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N most of the larger and preparation may be cultivated, or rather kept
rarely beyond low- vases of sea-water, in a cool and shady position,
ON MIMICRY IN DIPTERA.
W HEN will some of our entomologists who have beauty, the micro VV collected and studied nearly every Lepidop
scope reveals its terous insect known to inhabit Great Britain, devote extreme elegance. It is discovered forming dense even a small amount of attention to the other orders globular tufts two or three inches long, about the of insects? The Coleoptera certainly have received thickness of a horse hair at the base, expanding in a fair amount of attention, but the Diptera have parallel branches pointing upwards, somewhat rigid. been sadly neglected. Microscopically, the frond is found to be fili And this unpopularity is scarcely deserved by them, form, and articulated, repeatedly forked, marked for albeit they do not possess the brilliant colouring externally with striæ, interrupted at the joints, and and large dimensions of some butterflies, many of generally the structure is disposed in a series round a them are extremely elegant; while their points of central cylindrical internal cavity; the colour brown- interest will be found to be almost more varied and pink-purple-black when dry. Although the mode more striking than those of the Lepidoptera. of propagation has until recently been somewhat Any who would take the trouble to catch and obscure, it is ascertained that there are two kinds of pin out the Diptera found in their neighbourhood fructification, in distinct plants. Tetraspores which might possibly discover new habitats, if not new at maturity divide into parts, generally four, or more ; species; in any case, such a collection would greatly and antheridia, oblong bodies, rounded at the extre assist our knowledge of the distribution of the various mities, produced in fascicles on the summits of the species. ramuli, and subdivided into parts. The drawing Those who travel miles to find a rare moth are shows the apices of a frond with these reproductive usually only going over old ground that has been organs. They are so extremely abundant in the early visited by scores of collectors bent on the same spring months, as to give a very conspicuous yellow errand, and instead of increasing our knowledge of colour to the tufts on which they are produced. the insects, are only lending their small aid to the Minute marine algæ, for microscopical observation extermination of the species.
No. 251.- NOVEMBER 1885.
The subject of this paper, is, however, one which were only with difficulty to be distinguished from one opens up a wide field for observation, and in which another, so that it is beyond doubt that, the scorpion much valuable information might be obtained even fly, of which the body is rather hard, not being a very by those who have not sufficient leisure to form a palatable meal for birds, the Leptis takes advantage local collection. .
of its similarity with this insect to escape being eaten, Many of the species mentioned below are among it being a softer bodied insect and therefore better our commonest insects, while other not rare flies food for birds. The fact that the Panorpa was by may prove on observation to be cases of mimicry. far the more abundant insect of the two is in corro
One of the first things that a beginner at “fly boration of this. catching” would notice is the extraordinary similarity The species of Bombylius, although called humblebetween some of these insects and the bees and bee flies by some entomologists, do not much resemble wasps. In showing my Diptera to friends, I any of our British species of Bombus. They feed on notice that they constantly remark, “ That is a bee, the juice of flowers, as does the humming-bird surely ?” or “ That is a wasp?” And the editors of moth. “ Little Folks” fell into the same error some years Though rather like some Apidæ, my observations since, for I have before me a volume in which, among would lead me to give my opinion against their being other instructive paragraphs for the young, I find cases of mimicry, but perhaps that may be because I one on “Busy Bees,” accompanied by a very fair have not found the mimicked insect. As they dart woodcut of several flies including Stratiomys, Tabanus, | about quickly, they may not need protection. and even Tipula, but without a single bee or wasp But it is among the flies of the family Syrphidæ among them.
that we find the most singular resemblance with That the Romans and other ancients evidently Hymenoptera. Who has not seen the ubiquitous made a very similar mistake, owing to this resem drone fly (Eristalis tenax) buzzing on the window blance, we shall see presently.
pane, or, in late autumn, crawling wearily along the Beginning with the Stratiomyidæ, we find among sill, and who has not mistaken it for a bee (Apis the species of Stratiomys a considerable similarity to mellifica)? I have but to go into the garden and bees, especially when flying.
watch a patch of flowers; there, beside the numerous My specimen of S. furcata was captured under the bees which come to gather honey, I am sure to find impression that it was probably a bee, especially as some of these flies. And I have to look twice before the insect, when settling on a plant, folded its wings pronouncing them to be flies. If I take one of them over the back in the same manner as do the bees. in my fingers, some non-entomological friend will
Asilus crabroniformis (SCIENCE-Gossip, 1876, certainly exclaim, “Take care it does not sting p. 156, Fig. 85) is so called from its having rather
you !" the habit of a hornet when on the wing, but when Baron C. R. Osten Sacken has pointed out that captured, it is seen to be so entirely unlike a hornet the belief, universal among the ancients, that bees that, without further evidence on the subject, I can originated from carcases of dead animals (oxen, &c.), scarcely believe it to be a case of mimicry. Much undoubtedly owes its origin to this resemblance. more is Laphria ephippium, another insect of this
| That belief is often mentioned in their writings (for family, like a bee. This fly occurs in many places instance it is alluded to at great length in Virgil's on the Continent.
“Georgics,” book iv. verses 285 et seq.), and has been In the Leptidæ, I observed a remarkable case of reproduced by the earlier modern writers, such as undoubted mimicry, the mimicked insect being in Aldrovandi (“De Anim. Insectis," p. 58, edit. 1602), this case, not a Hymenopteron, but a Neuropteron. and Moufet (Theatr. Insect., p. 12). I was walking along a lane in Warwickshire one
The rat-tailed larvæ of Eristalis thrive in putrefying June, some two or three years back; the scorpion animal matter, and the very natural explanation of fly (Panorpa communis), a neuropterous insect, the superstition is that the perfect insects were familiar to all who live in the country, was ex mistaken for bees. tremely abundant, the hedges swarming with them, Eristalis æneus, as well as Cheilosia chrysocomus and after netting one or two of these, I thought I closely resemble some of the Andrenidæ, both in had captured another, but on examining it, I found colouring and in general appearance. it had two wings instead of four, and was easily E. floreus, on the other hand, takes after the wasps recognised as Leptis scolopacea. I have placed the in its colouring ; some specimens of this fly would be two insects in my collection side by side, and even mistaken for wasps by any but an entomologist. when compared closely they possess considerable In that respect it is not singular, for several similarity with the wings folded.
Syrphidæ are somewhat wasp-like when flying, but In both, the wings are mottled with brown spots, perhaps the best imitation of a wasp is that afforded the legs are longish and rather thin, and the abdomen by Chrysotoxum arcuatum and C. octomaculatum. The is also slender.
latter species is rare in England, but at Heidelberg But when settling on a hawthorn bush, the insects | some few summers past, when wasps (Vespa vulgaris)
were very troublesome, there was rather an abundance of C. octomaculatum. The yellow and black markings on the abdomen, the wings with a brownish tinge, especially along the anterior margin, and even the long antennæ, all combine to produce an appearance very like a wasp. Owing to this fly being about when wasps are plentiful, it doubtless obtains some protection from this similarity.
Still more closely does Volucella bombylans mimic several species of humble bee (Bombus), moreover it is subject to considerable variety, and each of the different forms exactly reproduces the colouring of a corresponding type of Bombus.
In Britain we have two varieties, distinguished by many entomologists as different species, V. bombylans and V. plumata.
Now in the former the thorax and abdomen are black, the thorax is covered with black hairs, while the tip of the abdomen is clad with hairs of an orange-brown colour. This is precisely the colouring of Bombus lapidarius and B. rupestris. In the latter, most of the thorax is clothed with yellowish hairs. There are patches of yellow on the sides of the abdomen near its base, while its tip is covered with whitish hairs-an arrangement of colour almost identically the same as in Bombus lucorum, B. collinus, B. pratorum and some others.
So much for the British forms of the fly, but it does not confine itself to imitating the colouring of only two kinds of Bombus. Baron Osten Sacken has kindly sent me a copy of a short review by him * of a Russian work by J. Portchinsky on the Diptera of the Caucasus resembling Bombus. M. Portchinsky finds that in the Caucasian mountains the humblebees (Bombus eriophorus, niveatus, Caucasicus) are all characterised by the prevalence of white hairs on various parts of the body. The plain black and orange coloured humble bees, like B. lapidarius, are entirely absent. It is therefore remarkable that in this region the black and orange variety of Volucella bombylans is absent, as though it had no cause for existing, while in its place a variety (V. bombylans, var. Caucasica) is found, which is unknown elsewhere in Europe, and in which the thorax and the base of the abdomen are clad with white hairs, after the manner of the humble bees of the Caucasus. A translation of M. Portchinsky's work is much to be desired.
All entomologists are aware of the great resemblance which obtains between the hornet clearwing moth (Trochilium apiforme) and the hornet (Vespa crabro). Not less striking is the resemblance to the latter insect of a fly (Milesia crabroniformis) which, though not found in England, is abundant in many parts of France and Italy. It is exactly the size of an average hornet, the colouring of the thorax abdomen and legs is very nearly the same, while even the wings are of a brownish tinge, similar to that of the hornet's wing.
“Wiener Entomologische Zeitung," i. (1882), Heft 9.
When first I saw one of those flies buzzing round a trellis at Mentone some seven years ago, I captured it under the impression that it was a hornet.
At Cadenabbia, on the Lake of Como, Milesia crabronifornis was a common insect, and although it was doubtless protected from the attacks of birds by its likeness to a hornet, it sometimes suffered for its resemblance, for I have seen the natives try to kill it, and no amount of explanation could shake their firm conviction that it was a hornet.
Thus in one family of Diptera we have flies mimicking several types of common Hymenoptera; the bee, the wasp, the andrena, two forms of humble bee, and the hornet. The similarity is so great in these instances, particularly when the insects are alive and in motion, that no doubt can exist that they are cases of protective mimicry.
There are, however, other instances of resemblance between Diptera and Hymenoptera on which it is not so easy to decide whether they be cases of mimicry or not.
Before concluding, I should like to mention two that have come before my notice. Comparing a specimen of Myopa ferruginea with a species of Nomada (probably N. lateralis), I was at once struck by their general similarity, and remarked that even the whitish patches on the abdomen of Nomada were represented by light spots on the body of Myopa. The likeness between these two insects has previously been observed by entomologists. The other case which occurred to me only just lately, is the resemblance between Mesembrina meridiana and some of the Anthophoræ, as A. retusa.
The fly, one of the Muscidæ, has rather curious colouring, it is entirely black, with the exception of the wings, which, though pale grey towards the tips, are of a brilliant orange-yellow near the base. The Anthophoræ are black, but collect a quantity of pollen on their hind legs. They are about the size of M. meridiana. Now is it not highly probable that the yellow at the base of the wings of M. meridiana reproduces, when the insect is flying, the appearance of the pollen on the tibiæ of Anthophora ?
Whether the last two are cases of protective mimicry, could only be ascertained by open-air observation. If the flies are frequently seen associated with the insects they copy, or are found in similar places and seasons, we may fairly suppose them to be so. With regard to the Myopa, I fancy I have caught it and Nomada near the same spot, but as I knew scarcely any entomology at the time, and was quite a young boy, I may easily be mistaken. Were Diptera studied a little more, we should doubtless find numerous other cases of mimicry among them, including some that are now quite unknown. Let us therefore earnestly hope that some entomologists will employ their leisure in further investigations on this most interesting subject. G. H. BRYAN.