174 COLEOPTERA— BEETLES 



cut worms, caterpillars, etc. The searcher Calosoma scruta- 

 tor, a brilliant green species with metallic border on elytra 

 and margin of prothorax which, while a general feeder on 

 ground-living insects, is also credited with climbing trees 

 to feed upon canker worms. The Calosoma sycoyhanta, an 

 old-world species that is especially useful in keeping the 

 Gipsy moth in check, has been introduced into Massachusetts 

 in hopes that it may assist in control of this pest. 



There are several families of aquatic Coleoptera which live 

 almost entirely in water, although at times the adults issue 

 and fly. The carnivorous water beetles ( Dysticidce) have 

 peculiar circular or oval sucking disks on the front legs, and 

 are distinctly aquatic, the adults appearing out of water, 

 and like the ground beetles, they feed quite exclusively upon 

 other animal life and doubtless occupy a somewhat impor- 

 tant place in the relations of aquatic forms. 



The HydroiMlidcB are more distinctly herbivorous and 

 may be considered as water scavengers, feeding upon vege- 

 table debris and serving as important members of the 

 aquatic association. It is a large family, including a great 

 many genera and species, but from their habits are naturally 

 of little economic importance. 



The Gyrinida^ or whirligig beetles are quite remarkable 

 for their movement on the surface of water. They dart 

 around with the greatest rapidity, making all sorts of irregu- 

 lar movements but when a group of them are together they 

 form a bewildering array of darting forms. Although 

 dozens or even hundreds of them may be in a group they 

 seldom if ever seem to have a collision among the different 

 individuals in the cluster. A remarkable feature in their 

 structure is the separation of the compound eye at the side 

 of the head so that the upper portion is above \Vater and 

 the lower portion submerged. They are said to feed mainly 

 upon flies and stranded insects of various kinds that are 

 caught on the surface of the water. One of our common 

 species is tlie Dinniies americana. 



Family Platypsyllidse. — The Plafypsyllida' is a small 

 family including a very remarkable parasite of the beaver. 



