1 68 



SCIENCE- G OS SIP. 



NOTES OX SPINNING ANIMALS. 

 By H. Wallis Kew. 



i i oiiUiiiieil from page 131.) 



V.. Spinning Beetles. 



V MOXG the few insects capable of spinning in 

 -*--*- the imago state are the water-beetles of the 

 family Hydrophilidae — well known in the person 

 of Hydropldlus piceus, the great harmless water- 

 beetle of the aquarium. 



Here the females spin cocoons or silken bags, 

 sometimes of complex structure, in which their 

 eggs and newly -hatched larvae are enclosed and 

 protected. 



The egg-cocoon of Hydrophilus piceus is nearly 

 an inch broad, somewhat roundish, slightly nar- 

 rowed and truncated anteriorly, where it is fur- 

 nished above with a spike or "mast." recalling the 

 horn on the anal segment of a hawk-moth cater- 

 pillar. The structure is spun from a paired spin- 

 neret at the hinder extremity of the beetle. When 

 complete it floats at the surface of the water, 

 usually attached to a leaf or some small floating 

 object, and always with the spike above the sur- 

 face. The young larvae, which remain in the 

 cocoon for a while after hatching, finally escape 

 near the base of the spike, where the cocoon is only 

 slightly closed. This floating nest, and the manner 

 in which it is spun, were described by the cele- 

 brated Lyonnet ; and later, in 1S09. Miger, who 

 also had witnessed the spinning of the cocoon, 

 published his often quoted memoir and illustra- 

 tions ('). 



The beetle observed by Lyonnet was kept in a 

 trough, where it was supplied with filamentous 

 algae, floated on the water by means of wooden 

 shavings. Before long Lyonnet saw the beetle 

 setting about the formation of a cocoon. She ex- 

 tended the hinder rings of the body and opened 

 the last of all, exposing a cavity in which was seen 

 a whitish disc, giving off two small prominences 

 side by side, each enclosing a delicate tube about 

 a line in length, stiff towards the base, but flexible 

 and elastic towards the tip. These two tubes 

 formed the spinneret. They always moved to- 

 gether, but each contributed a separate thread. 

 Lying back downwards near the surface of the 

 water, beneath or amongst the algae, the beetle 

 began to weave one side of the cocoon ; and as the 

 work proceeded she was careful to press and flatten 

 the growing structure, moulding it with her fore- 

 feet against her body, and thus giving it the form 

 of a flattened arch. After the first section, which 

 formed the upper side of the cocoon, was finished, 

 the insect turned over and wove another piece, 



(1) Lyonnet and Jliger have recently been quoted at length 

 by Miall.op. cit., pp. 61-86 ; and it is Xrom this source that the 

 present notes of the work of these authors are derived. 



exactly the reverse of the first, to form the under- 

 side. The two curved pieces were now woven 

 together, and thus the body of the cocoon was 

 constructed. The work so far had occupied about 

 an hour and a quarter. For about two hours the 

 beetle remained still with her body buried in the 

 cocoon, from which, however, it became evident 

 that she was gradually withdrawing. She was in 

 fact laying her eggs. She now withdrew her body 

 completely, and began to spin about the open 

 mouth of the cocoon, gradually narrowing and 

 closing it. Afterwards she proceeded to spin the 

 spike, which gradually rose above the water. The 

 work was complete in five hours, after which the 

 cocoon was left floating. 



Miger relates that he kept several specimens of 

 this beetle in a vessel of water with aquatic plants, 

 and that at length he saw a female spin a cocoon. 

 She attached herself to the under-side of a floating- 

 leaf, clasping it with her forelegs and applying 

 her abdomen to its under surface. The two tubes 

 of the spinneret could be seen to be pushed in and 

 out with rapidity, while a gummy liquid was 

 passed from them and drawn out into threads ; 

 and these, being attached to the leaf, gradually 

 surrounded the tip of the abdomen, forming at 

 length a semicircular pouch in which that part of 

 the beetle was enclosed. After about ten minutes 

 the beetle turned sharply round, letting go the 

 leaf and bringing her head downwards, but with- 

 out withdrawing the abdomen from the cocoon. 

 The leaf was now held by the hindlegs only, one 

 being placed on each side of the cocoon. The 

 insect continued to work steadily for nearly an 

 hour and a half : and. through the transparent wall 

 of the cocoon, Miger could see the movements of 

 the spinneret, until at last the gradual addition of 

 threads made the structure opaque. The beetle 

 then laid her eggs, and afterwards closed the 

 cocoon slightly, and began to form the spike. 

 The tips of the wing-cases, which were a little 

 opened, were brought to the surface of the water. 

 and the spinneret was seen to be in continuous 

 and rapid motion. The spinning of the spike 

 took more than half an hour, at the end of which 

 time the completed spike — which, as Miger sup- 

 posed, served to supply the cocoon with air — rose 

 considerably above the water. The whole work 

 occupied about three hours. 



J. Fullagar, among more recent observers, men- 

 tions having seen the Hydrophilus piceus spin her 

 cocoon in an aquarium. He gives a sketch show- 

 ing the beetle holding the unfinished cocoon 

 between the hindleers, and another showing the 



