176 Mr Sharp, Modification and attitude of Idolum diabolicum, 



cannot be its natural plant as the only ones on the island are in 

 our garden. I doubt if it has any special plant, but its coloured 

 legs hanging from any tree form an attraction to flies. In order 

 to test this I placed pieces of coloured paper on trees and noticed 

 that flies would often fly down and at times beetles. The position 

 given in the sketch was its favourite one whilst in captivity. The 

 colours are fairly correct. In the dried specimen the greens have 

 gone yellow and the fore-legs faded." In a subsequent letter 

 Mr Muir emphasises the fact that /. diabolicum captures its 

 prey, as this flies down, by closing the tibia on the femur, and 

 not by darting out the leg as other Mantises do. 



Although the appearance of Idolum diabolicum, as shown in 

 the sketch (Plate II.) is very striking, yet examination shows that 

 the modification from other Mantids is but slight; and a com- 

 parison with what we know as to other Mantidae suggests that 

 the question of most interest is the relation of the modification to 

 the habits of the creatures. 



The points of modification are (1) the great size of the front 

 legs, (2) the colour of the coxae. 



(1) The front legs are remarkably large but the part of them 

 that is most enlarged is the coxa. The increase of this part is 

 effected not by an enlargement of the whole of the limb, but by 

 the development on each side of it of a plate-like dilation. The 

 slender coxa usual in Mantidae generally, and in the tribe 

 Empusides to which Idolum belongs, is perfectly well-defined, but 

 there is a large flap added on each side. These flaps appear to be 

 similar in their nature to the large flaps on the thorax as well as 

 to those at the tips of the middle and hind femora, and at the sides 

 of the abdomen, and it is to be remarked that in this Insect there 

 are also flaps on the middle and hind coxae. The possession of 

 these appendages is a special character of Idolum and its immediate 

 ally Gongylus ; they are more largely developed in Idolum than in 

 Gongylus, being almost absent on the hind legs of the latter genus. 

 In addition to this the front femur of Idolum has also a flap-like 

 dilatation along its inner or upper margin while the spines on the 

 upper side of the femur are of unusual length. The great shield 

 or hood of the thorax is found in various other Mantidae ; it is 

 seen in the family in a great variety of sizes and shapes, but it is 

 at its maximum of development in Idolum. In the two allies of 

 Idolum — Empusa and Gongylus — it is but little developed, there 

 being scarcely any trace of it in Empusa, while in Gongylus it is 

 small. Both of these Insects are floral simulators, and both of 

 them use the prothorax as part of the simulation, but in Idolum, 

 notwithstanding the great size of this part, it appears to be of not 

 much importance in this respect. Idolum may therefore be de- 

 scribed as an Empusid, with the epidermal flaps of the coxae and 



