On defining ‘mimicry’
MALCOLM EDMUNDS
Biology Division, Preston Polytechnic, Corporation Street, Preston, PR 1 2 T Q
Vane-Wright ( 1980) argues that stick-mimics, leaf-mimics etc. should be
regarded as examples of crypsis and not as examples of Batesian mimicry which I
have done in the past (Edmunds, 1972, 1974, 1976). The problem centres on the
definition of mimicry. In 1974 I followed Wickler (1968), who concludes that
mimicry is the imitation by one animal (the mimic) of a signal produced by a
second animal (the model) that is of interest to a signal receiver which is then
deceived into confusing the two signals. One problem with this definition is that
Mullerian mimicry is excluded from mimicry since no deception is involved. For
Batesian mimicry I was able to modify Wickler’s definition: “Batesian mimicry
occurs when a predaceous animal, which avoids eating one animal producing a
particular signal, is deceived into avoiding a second animal which produces a
similar but counterfeit signal” (Edmunds, 1974). It was not at all easy to decide,
following this definition, whether stick-like insects and leaf-like insects should be
regarded as examples of crypsis or of Batesian mimicry; after considerable
indecision and redrafting, I ended by including them under Batesian mimicry on
the grounds that they precisely resemble an inedible object (e.g. a lea0 rather
than have a general resemblance to a green background, which would be crypsis.
However, following Vane-Wright’s improved definition of mimicry (VaneWright, (1976, 19801, stick-like insects are cryptic because they produce signals of
no interest to a predator, whilst mimics produce signals which are of interest to a
potential predator. If I were writing Defence in Animals today I would probably
follow Vane-Wright’s recent definition and consider stick-like insects under the
heading of crypsis.,
But Vane-Wright’s definition of mimicry still leaves problems. Many
nudibranch molluscs rest on and resemble sponges, polyzoans or hydroids so
presumably they are cryptic. But the dorid Jorunna has spicular papillae, rhinophore sockets and gills which closely resemble the texture and openings of the
sponge on which it feeds; the eolid Tergtpes has papillae which resemble the form
and arrangement of hydranths on a hydroid; the eolid Aeolidia can curl up and
resemble a partly contracted sea anemone and the eolid Fiona has the deep blue
colour and appearance of part of the siphonophore Velella. Are these adaptations
cryptic or mimetic with respect to a predatory fish? Following Vane-Wright, if the
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M. EDMUNDS
coelenterate (or sponge) is of no interest to the fish, then it is crypsis, but if the
tish actively avoids the coelenterate because of its nematocysts, then it is mimicry.
Unfortunately we do not know what a fish perceives when it swims past a sponge:
to one species it may be mere environmental noise, whilst to another it may be
something to respond to. The final complication is that all these nudibranchs
have other defences (spicules,chemicals and nematocysts)so they themselves may
be distasteful to some potential predators and hence be Mitllerian mimics.
There are other anomalies. The fish Siphamia may aggregate in close formation
and resemble the sea urchin Astroprga (Fricke, 1970). Presumably, predatory fish
mistake the shoal for an urchin but do they avoid it because it is ignored as noise,
or because it is recognized as something nasty? We do not know, so we cannot tell
if‘ this is crypsis or mimicry. De Ruiter’s jays could not distinguish stick-like
caterpillars from twigs until they accidentally trod on one. The question then is,
was the signal of the caterpillar of no interest at all (crypsis),or was it of possible
interest as an object to grip with the claw, in which case it becomes mimicry.
My aim is not to destroy Vane-Wright’s argument, which is based on an objective definition of mimicry, but to point out that some anomalies still occur,
perhaps because we can very often only guess at how the operator (predator)
perceives a signal. And it is just not possible to fit all examples into a neat scheme
of definitions such as the different forms of mimicry proposed by Vane-Wright
in 1976. Defining terms helps us to ask the right questions and to understand
principles but it is not always sensible to regard definitions as being 100% rigid.
Even if stick- and leaf-like insects are now considered as extreme cases of crypsis
rather than as examples of Batesian mimicry, it is still, I hope, acceptable to call
them stick- and leaf-mimics, using the s u f i simply to imply a very
precise resemblance.
Finally, there is surely nothing new in this debate: Cott ( 1940) must have had
the same problem but he adopted yet another solution: he put these anomalous
examples in a category of ‘special resemblance’. Perhaps he was more perceptive
than we are today and this will yet prove to be the most widely accepted solution.
REFERENCES
COlT, H. B., 1940. Adaptive Coloration in Animals: 508 pp. London: Methuen.
EDMUNDS, M., 1972. Defensive behaviour in Ghanaian praying mantids. ZoologicalJoumul ofthe Linnean Society,
5 1 : 1-32.
EDMUNDS, M., 1974. Dc/cnce in Animals: 357 pp. Harlow: Longman.
EDMUNDS, M., 1976. The defensive behaviour of Ghanaian praying mantids with a discussionof territoriality,
Z~ologicalJ O U Pjthe
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Linn~anSoriety, 58: 1-37.
FRICKE, H. W., 1970. Ein mimetisches Kollektiv-Beobachtungen
an Fischschw2nnen, die Seeigel
nachahmen. Marine Biology, 5: 307-314.
VANE-WRIGHT, R. I., 1976. A unified classification of mimetic resemblances. BiologicalJournul ofthe Linnean
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VANE-WRIGHT,R. I., 1980. On thedefinitionofmimicry. B i o l o ~ c ~ J ~ r n u l o f t ~ L i n n e a n S o13:
c i 1-6.
c~,
WICKLER, W., 1968. Miminy in Plants and Animals: 255 pp. London: Weidenfeld & Nicholson.