Acrodact\la:\ BRITISH ICHNEUMONS. 133 



2. degener, Hal. 



Acrodactyla degener, Hal. Ann. Nat. Hist. 1839, p. 117, (f 9 . 



Palpi stramineous ; antennae basal ly stramineous ; metathorax canalic- 

 ulate ; abdomen infuscate-piceous with the incisures more or less black ; 

 legs stramineous, the hind ones with their tarsi and apices of their tibiae 

 infuscate ; stigma piceo-stramineous. Length, 3^ — 4^ mm. 



The above description of Haliday is sufficient to distinguish this species 

 from the last, though it is well to further note that the mandibles are 

 testaceous, not stramineous ; the face is centrally less prominent ; the 

 two basal flagellar joints are of subequal length ; the basal segment is 

 longer with the spiracles inconspicuous ; the nervures of the hind wing 

 are all pellucid, its first recurrent straight and ner\'ellus wanting. It was 

 sufficiently distinguished originally, however, by the basally paler antennae, 

 canaliculate metanotum, constantly paler stigma and smaller size. 



" In the same situations with the last " (Haliday). Parfitt tells us he 

 once found the reddish larva of this species feeding on a small spider in 

 Devonshire (Trans. Devon. Assoc. 1881, pp. 41— 2): "The body of the 

 spider was not large enough to contain the lan-a, so that part of it was 

 exposed. The spider lived until the larva was ready to undergo its change 

 into pupa. It then spun a cocoon, fusiform and angular, attached at both 

 ends to the glass cover of the box after the manner of a hammock. It 

 remained in pupa about a fortnight, and came out September 19th, 1874." 

 Pickard-Cambridge refers to the exhibition at a meeting of the Zoo. Soc, 

 15th Februar}-, 1881, of examples of this parasite, bred by him the pre- 

 ceding year in Dorsetshire from larvae adhering to the outer surface of 

 the abdomen of two spiders, Linyphia obscura, Bl. and Z. zibn'na, Menge., 

 together with their victims and empty cocoons {cf. Spiders of Dorset, ii. 

 579). He states that "these larvae are in some seasons very abundant: 

 I have found them not only on the above-named spiders, but on several 

 species of Theridion, as well as on other species oi JJnyphia, and on some 

 Epeirae. It is possible that more than one species of parasite has been 

 concerned, though all the lar\-ae which have come under my own notice 

 appeared to be identical. ]Mr. Parfitt seems to have been under the im- 

 pression that the larva from which he bred A. degener was an internal 

 parasite, obliged to come outside owing to the body of the spider being 

 insufficient to contain it. This is, I think, a mistake. These external para- 

 sites are probably hatched from eggs affixed to the outer surface of the 

 spider's abdomen, or at any rate ver}- slightly inserted " ( Kntom. 1882, 

 p. 216). 



Bridgman records this species from Norwich and Brundall in Norfolk ; 

 and Bignell from Dousland in Devon, towards the end of August. The 

 latter gives (Trans. Devon. Assoc. 1898, pp. 471-2) a very full account of 

 its economy upon Linyphia obscura. He says that he believes he is the 

 only person who has ever witnessed the ichneumon's attack on a spider in 

 its native haunts. Having selected her victim, she apjiroaches it with 

 care, but it drops from its bough by its silken thread. The ichneumon 

 does not appear perturbed at this manoeuvre, but walks ver}- leisurely 

 down the thread itself to the spider, whom she coaxingly touches with 

 her antennae. The spider then drops further and, in a few seconds, the 

 fly follows and again touches the spider, who, " knowing her foe, resigns 

 herself to her fate and does not move. The fly turns round, walks back- 



