CADDIS-WORMS AS AGENTS IN DISTRIBUTION 

 OF FRESH WATER SPONGES. 



Frederic H. Krecker. 



A freshwater sponge, which is probably Spongilla fragilis, 

 is found in great abundance on the rocks and other sohd objects 

 in the region of the Bass Islands, Lake Erie. It is a green 

 sponge which usually grows as a delicate incrustation on the 

 objects to which it is attached; at times it assumes a cylindrical 

 shape. While examining some material which had been 

 dredged from what is known as Gibraltar Bar in Put-in-Bay, I 

 noticed that the cases of a caddis-fly larva belonging to the 

 RhyacophilidcB were covered by Spotigilla. The dredging had 

 been done in five feet of water on a stony bottom. 



The case of these Rhyacophilidce is made of a parchment-like 

 material in the form of a cone approximately 12 millimeters 

 long. The broad end has an opening through which the larva 

 is able to protrude its body and crawl about with its case. 

 The cases examined were encrusted to a varying extent 

 by the sponge. Several were entirely covered except for a 

 small patch on the ventral side near the opening. On other 

 cases merely a small spot was occupied. Between these 

 extremes there were cases showing all intermediate stages. 

 Professor Stephen R. Williams informs me that he has seen 

 shells of aquatic snails similarly covered. His observations 

 were made at Cedar Point, which is also on Lake Erie, but about 

 twenty miles from Put-in-Bay, near Sandusky, Ohio. 



Spongilla fragilis is of course a sessile animal without any 

 very rapid means of distribution. On the other hand, a com- 

 paratively active animal, such as a rhyacophilid larva, in the 

 course of its wanderings, would be likely to carry a sponge some 

 distance from its point of origin and thus aid the more rapid 

 spread of the species. 



That a sufficient number of the caddis cases are invested 

 with Spongilla to make the larvae a factor in distribution is 

 to be seen from the percentage of covered cases observed among 

 those collected. • In one mass of material dredged over a distance 

 of twenty-five to thirty feet, there were twelve caddis-worm 

 cases and eight of them were encrusted with sponges. In another 

 haul there were three cases and one was covered. These results, 

 compared with other more casual observations, indicate that 

 from a third to a half of the cases bear the sponges. 



Ohio State University, Columbus, Ohio. 



