1926 ] Notes on the Behavior of Dineutes americanus 
159 
At the time of their appearance the beetles were extremely 
active and copulation took place quite frequently. Previous to 
mating the beetles swim along apparently without interest. The 
male then makes a dash for the female and, if successful, rides on 
her back holding on with his fore tarsi which are placed at the 
juncture of the elytra and thorax. They swim thus for several 
minutes, or more exactly the period varied as observed from one 
to twelve minutes. 
The population reached a peak in the first week in J une up 
to which time the beetles had spent their time near shore. During 
Fig. 1. Seasonal abundance of Dineutes americanus 
at Boston, Mass. 
the month the population decreased rapidly until at times it was 
rather hard to find specimens. The curve resumed an upward 
trend about the first of August and within ten days, thousands 
were present. No copulation among these was noticed and the 
insects preferred to lie quietly in the sunshine, or swim slowly 
about on the deeper water. They are not easily alarmed and not 
so readily disturbed by noise or movement as in the spring. The 
following figure, based on careful estimates represents the fluc- 
tuations of populations as observed for five years. 
