THE CANADIAN ENTOMOLOGIST. 39 



ON SOME AQUATIC LARV^, WITH NOTICE OF 

 THEIR PARASITES. 



BY H. F. WICKHAM, IOWA CITY, IOWA. 



During the past summer, while on a visit to the northern portion of 

 this State, my attention was attracted to the presence of numerous mud 

 cells on the lower surface of stones lying along the bands of the 

 Wapsipinicon River. These cells, most of them empty, with one end 

 forced off, somewhat resembled the single one with which some of our 

 common mud-wasps start their establishment on the ceilings of little-used 

 rooms, or on the rafters of outhouses, but very much smaller. The 

 largest measure about 1 2 mm. in length and 8 mm. in breadth, while the 

 small ones are only 5 mm. long and 2.5 mm. wide. 



After considerable search I finally succeeded in obtaining a curious 

 pupa from one of the large cells, quite different from any with which I 

 was previously acquainted. A cursory examination showed it to possess 

 four eyes, two on each side of the head, the components of each pair 

 being connected by a fine black line. This character directed suspicion 

 to the probability of its being a Gyrinid. and confirmation was furnished 

 by finding the legs, though rather poorly defined, evidently belonging to 

 a beetle of that family. It was finally decided to be Dineutes assimilis, 

 Aube, the common large whirligig of our country. A half day of stone- 

 turning resulted in the finding of more pupi"e and several larvae, as well as 

 two or three of the soft and helpless freshly-emerged beetles. A number 

 of the inhabitants of the little cells were also found in all three stages, and 

 proved to be a Gyrinus, probably //V//^.y, Aube.* 



Two of the Dineutes pupae were each seen to be accompanied in their 

 cells by a little white larva of rather robust form, evidently there with 

 intent to do great bodily injury. Bringing them home in their original cells, 

 I was able to watch the growth of these little creatures until one trans- 

 formed to a pupa, and finally disclosed a beetle, which proved to be a 

 species of Brachinus, probably janthinipennis, Dej. However, the 

 determination cannot be considered authoritative, because the beetle died 

 before attaining its full colours. The larva lies in the cell of its host and 

 extracts the juices through an opening made in one of the wing-pads ; the 

 maggot-like body is adorned, but not supported, by six very soft and 

 short legs, which can be of little service except perhaps as " feelers " in 



* Detailed descriptions of these larvae, with figures, may be found in \"ol. II., No. 

 4, of the BuUetin from the Nat. Hist. Lab. of the State Univ. of Iowa. 



