828 



THE NATIONAL GEOGRAPHIC MAGAZINE 



So 1936 ended with good progress made, 

 but a great deal still to be learned, and an- 

 other summer seemed a long way off. But 

 it came at last, with the hills burned bare a 

 full two weeks earlier. 



And yet the lirst few da\'s of hunting 

 brought only disappointment. Not a single 

 Ocnaea smithi did I find on the old hunting 

 grounds, even on Cyrtid Hill where I had 

 found so many the year before. 



I tried to resign myself to another year's 

 delay, and to settle down to the finishing of 

 my Psammy life-history prints. 



I was sitting at my typewriter that day 

 trying to concentrate upon writing captions 

 for photographs, but I was uneasy. Then I 

 became conscious of a strong urge, a desire 

 to try hunting in a new direction, to the 

 west. Of course I followed the impulse. 



I came to unfamiliar roads that wound 

 along new adobe hills, and, at the first place 

 1 stopped to hunt, ran slap-bang into a 

 regular epidemic of Ocnaea smithi parasites! 



That first afternoon I found twelve para- 

 sitized spiders with the larvae still in their 

 bodies, besides many emerged larvae, pupae, 

 and adults. I learned afterwards that these 

 conditions existed only in a limited area 

 about equal to four city blocks, but that, 

 within that district, from 25 per cent to 60 

 per cent of the trapdoor spiders had been 

 attacked by these insect racketeers. 



"CELLOPHANE SHEATH" MYSTERY SOLVED 



With a wealth of material at hand, the 

 final solution of The Case of the Cellophane 

 Sheath was soon reached. Even the life 

 of the larva within the abdomen of the 

 spider was easy to observe, for the white 

 maggots showed clearly through the dark 

 but transparent skin of the spiders. 



Judging by various known facts, it seems 

 quite certain that the female Ocnaea smithi 

 fly scatters her eggs over the ground while 

 flying. Obviously this action cannot be 

 photographed. Nor can we follow, with the 

 camera, the strange search of the micro- 

 scopic larva for its host. But an experi- 

 ment proved that these minute larvae go 

 hunting for the trapdoor spiders and are 

 not simply "hitchhikers" that wait to at- 

 tach themselves to a passing spider, as do 

 some other larvae of the Family Cyrtidae. 



In the laboratory, smithi larvae hatched 

 in a glass cage found their way into trapdoor 

 tubes, which T had sealed with strips of 

 paper so that I could tell whether the own- 

 ers had opened their doors. After several 



weeks, I broke my still-intact seals and 

 examined the spiders. Five out of twenty- 

 five were parasitized! Through infinitesi- 

 mal "chinks in the armor," many smithi 

 larvae had penetrated several of the trap- 

 doors and attacked the spiders (page 821). 



AN INSECT WARPLANE 



A bit of imagination will enable us to 

 visualize this epic quest of the tiny crea- 

 tures in Nature. The mother fly, a gro- 

 tesque insect airplane, cruises slowly over a 

 tangled jungle of dry grass and weeds. Her 

 powerful wings beat the air with an audible 

 hum, like the drone of a far-off sky pirate, 

 as she showers potential death, in the form 

 of hundreds of microscopic eggs, on the 

 trapdoor civilians below. 



ilany of the eggs will undoubtedly be 

 lost or destroyed ; others will stick to the 

 dry stalks and hatch there. But we will 

 follow in fancy the flight of one egg that 

 safely reaches the earth below. 



How dift'erent is the infancy of Psammy 's 

 baby as it awakens upon a soft cushion of 

 preserved food so marvelously provided by 

 a mother's "foresight"'! But the Cyrtid 

 fly's baby emerges from the egg to find her- 

 self a homeless waif, abandoned to shift for 

 herself on the cold, bare ground. (The same 

 would be true of a male. ) She is so tiny 

 that, to her, the dry jungle above must 

 seem like a great forest. 



But she does not seem to be dismayed. 

 She just stretches and starts out, following 

 her "hunches" as she toddles along through 

 a strange and lonely world where grains of 

 sand are huge bowlders and little pebbles 

 are thousand-foot mountains. 



On and on she goes, guided unerringly 

 by the still voice of Nature. Surely the 

 little traveler must get hungry, but she 

 never makes the mistake of stopping to at- 

 tack some tempting insect along the way. 

 She has just one destined host, and wall not 

 stop until she finds it. 



And so at last she reaches the massive 

 door of her host-to-be. She seems to recog- 

 nize it instantly — and down she goes. To 

 us it may look like a tiny, snug-fitting trap- 

 door, but to the little traveler the water- 

 proof joint is a wide passage, easily trav- 

 ersed. 



Down the silk-lined tube she hurries, and 

 climbs onto the huge and unsuspecting 

 spider. No need to hesitate. This is her 

 goal! She bores into the hairy skin. 



Home at last! 



