Sept., I9I2.] Knab: Diptera at Home on Spiders' Webs. 145 



1906 Coqiiillettomyia dentata Felt was observed in numbers on cob- 

 webs at Newport, New York. 



A record of similar habits comes from Australia. Skuse, in the 

 introductory part of his treatment of the Cecidomyidse, speaks of the 

 images frequenting spider webs " sometimes in tens of thousands."^ 

 Apparently he was under the impression that the habit is general 

 within the family, for no genera or species are mentioned. My own 

 observations lead me to believe that the habit is restricted to certain 

 genera, possibly to certain species of these genera. Dr. Felt in- 

 forms me that Kieffer has recorded at least one species of Cecido- 

 myidse as found on spider webs in Europe, but I have not had the 

 necessary time to search the numerous writings of this author for 

 the record. 



In September, 1910, I was surprised to find Diptera of still an- 

 other family frequenting a spider's web. The web was a large 

 " orb web " of an epeirid, known to be particularly fatal to insects, 

 and was in an exposed situation at the margin of a stream. Upon 

 the threads of this web sat a number of small flies, which, on being 

 frightened, flew off but promptly returned to the web. These flies 

 proved to be Chironomidse and are an apparently undescribed species 

 of the genus Bezzia. It would seem that in this case there is an ob- 

 vious reason for the presence of the flies on the web. They are in 

 all probability mess-mates of the spider. There are a considerable 

 number of observations which show that certain species of the group 

 to which the present insect belongs (Ceratopogonins) suck the juices 

 of other insects. In the present case the prey of the spider no doubt 

 furnishes a convenient source of food for the flies. The fact that all 

 six of the specimens captured from the web are females supports this 

 view. 



In a recent paper on East Indian Tipulidae, by De Meijere, ob- 

 servations made in Java by Doleschall and by Jacobson are given 

 which show that at least two species of Limnobiinae habitually sus- 

 pend themselves from horizontal spider threads and by this means 

 perform a curious dance." 



One of these species is Dicranomyia saltcns Dol., the other Mon- 

 gorna pcnnipes O. S. With reference to the first, which is abundant 



^ Proc. Linn. Soc. N. S. Wales. 2 sen, Vol. 3, p. 52 (1889). 

 "Tijdschr. v. Ent., Vol. 54, p. 22-22, 50-51 (ipn)- 



