26 BULLETIN 143, UNITED STATES NATIONAL MUSEUM 



ment of either male or female Mutillid was 14° C; the male stood 

 on his legs at 15° C. and the female at 17° C; the first crawling of 

 the male took place at 17° C. and the female at 18° C; all of the 

 males were active at 18° C. and all the females at 20° C; normal 

 activity of the males began at 22° C. and of the females at 24° C; 

 first paralysis due to temperature occurred in both males and females 

 at 46° C. ; the first male down occurred at 51° C. and the first female 

 at 62° C.'; all males were down at 53° C. and all females at 55° C. 

 It will be noticed that the zone of activity here embraces 35° C, 

 while it was found that for some of the sand-dune insects this zone 

 was narrowed to 14° C. 



The successful sand dune insects are capable of either enduring great 

 extremes or of avoiding them by choosing the times and places for their 

 activities The Mutillids which parasitize the larvae of bembecids are limited 

 in their choice of space by the lack of wings in the females. Being unable to 

 leave the surface of the sand except by entering burrows or climbing the sparse 

 vegetation, their success on the dune seems to be due to the high temperature 

 which they can endure. Thus their limitation in space seems to be compensated 

 by their increased endurance of high temperature. 



The specimens observed were for the most part Dasymutma 

 Uoculata (Cresson). 



SODND-rEODUClNQ ORGANS 



Both the male and female sexes of Mutillids are able to produce 

 sounds In the larger species the sound is loud enough to attract 

 one's attention at once while that made by the smaller species is only 

 noticed if the insect is held close to the ear. The sound is produced 

 by the rubbing of a transversely striated area on the base of the third 

 abdominal tergite against a sharp ridge on the under side of the 

 second ter-ite at the median apical margin. This is performed by 

 the insect by moving the third abdominal segment m and out ot the 

 second segment. Mercet (1902) states that these sound-producmg 

 structures are present only in the true Mutillids and that the genera 

 Apterogyna and Myrmosa and the species Myrmilla calva and 

 il/. c^imi do not possess sound-producing organs. 



Christ (1791) was the first one to mention the fact that Mutillids 

 were able to produce sound and has an interesting theory regarding 

 its purpose. His remarks, translated, are as follows : 



I found further that the female made a loud piping sound like the voice of 

 a young mouse if one held her between the fingers. When I heard this for the 

 first time and had a female Mutillid without wings between my fingers, 1 

 thought the sound came from a drone bee, a second insect; but I discovered at 

 once that this bee (Mutillid) made the sound itself by the friction of he first 

 segment of the abdomen with the following one lying under it, just like some 

 species of beetles make the same sort of noise if they rub the neck on the 

 prothorax. or the prothorax on the scutellum of the elytra. The first thing 



