Distribution of Passalus unicornis, Serv. 159 
XX.—The Occurrence and Distribution of the Beetle, Passalus 
unicornis, Serv., in the Antilles and the Northern portion of 
South America. By Symington Grieve. 
(Read 23rd February. MS. received 26th February 1914.) 
In the spring of 1906, when I spent some time exploring the interior of 
the mountainous island of Dominica, I came across this species when 
searching for the much larger and well-known beetle Dynastes hercules, 
Linn. 
I had captured several specimens when moving about in the evenings, 
but had no idea of the numbers to be found until we began breaking up 
fallen and rotten trees in the forests. The nearer the timber approached 
to the state of touch-wood, the more numerous were the Passalus wnicornis, 
Sery., to be found, as the softer the wood, the insects were able with greater 
ease to tunnel deeper into the logs. I found the larve in different 
stages of development, and also the mature beetles, some of them being 
the hosts of large numbers of parasitic mites. From what I saw, I came to 
the conclusion that the mature beetles moved about during the night, and 
returned to their burrows in the wood of the fallen trees with the return 
of daylight. These beetles are probably to be found at all elevations in 
Dominica in small numbers, but possibly only breed at elevations of over 
1500 feet, as it was only at or over that height that I found the larve in 
the fallen and decayed trees. 
The ravages of the insects, as far as I discovered, were confined to the 
dead wood of the fallen trees; but the long and large tunnels they made 
were of such a nature that the whole of the main stems were perforated 
by their burrowing, which was in almost every instance longitudinal to 
the stem. 
It was to some extent by chance that I came across this beetle in its 
hidden tubes within the trees. When at a place at an elevation of about 
2000 feet among the mountains, I heard that at times specimens of Dynastes 
hercules, Linn., could be obtained, and, as its distribution in the Antilles 
is somewhat remarkable, I was anxious to procure specimens. 
Dynastes hercules, Linn., although abundant in the north of South 
America, is not found on any of the Antilles, except Dominica, and 
in the latter at times it becomes very rare, only once more to become 
abundant after the lapse of a period—probably from the occurrence of a 
number of fertile females during a certain year. 
I took with me in my search seven or eight of my black men, armed with 
