404 



PSYCHE. 



[Aiiifust- -October 1S90. 



An Internal Dipterous Parasite of 

 Spiders. — In the spring of 18S7 while hunt- 

 ing for spiders in company with Mr. G. 

 Dimmock in the cracks on the steep sides of 

 some rocks near Roberts Station in Wal- 

 tham, Mass. I found hanging in cobwebs 

 several soft white maggots and pupae. The 

 webs were generally old and out of repair and 

 a closer examination showed that there were 

 no living spiders in them but in almost 

 every one an empty skin of a common 

 spider, Amaarohius aylvestria, nearly full 

 grown. The skin of the legs and thorax was 

 not clean like a moulted skin but dirty 

 and opaque as though eaten out and the 

 skin of the abdomen when present was torn 

 and shrivelled. From this I concluded that 

 the maggots came out of the spider and 

 from their size must have nearly filled them. 

 The maggots varied considerabl}' in size the 

 largest being a quarter of an inch long while 

 others were not much more than half as 

 large. The hinder half of the body was 

 thicker than the front half and nearly spheri- 

 cal. 



They hung head upward holding to the 

 web by their jaws and were also partly sup- 

 ported by threads under and around them. 

 I was unable that season to raise the adult fly 

 some of the larvae being injured in carrying 

 them home though kept in cobwebs and 

 cotton wool and the others dying apparently 

 from too drvair w'*^hin a few days. In Mav 



1SS9, I again found in the same locality 

 several other specimens also in abandoned 

 cobwebs and with the dead and empty 

 spiders as before and among them one pupa 

 far enough advanced to grow to the adult 

 condition though the skin dried so much 

 that it had to be torn ofl' and the fly never 

 expanded its wings properly. It turned out 



to be a species of Acroccra belonging to a 

 family several species of which have been 

 found parasitic in the same way in spiders. 

 In his monograph of the spiders of Prussia 

 (Schriften der Nat. Gessel. Danzig 1S63-1S66) 

 Menge mentions a similar case. He kept in 

 the house a female Cluhiona put r is in its 

 nest attached to a heath plant. After a 

 few days the spider died and shrivelled 

 and in its place was a maggot suspended 

 by a thin web across the nest. Next day it 

 pupated and a week later there came out the 

 fly, Ho/ofs >ii(ii<ri)i(ifiis Meigen. 



F. Brauer (Verb. d. Zool-bot. -gessel. 

 Wien, 1S69, p. 737) describes Astomella 

 Ihidiiiii Er. , which came from Cieniza 

 aritnia Koch, a trap-door spider from Corfu. 

 The pupa and larva skins were found in 

 the tube and also the dead spider with 

 the abdomen shrunken and having in front 

 a large hole from which the maggots had 

 escaped. 



Both these flies belong to the ticroccridae. 

 My specimen has been examined by S. W. 

 Williston who thinks it is either Acroccra 

 fdsrt'dfa or a species closely related to it. 



y. H. E)iicrtott. 



