yan. 2 2, 1874J 



NATURE 



219 



traveller to support the theory originated by Mr. Bates of 

 the purpose and cause of what is termed " mimicry " in 

 the animal world, since it was he who first directly ob- 

 served insectivorous birds reject the Heliconii and allies 

 as food. In Nicaragua he found that a tame monkey, 

 which was extremely fond of insects, and would greedily 

 munch up any beetle or butterfly given to him, would 

 never eat the Heliconii. He would sometimes smell them, 

 but invariably rolled them up in his hand and dropped 

 them quietly after a few moments. One large spider used 

 to drop them out of its web when put into it, but 

 another spider seemed to like them, showing that the 

 smell and taste is not universally, although very 

 generally, displeasing to their enemies. The Lam- 

 pyridEE, among beetles, which are almost as frequently 

 mimicked as the Heliconidai, were rejected by monkeys 

 and fowls, as they are known to be rejected by insecti- 

 vorous birds. Among the new cases of mimicry obser\'ed 

 by our author was a longicorn beetle, which most decep- 

 tively resembled a hairy caterpillar — a kind which it is 

 well known are never eaten by insectivorous birds. More 

 remarkable is the account of the behaviour of a green 

 leaf-like locust among insect-eating ants. " This insect 

 stood immovably amongst a host of ants, many of which 

 ran over its legs without ever discovering that there was 

 food within their reach. So fixed was its instinctive know- 

 ledge that its safety depended on its immovability, 

 that it allowed me to pick it up and replace it 

 among the ants, without making a single effort to 

 escape. This species closely resembles a green leaf, and 

 the other senses, which in the Ecitons appear to be 

 more acute than that of sight, must have been completely 

 deceived. It might easily have escaped from the ants 

 by using its wings, but it would only have fallen into as 

 great a danger, for the numerous birds that accompany 

 the army of ants are always on the look-out for any insect 

 that may fly up, and the heavy locusts, grasshopers, and 

 cockroaches have no chance of escape." 



The view that conspicuously coloured creatures, and 

 those that seem to court observation, have some special 

 protection, and that the gay colouring is a warning signal 

 to their enemies not to touch them, was first apphed by 

 myself to explain the brilliant colours of many cater- 

 pillars. It is now, however, found to have a very wide 

 application, and Mr. Belt is so convinced of its truth that 

 he is able successfully to predict the behaviour of other 

 animals towards an unusually conspicuous species. Most 

 frogs are of more or less protective tints — green or brown 

 according as they live among foliage or on the ground. 

 They feed only at night, and they are all preyed upon by 

 snakes and birds. One species, however, found by Mr. 

 Belt, was of a bright red and blue colour, and hopped 

 about in the day-time without any attempt at conceal- 

 ment. He was at once convinced, theoretically, that this 

 frog must be uneatable. He accordingly took it home, 

 but neither fowls nor ducks would touch it. At length 

 one young duck was induced to pick it up, but instead of 

 swallowing it, instantly threw it out of its mouth, and 

 went about jerking its head as if trying to throw off some 

 unpleasant taste. The skunk, whose offensive secretion 

 is universally dreaded, is a similar instance among 

 mammalia. Its white tail laid back on its black body 

 makes it very conspicuous in the dusk, when it roams 



about, so that carnivora may not mistake it for other 

 night-roaming animals. When we consider that such 

 cases as these are probably very numerous ; that instances 

 of clearly protective colouring'are still more so ; that both 

 these kinds of colouring may vary almost infinitely, and 

 that there is certainly some unknown influence which 

 tends to produce certain colours in certain localities ; and 

 when we further consider that all these causes have been 

 in a continual state of change with changing conditions 

 of existence, organic and inorganic, and have acted and 

 combined with each other in [countless ways for untold 

 generations, we have some ground for concluding that 

 colour in nature may have been produced with less as- 

 sistance from sexual selection than Mr. Darwin thinks is 

 due to that undoubtedly powerful agent. 



A very fuU and interesting account is given of the leaf- 

 cutting ants (CEcodoma sp.), and though these have been 

 so often described, our author has much that is new to 

 teU about them. In his mining operations he cut through 

 some of their subterranean galleries, and from his exami- 

 nation of these he arrives at the conclusion that the ants 

 do not feed on the leaves which they gather in such enor- 

 mous quantities, but that they use them to form beds for the 

 growth of a minute fungus on which they and their young 

 live. These ants are so destructive to certain plants by 

 entirely destroying their foliage, that many species cannot 

 be cultivated without constant care and protection. It 

 becomes an interesting point, therefore, to determine by 

 what means many of the less vigorous or less abundant 

 species are preserved. It has long been known that there 

 is a very close connection between certain trees and ants. 

 Many Melastomas have a kind of pouch at the base of 

 each leaf, which serves as a habitation for small ants. 

 These have been described by Mr. Spruce, as well as 

 others on the leaves of species of Chrysobalane;i3 and 

 Rubiaceffi, &c., in a paper read before the Linnasan 

 Society but not yet published ; and he arrived at the 

 conclusion that these structures had become hereditary 

 through the adaptation of the plant to the constant para- 

 sitism of the insect, although he did not consider that the 

 ants were of any actual service to the plant. Mr. Belt 

 figures the leaf of a Melastoma possessing these pouches 

 as well as a curious thorny Acacia, the thorns of which 

 are very large and hollow, and are tenanted by ants. In 

 this case the constant attendance of the ants is secured 

 by a provision of food in the shape of little stalked fruit- 

 like glands on the leaves, which the ant feeds on. The 

 hollow stems of the Cecropias are also infested by ants, 

 and they always abound on Passion-flowers, feeding on 

 the honey glands of the flower. Now Mr. Belt believes, 

 and apparently with good reason, that in all these cases 

 the ants are protectors of the plant against herbivorous 

 insects, such as caterpillars, cockroaches, earwigs, &c., 

 but especially against the leaf-cutting ants ; and that on 

 account of this service the plants have in many cases 

 become specially modified so as to supply food or shelter 

 to the ants which are so useful to them. It is a suggestive 

 fact that introduced trees and shrubs are more subject to 

 the attacks of the leaf-cutting ants than native species. 

 They do not possess either the disagreeable juices or the 

 insect protectors that the latter have in the course of 

 ages acquired. We have here an altogether new view of 

 the inter-relations of plants and insects, which may, in 



