SCIENCE-GOSSIP. 



125 



THE GOAT-MOTH 



By Edward Ransom. 



A Sis well known the larva of Cossus lignipenla is 

 "^ an internal feeder, and its habits are, therefore, 

 difficult of observation. The eggs are laid in the 

 crevices of the bark of poplar, willow, ash, and other 

 trees about the middle of June. As soon as the 

 larvas are hatched they commence eating their way 

 into the interior of the tree, driving their tunnels 

 upwards, right up into the larger branches. As 

 they remain for three years in the larval state, the 

 damage they cause to the timber can well be 

 imagined, especially if they are present in any 

 numbers. I donot think, however, that they impair 

 the vitality of the trees in which they feed. I have 

 two poplar trees in my garden which for years 

 have been infested with these larvas, and also with 

 the larvae of Aromia moschota and sometimes, too, I 

 believe, with the larvae of Trochilium apiformis. 

 Nevertheless, these trees are most luxuriant in 

 growth. I have a piece of one of the larger 

 branches, which I cut from one of these trees, 

 showing the burrows of one of these larvae, and 

 there is not the least appearance of decay. When 

 a tree is pre-disposed to decay, or if the wet can 

 find entrance to their tunnels, then undoubtedly 

 they help to hasten the end. Probably they 

 also weaken the tree so that its branches are 

 more liable to be blown down in a heavy gale. 

 Even when a tree is very far advanced in decay 

 these larvae may still be found feeding on the half- 

 rotten wood. There is an old ash tree not far from 

 here the trunk of which is entirely hollow, leaving 

 only part of the outer portion standing, in which 

 these larvas may still be found in all stages of growth. 

 This tree is somewhat of a curiosity, as some of the 

 upper branches, being evidently unable to obtain 

 sufficient nourishment in consequence of decay of 

 the parent stem, have themselves thrown down 

 roots into the debris collected below in the hollow 

 trunk. These roots are hanging down inside the 

 trunk. 



The presence of the larvae of goat-moths in a 

 tree may often be detected by the peculiar odour 

 emanating from their tunnels, and also by the 

 appearance of a sort of sawdust (if I may so call it) 

 collected below, on the ground, around the trunk. 

 This wood-dust may be found also on the upper 

 sides of the branches, where it falls as it is pushed 

 out of the tunnels by the larvas as they carry on 

 their depredations. The larvas are full fed in the 

 autumn, and they then either spin a cocoon com- 

 posed of small pieces of wood gnawed from the 

 tree not far from the outlet of one of their tunnels, 

 or, quitting the tree, burrow below the ground. I 

 believe that they pupate below the ground far more 



often than is generally supposed. My own ex- 

 perience shows that their usual habit is to do so. 

 The reason that the pupae are so seldom found by 

 entomologists when pupa digging, is in consequence 

 of their wandering a considerable distance from the 

 tree in which they have been feeding before bur- 

 rowing. I have never found them at a less distance 

 than about ten feet from the trunk, and I have 

 occasionally seen the larvae wandering fully one 

 hundred feet from the nearest tree, evidently in 

 search of some suitable spot in which to burrow. 

 I could not ascertain any reason why they should 

 be so far away, as the ground was sufficiently soft 

 for them to burrow to a considerable depth quite 

 close to the trees. I have never known them 

 burrow so near to the tree that the branches could 

 in wet weather afford them any shelter. Possibly 

 they require more moisture than some species ; if 

 so, it is a probable explanation of this habit. What- 

 ever be the reason, most of us have, at one time 

 or other, noticed these larvae marching along a 

 country lane, or garden path, quite a distance from 

 any tree where they could have fed. 



When Cossus burrow below the ground they 

 spin a very tough cocoon composed of earth and 

 small stones. I have one in my collection meas- 

 uring two inches in length, being only a trifle longer 

 than the pupa. Although they leave the tree 

 in the autumn and immediately burrow, they do 

 not always spin the cocoon at once. I have 

 known them pass the winter in the larval state and 

 not commence to spin a cocoon until the middle or 

 end of March, or perhaps later. As the imagines 

 emerged in the following June, for so large a moth 

 they remained in the pupal state a very short time. 

 At other times the larvas are known to spin their 

 cocoons in the autumn. 



When searching for the pupae I find the following 

 plan very successful. In the early autumn I dig 

 over the ground round some tree in which I know 

 the larvae have been feeding. I commence digging 

 about four feet from the trunk and continue digging 

 as far away as practicable. If I am unsuccessful I 

 go over the same ground again after about a fort- 

 night's interval, and continue to do so at regular 

 intervals until the commencement of winter. By 

 this means I often find the larvas before they 

 commence to spin their cocoons. The cocoon so 

 much resembles a small clod of earth that it is 

 easily overlooked, and it is quite impossible to 

 search so large a portion of the ground as 

 thoroughly as when digging for pupa: in the usual 

 manner. 



Sudbury, Suffolk : March, 181)5. 



