1234 MR. C. S. ELTON ON THE 



Railway Ditch. [Mites will often attack each other.. Fiona 

 longipalpis was seen to attack Limnesia fulgida and Hydrarachna 

 fuscata, and Mr. Soar states that L. fulgida will often attack 

 Eylais.'] 



Hydrarachna fuscata., which is not scarlet, has the peculiar 

 habit of crumpling up its legs and feigning dead when touched. 

 Mr. Soa.r states that he does not know of any other Water-niite 

 which does this, although mites sometimes are found resting in 

 a crumpled up position. Before we can say what the precise 

 use of this habit is, more experiments are required. But 

 the following occurrence shows that it may be an advantage 

 sometimes. 



Ex2)t. 7. A Hydrarachna schneideri and a FI. fuscata from 

 Railway Ditch were put in ix jar with a specimen of Agahus hipus- 

 tulatusirom a pond in Oxford Botanic Gardens in which no mites 

 had ever been seen, although regular collections had been made 

 for nine months. The beetle attacked and ate H. schneideri. 

 Meanwhile II. fuscata feigned dead during the disturbance and 

 remained unharmed. 



This experiment does not prove anything with regard to the 

 distasteful properties of H. schneideri, since the beetle was almost 

 certainly unused to scarlet mites. 



Uxpt. 8. In the autumn of 1921, a young 3-spined Stickleback 

 from a flood-pond near Railway Ditch was starved for three 

 days and then given a Tubifex, which it gobbled up. A Limnesia 

 fiilgida from Railway Ditch was put in with it. The fish dashed 

 at the mite and caught hold of one leg, but immediately let go 

 and left it. After this the fish Avent up to within a quarter of an 

 inch of the mite several times, but did not touch it. The mite 

 was left in with the fish for seven days, but still remained 

 uneaten, although the latter had now been starved for ten 

 days. 



Expt. 9. In the end of February 1922 a young 3-spined 

 Stickleback was taken in Railway Ditch and was starved for 

 four days. (ISTo mites were to be found in the ditch at this 

 time.) A Siraocephalus vetulus was put in and eaten eageily. 

 A nymph of Hydrarachna jjoludosa Thon. fi'om a halt stream at 

 Marcham was now put in. This species is coloured very brilliant 

 scarlet. The fish went up to it and took the mite into its mouth, 

 but immediatel}^ spat it out. It went up to the mite repeatedly 

 after this without eating it, and followed it round for some 

 time, clearly torn between its ravenous hunger and the un- 

 pleasantness of the mite. The latter was now removed. 



Two days later, the Stickleback (having now been starved for 

 six days) was given two Simocephahis, which it devouied. 

 H. jxdudosa was then introduced. This tinie the fish snapped 

 up and spat out the mite many times, but sometimes avoided it, 

 and never swalloAved it. 



This experiment shows among other things the efiect of 

 hunger on the reactions of the fish. 



