U. S. D. A., B. E. Bui. 66, Part II. Issued April 23. 1907. 
SOME INSECTS INJURIOUS TO TRUCK CROPS. 
THE WATER-CRESS SOWBUG. 
(MancaseUus brachyurus Harder.) 
By F. H. ChIttendbn, 
Entomologist in Charge of Breeding Experiments. 
During the past three years this isopod has attracted very consid- 
erable attention because of its occurrence in troublesome number- in 
water cress (Nasturtium officinale) grown for market in portions of 
Virginia, West Virginia, and Pennsylvania. The species is purely 
aquatic, thus differing from our common dooryard sowbugs, which, 
although most abundant in moist locations, are strictly terrestrial. It 
belongs to an entirely different family, the Asellida?. which contains 
three genera, mostly fresh- water forms, inhabitants of streams, wells, 
pools, and lakes. 
DESCRIPTIVE. 
This species is so distinct from the more common sowbugs (Onis- 
cidse) that a brief description will suffice. Its general appearance 
is shown, dorsal view, in figure 3. The body is much depressed, and 
the legs are long and strong. Seen from the side, it is decidedly 
shrimplike. The peculiar structure of the antennae may be noticed 
in the illustration. They terminate in long flagella. composed of 
many joints. When mature this sowbug attains a length of 13 or 14 
millimeters, or a little upward of half an inch, and is a little more 
than twice as long as wide, and gray in color. This creature is not an 
insect, but a crustacean, and therefore classed with crayfish and crab-. 
A detailed description is given by Miss Richardson, who briefly men- 
tions McKees Spring, Gaylord, and Lexington, Va.. as localities 
where this sowbug was " reported injurious to water cress." 
By recent correspondence we have obtained necessary information 
in regard to the habits and manner of operation of this sowbug. and 
we have also been successful in ascertaining what promises to be a 
very perfect reined}' for the pest in its occurrence in streams ami in 
spring water. It appears to a licet cress only below the surface of the 
water, attacking the roots and lower leaves, and cutting off the stems 
a Monograph of the [sopods of North America. By Harriet Richardson. Bui. 
54. U. S. National Museum, Washington, L905, pp. 411-412, Bgs. 460-461. 
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