This is a not uncommon occurrence, and in the case of Batesian mimicry the explanation is probably this.
The Lepidoptera furnish more instances of mimicry, both Batesian and Mullerian, than any other order of insects.
Of the multitudes of cases of mimicry between different species of Lepidoptera, a few only can be selected for description.
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.
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."
Numerous other cases of mimicry between Diptera and Hymenoptera might be cited.
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.
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.
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.
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.
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."
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.
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.
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.
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.
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.
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.
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.
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.
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.