 

 injury or fright, but continue their hovering flight as before. 



Before leaving the locality one of the flies was taken alive 

 and carried in a handkerchief. Upon returning to my field 

 laboratory and transferring the specimen to a bell-jar, it was 



