The phenomena, known as "protective resemblance," or similarity to inanimate objects or vegetation, and the kindred phenomenon of "mimicry," or beneficial likeness to certain protected species of animals, are common in the group. In these particulars, considered in their entirety, spiders show a marked contrast to other Arachnida, such as the scorpions, pedipalps, book-scorpions and so-called harvest spiders, which by comparison are remarkably uniform, within the limits of the orders, in structure, habits and other respects.
One interesting phenomenon in spider-life seems to be directly and certainly traceable to this influence, and that is mimicry of ants.
But since ants are not persecuted by these two families of Hymenoptera, the greatest enemies spiders have to contend with, it is evident that mimicry of ants is of supreme advantage to spiders.
The last and the worst of the Cid ballads are those which betray by their frigid conceits and feeble mimicry of the antique the false taste and essentially unheroic spirit of the age of Philip II.
The arboreal life of the tropical forests has developed the treeclimbing habit among snakes as well as among frogs and toads, and also the habit of mimicry, their colour being in harmony with the foliage or bark of the trees which form their " hunting-grounds."
MIMICRY, in zoology, the deceptive and advantageous resemblance presented by defenceless and edible species of animals to other species of animals living in the same locality, which are harmful or distasteful and are consequently avoided by all or by a majority of the enemies of the class to which the mimetic and usually the mimicked species belong.
Still more rarely mimicry exists between totally unrelated species like caterpillars and snakes or spiders and snails.
The principle of protective resemblance, for which the term mimicry, as above defined, was originally employed, was first explained by H.
Hence the resemblances belonging to the first category are commonly termed "Batesian mimicry," and those belonging to the second category " Mullerian mimicry," or more properly " Mullerian resemblance."
The difference between the two phenomena is essential and evident; but without experimental information as to palatability it is impossible to know with certainty to which of the two a particular case of mimicry is to be assigned.
Over and over again extended knowledge on this point and inferences drawn from other facts have shown the certainty or probability of examples of mimicry being in reality " Mullerian," which were previously accepted without question as " Batesian."
A simple illustration will serve to explain these two aspects of mimicry and to show the advantage in the struggle for existence that mimicry confers upon the species concerned.
So far as our information at present extends the resemblance between these two insects is a simple case of mimicry in the Batesian sense of the word.
But if it be discovered, as is possible, that the drone-fly is also inedible, the mimicry must be ascribed to the Mullerian category, and the reason for it becomes less evident.
This type of mimicry has been well defined by Professor E.
Since belief in the adequacy of the two theories, above outlined, to account for the facts they profess to explain, depends ultimately upon the testimony that can be brought forward of the usefulness of warning characters, of the deception of mimicry and of the capacity for learning by experience possessed by enemies, it is necessary to give some of the evidence that has been accumulated on these points.
The results of this experiment with the baboon and of those with the birds are precisely what would be expected if the theory of mimicry is true.
The term mimicry has also been applied to resemblances of a different kind from the two enumerated above - resemblances, that is to say, by which predaceous species are supposed to be enabled to approach or mix without detection with animals they prey upon or victimize in other ways.
This phenomenon is termed " aggressive mimicry " as opposed to the Batesian and Mullerian phenomena, which are termed " protective mimicry."
A few possible cases of aggressive mimicry are enumerated in the following summary of some of the recorded cases of mimicry in different classes of the animal kingdom; but the phenomenon is of comparatively rare occurrence, and the supposed instances may be susceptible of other interpretations, excluding them altogether from mimicry, or bringing them under the Batesian or Miillerian interpretation of the phenomenon.
Among mammalia there are no certain cases of mimicry known.
A few cases of mimicry have been recorded in birds.
Some observations, however, of Guy Marshall on the inedibility of certain birds suggest that the resemblance between cuckoos a'nd hawks on the one hand and cuckoos and drongos on the other may be susceptible of another explanation in full agreement with the theory of mimicry as propounded by Bates.
One of the most perfect cases of mimicry in birds is presented by a Madagascar thrush or babbler (Tylas eduardi), which resembles feather for feather a shrike (Xenopirostris polleni), from the same island.
Analogous cases are supplied by the mimicry that exists between some of the orioles (Mimeta) and the friar-birds (Philemon or Tropidorhynchus) of the Austro-Malayan Islands.
Apparently the only instances of mimicry known amongst reptiles occur amongst snakes; and in all the cases quoted by Wallace harmless snakes mimic venomous species.
Considering, however, the numbers of venomous and innocuous snakes that occur in most tropical countries, it might be supposed that mimicry in this order of reptiles would be of commoner occurrence than appears to be the case.
It is amongst Arthropods, however - and especially amongst insects - that mimicry, both Batesian and Miillerian, occurs in greatest profusion and perfection.
Some cases of genuine mimicry, however, are known in the order.
This may, however, be an instance of Miillerian rather than of Batesian mimicry, the beetle being itself inedible; for Shelford has stated his conviction that the Bornean representatives of the sub-family (Clytinae), to which Clytus arietis belongs, are all highly distasteful and are warningly coloured, as are members of this sub-family from other parts of the world.
In the Hemipterous group of the Rhynchota ant-mimicry is illustrated by the larva of a British species of Reduviidae (Nabis lativentris) in which the forepart of the abdomen is furnished on each side with a patch of white hairs leaving a central narrow dark portion in imitation of the waist of the ant; and also by an East African species (Myrmoplasta mira) which in its general form exhibits a close resemblance to an ant (Polyrrhacis gagates) which occurs in the same neighbourhood.
Hence it is probable that this case of mimicry is purely of a protective and not of an aggressive nature and serves to save the flies from destruction by insectivorous enemies.
The same explanation no doubt applies to the mimicry, both in Borneo and South Africa, of hairy bees of the family Xylocopidae by Asilid flies of the genus Hyperechia, and also to other cases of mimicry of Hymenoptera as well as of inedible beetles of the family Lycidae by Diptera.
Numerous other cases of mimicry between Diptera and Hymenoptera might be cited.
The Lepidoptera furnish more instances of mimicry, both Batesian and Mullerian, than any other order of insects.
Instances of ant-mimicry in this order are sometimes confined to the larval stage.
A parallel case of mimicry exists at Singapore between the larva of a Noctuid moth and the common red tree-ant (Oecophylla smaragdina).
Another instance of mimicry affecting the larval form is supplied by the moth Endromis versicolor, the caterpillars of which resemble the inedible larvae of saw-flies.
Of the multitudes of cases of mimicry between different species of Lepidoptera, a few only can be selected for description.
Bates offered no satisfactory explanation of the resemblance between these two genera and others of the same protected sub-families; but he did not hesitate to ascribe the resemblance to them presented by the Pierine, Dismorphia (Leptalis) orise, to mimicry, believing Dismorphia to be unprotected and noting that it departed widely in the matter of coloration from typical members of the sub-family to which it belongs.
Although mimicry in the Lepidoptera has been carried to a greater extreme in South America than in any other country of the world, remarkable instances of it have taken place in the Ethiopian and Oriental regions.
The second noteworthy phenomenon is the mimicry of more than one protected species by members of a single species.
This is a not uncommon occurrence, and in the case of Batesian mimicry the explanation is probably this.
Were this to take place the purpose of the mimicry would be abortive, because enemies would probably not refrain from slaughter if even every alternate capture proved palatable.
It is probable that one explanation - namely, that of protection - covers all cases of ant-mimicry; and this explanation lies in all probability in the immunity from the attacks of most insectivorous enemies that ants enjoy, and especially from predaceous wasps of the family Pompilidae which annually destroy thousands upon thousands of spiders to feed their larvae; and since more than one observer has testified to the fear and abhorrence these wasps have of ants, it is needless to look farther for the benefit ant-mimicry is to spiders.
In the above-cited historical instance of mimicry amongst some South American Lepidoptera which formed the foundation of Bates' theory, species of butterflies, belonging to the Ithomiine genus Itura and the Danaine genus Thyridia, both unpalatable forms, resemble each other.
The significance of this phenomenon, as already stated, was first explained by Fritz Milller; but although the term " Mullerian mimicry " has been assigned to this and similar instances, they are not strictly speaking cases of mimicry at all but of warning coloration.
An important phenomenon connected with insect mimicry is the convergence of several species in the same area towards a common type of coloration and shape, exhibited by one or more than one protected form.
Since many of the insects of the order Hemiptera are distasteful, the mimicry of the bug (Megapetus) is in this case probably Mullerian or synaposematic; the grasshopper (Myrmecophana), on the other hand, is probably edible and the mimicry is Batesian or pseudaposematic. This is a simple case consisting of a small number of component species.
The mimicry of these insects therefore is synaposematic; but some, at all events, of the flies like the Bombylid Exoprosopa umbrosa, probably form pseudaposematic elements in the group. Into another category Hymenoptera enter not as models but as mimics, the models being inedible Malacodermatous beetles mostly belonging to the genus Lycus and characterized by orange coloration set off by a large black patch upon the posterior end of the elytra and a smaller black spot upon the thorax.