Earthworms use their soft sucking mouths to seize 

 plant debris on the surface of the ground while they 

 are extended from burrow openings at night. Al- 

 though these worms have no eyes, their skins are 

 sensitive to light (except red light), and each indi- 

 vidual will draw back into its tunnel if illuminated. 

 Anglers often hunt them with a ruby lens on a flash- 

 lamp, taking advantage of the animal's blindness to 

 this part of the spectrum useful to man. 



All over the world, earthworms have many natural 

 enemies. The national bird of Australia, the kooka- 

 burra or "laughing jackass," is actually a kingfisher 

 whose remote ancestors gave up diving for fish and 

 took to earthworms instead. Elsewhere moles tunnel 

 after earthworms. Skunks dig them out or pounce on 



The European medicinal leech Hirtido medicinalis 

 has its larger sucker at the rear end ( below ) . This 

 leech is still being imported for sale in the United 

 States, although it thrives in many ponds in Amer- 

 ica as an introduced animal. ( P. S. Tice ) 



them at the surface. Owls eat amazing numbers and 

 feed them to their young. Robins and other birds use 

 earthworms as an important part of their diet. 



Recent experience in Ann Arbor, Michigan, has 

 emphasized the extent to which earthworms bury 

 leaves and robins eat earthworms. In that city, prized 

 elm trees were sprayed heavily with insecticide to 

 check the spread of bark beetles carrying the Dutch 

 elm disease. Poison-coated leaves fell to the ground 

 in autumn, and were pulled by earthv\orms into their 

 burrows for winter meals. The worms digested the 

 plant matter without noticeable harm from the in- 

 secticide. But when the robins arrived the following 

 spring, at the end of northward migration, the fliers 

 encountered poison-charged earthworms. The robins 

 ate so many worms that they succumbed to the in- 

 secticide. Soon Ann Arbor's formerly abundant rob- 

 ins were no more. 



The Leeches 



( Class Hinulinea ) 



Most leeches will take a blood meal from a verte- 

 brate animal if they have an opportunity. Only a 

 few, however, require this food, having become truly 

 parasitic. The rest get along quite well on a mixed 

 diet of snails, insect larvae, crustaceans, and small 

 bristle-footed worms, swallowing these victims whole 

 into the capacious crop portion of the digestive tract. 



Leeches swim gracefully by undulating the body. 

 Those that are flattened make especially rapid prog- 

 ress. At the end of the journey, however, all leeches 

 settle down and hold to something solid by use of a 

 muscular suction disk just ventral to the anus at the 

 posterior end of the body. Most leeches have a sec- 

 ond suction disk surrounding the mouth, and often 

 stitch themselves along from place to place like an 

 inch worm, holding to the bottom with one sucker 

 and then the other alternately. 



The saliva of blood-sucking leeches contains a 

 powerful anticoagulant (hirudin), which prevents 

 formation of a clot. It may also serve to preserve a 

 blood meal, since, if permitted, a leech will usually 

 swallow enough to last for several months. Almost as 

 rapidly as the blood is taken in, the leech's excretory 

 organs (nephridia) dispose of the water, concentrat- 

 ing the meal for maximum nourishment. A half- 

 ounce leech has been known to gorge itself with two 

 and one-half ounces of concentrated blood and then 

 survive with no more to eat for fifteen months. 



The leeches include a number of exceptional ani- 

 mals radically unlike other members of their class. 

 One {Acanthobclella) has bristles and retains a true 

 body cavity in adult life; otherwise leeches lack bris- 

 tles, and the body cavity of the embryo is obliterated 

 by a meshwork of connective tissue, muscles, and 

 expanded portions of the blood system. 



[ continued on page 225 1 



