Il8 THESENSESOFANIMALS 



The same behaviour can be demonstrated with the larger, 

 multicellular Hydra; the touch should be directed to the 

 tentacles which will come together and turn inwards to- 

 wards the "mouth", retracting slightly as they do so. This 

 is what happens in nature when a water-flea comes within 

 range of the hydra's tentacles and minute poisoned darts. 

 The tentacles seize the prey and convey it to the mouth. 



Spiders are singularly responsive to touch both on their 

 bodies or by means of a light touch on their webs — even 

 the vibrations caused by holding a struck tuning-fork near 

 the anchor strands of the webs will produce a reaction on the 

 part of the spider. 



Among the insects, a very fine demonstration of the extent 

 to which touch is used may be seen by the behaviour of 

 those species of ichneumon flies which have long antennae 

 and long ovipositors. The females, having mated, seek out 

 a tree trunk in which the larvae of other insects dwell at 

 the ends of the tunnels they have bored out in the wood. 

 The object of these particular ichneumons is to locate a 

 living larva and then insert their long ovipositors in order to 

 lay an egg from which their own larva will, in due course, 

 emerge to feed on the body juices of the larva so parasitized. 



I well remember watching this whole process on one occa- 

 sion in company with the late L. C. Bushby, one-time curator 

 of insects at the London Zoo. We were on a "bug-hunting" 

 expedition at Frensham Pond in Surrey when we saw a 

 female ichneumon on a rotten wood post. It was clearly 

 searching for an occupied tunnel among the dozens to be 

 seen in the post. 



First of all the ichneumon used its antennae with great 

 care, touching every now and then the outer edges of the 

 entrances of the tunnels. After some minutes, the ichneumon 

 paused, paid extra attention to one particular hole and then, 

 moving forward a trifle, it arched its body and bent its 

 abdomen forward so as to bring its ovipositor into place; 

 after which this long egg-laying tube was thrust into the 

 tunnel and an egg laid. It was a wonderful sight and the 

 whole operation took about seven minutes — it was a fine 

 example of the employment of the sense of touch in which 

 the antennae and the ovipositor each played its tactile part. 



