56 A YEAR OF COSTA RICAN NATURAL HISTORY 



larva "sit up and take notice" when a squirming worm 

 suddenly appeared in his tumbler, to see how he followed 

 its movements until the chance came to strike out for it 

 with his jointed mask with its sharp jaws at the end, then 

 how he held the prey and chewed away until the last wrig- 

 gling bit had been eaten, when he immediately started after 

 a second worm. The large larvae sometimes ate nine or ten 

 blood-worms as fast as they could be dropped in and one 

 could see them "swelling wisibly" and trace the red worms 

 in the alimentary tract through the thin body walls. The 

 little dragonfly larvae were often turned head over heels 

 by the prey, but they hung on and continued to eat no matter 

 what position they were knocked into by the unfortunate 

 blood-worm. Even Thaumatoneura, which probably feeds 

 on quite different larvae in its native waterfalls, ate the 

 blood-worms in confinement if these were made to wriggle 

 over the stone directly in front of its head. I never saw 

 these sluggish larvae pursue the blood-worms as other species 

 did. Collecting the blood-worms was easy for all that was 

 necessary was to hold a water net at the narrow end of a cer- 

 tain ditch, and the worms carried by the current were caught 

 and held by the net. We gathered them for months and the 

 supply showed no signs of failing. On February 24 we 

 counted the worms that passed downstream, without any 

 disturbance on our part, the number reaching one hundred 

 and fifty in five minutes, and on March 11 we counted one' 

 hundred and eighty in the same space of time. The only 

 unpleasant feature of gathering them was the dirtiness of 

 the water in the ditch — a house drain — but it is the habit of 

 these worms (which are world-wide in their distribution) 

 to live in such water. 



One day in December we supposed we had gathered plenty 

 of food, chiefly Agrionine larvae and copepods, to last for 

 six days, but on examining the dish some hours later, this 



