Organic Evolution in terms of the Implicate and Explicate Orders.

Part XXVI :

The evolutionary diversification in the Order Diptera.

Extensive intrusion of metatypic characters into the order- and family-groundplans in epizoic Diptera (Braulidae, Hippoboscidae, Nycteribiidae, and Streblidae).


In Diptera there are a number of families of which the representatives are epizoic, which means that they live on the bodies of other animals which can be insects, birds, or mammals. So we have the Braulidae of which the imagines live on the body of honey-bees, the Hippoboscidae that live on birds or mammals, the Nycteribiidae and Streblidae, which live exclusively on bats. All these are families of the Order Diptera, and while the Braulidae can considered to be acalyptrate cyclorraphic flies, the other families belong, as far as can be determined, to the calyptrate cyclorraphic flies. Many of them are wingless. And, except the Braulidae, they do not lay eggs but fully-grown larvae which directly pupate.

As a result of their peculiar way of life these diptera have changed to such an extent that most of them do not look like flies at all. And this not only because many of them have lost their wings, but because their entire body structure (their organization) has changed dramatically in accordance with their epizoic way of life. It is because of these heavily transformed organizations, having become totally different from almost any other dipterous organization (and, moreover, totally different from each other as well) that new families are erected for them, or even new supra-orders. It is, however, clear that they represent peculiar off-shoots of existing or extinct families originally consisting of normal diptera, that is to say, certain species of these original families have found new and peculiar environments (for example bee communities), and in them new ecological niches to live in. As a result of adaptation to these highly strange and new habitats and way of life the species underwent intense transformations, so intense, that is, that they can be recognized as being in fact certain diptera only upon very close scrutinization. So in the present context we consider the 'families' Braulidae, Hippoboscidae, Nycteribiidae, and Streblidae not as separate families in their own right, but as deviant off-shoots of families originally consisting of normal diptera. And it is the groundplan of one or the other of those original families that we are speaking of in what comes next. So, said in terms of groundplans (prototypes) we can describe things as follows :  In each of the mentioned epizoic group of diptera the family-groundplan, and even the order-groundplan (the groundplan "Diptera"), has evolutionarily been, to a very great extent, 'over-written' (over-formed) by metatypic characters, that is, in addition to the emergence of new metatypic characters, many prototypic characters of the family- as well as of the order-groundplan have been replaced by metatypic characters mainly of an adaptive nature. So there is little left of the prototypic characters of the order- and family-groundplans, meaning that these groundplans have become in a stronger degree implicit than they already were, as a result of the far-reaching demands of adaptation. In the Braulidae, for example, not only the wings are lost, but also the halteres, and, in addition to that, the 'fly-shape' of the body.
After having considered all this, we can say that the characters of one or the other of the mentioned epizoic groups of diptera that are adaptive to this or that type of epizoic life are metatypic characters of the groundplan of the  original  family (this groundplan including the dipterous groundplan) from which the epizoic group (the 'new' family) has descended. But these same characters must be interpreted as being  prototypic  with respect to the new family, that is, as having their place among the prototypic characters of the new family, into which the original family had been transformed. This means that we have to do with a new groundplan having evolved from another as a result of a transgression from one ecological niche into another, while in most cases, as we have seen, the appearance of a new groundplan has to do with the noëtic derivation of it, in the Implicate order, from another groundplan on the basis of their respective stability fields, and as such not a matter of the Explicate Order because generally groundplans do not have special ecological significance.

The morphology and ecology of the epizoic diptera are so peculiar that they constitute a great challenge to evolutionary theory :  Any such theory that respects itself must be able to at least describe them evolutionarily in its own terms. And of course this also applies to our own theory involving Implicate and Explicate Orders. And, to begin with, it is clear that the morphologies, adaptations, and feeding habits of these epizoic diptera cannot be described (exclusively) in terms of random mutations and natural selection, because too many necessary and integrated adaptations are involved in each group of these diptera.
Let us now, one after the other, describe and comment on the four mentioned groups -- 'families' -- of dipterous epizoons.

Braulidae  (Bee-lice)

Sometimes on the body of our honey-bees one can find pinhead-sized shiny-brown diptera which look a little like mites. It is the bee-louse,  Braula  caeca NITZSCH.  The essential characteristics of these strongly transformed diptera are :  winglessness, absence of halteres, strong legs, very small inconspicuous complex eyes, a relative narrow thorax, and a wide weakly curved abdomen. See next Figure.

Figure 1 :  This micromount of the bee-louse (Braula  caeca) clearly shows the absence of wings and the comb-shaped claws of the strong legs.
(After SCHUMANN, in Neue grosse Tier-enzyklopädie, 1971.)

That this animal is an acalyptrate fly (Diptera, suborder Cyclorrapha), and not some other insect as the name might suggest, is evident from the body-structure, the presence of the frontal sac, that is, the ptilinum (which, on inflation serves to thrust off the anterior end of the puparium at the time when the contained imago is ready to emerge and to force the fly through soil, etc.) and the ptilinal suture, the structure of the copulation-device, and the developmental stages (larva, pupa). However, its precise place in the taxonomic system of the Diptera is not known for certain. Some features point to the Borboridae or the predatory Chamaemyiidae (both acalyptrate flies). Certain is that they do not belong to the Pupipara, because the females lay eggs (not larvae or pupae) and the larvae -- which are normal maggot-like -- are free-living.
The eggs and larvae are to be found on the inner surface of honey-cells. The young larva of  Braula  tunnels into the wax cap of the cell, and may pass from one cell to another. The larva swallows wax grains and some pollen, and apparently digests the wax with the aid of intestinal micro-organisms in the same way as the wax moth,  Galleria  mellonella.  One of the main reasons why it is thought that  Braula  is related to the Chamaemyiidae is that the mouth-hooks of the larva are similar, and suggest that perhaps  Braula  once had a carnivorous ancestor. There are three larval instars, in the typical way of the Cyclorrapha, and the pupa is formed within the last larval skin, though this is not hardened into the customary barrel-shape. The larva has already weakened a part of the overlying cell-cap, and when the adult insect inflates its ptilinum, this forces an opening through which the insect can crawl.
The adult  Braula  is said to cling mostly to the junction between thorax and abdomen of the bee, but to move towards the head when it wants to feed, and there to take saliva from the mouthparts of the bee. This reminds us of the many insects that take food from ants, and indeed none of the evolutionary devices of  Braula  is unique. The interest of this fly is in its lonely evolution, which raises again the familiar question :  how did it get started in this direction, and why have not others done the same? (OLDROYD, 1964, p. 183).
We shall ty to answer this question, but only in a general way.
The original family from which the Braulidae (containing only  Braula  caeca) branched off might be conceived of as the acalyptrate family Chamaemyiidae. Their larvae prey on plant-lice and scale-insects, and move about the colony feeding. The adult flies are said to suck honey-dew from the surface of the leaves and stems, and it is possible that the larva, too, takes a mixed diet. Some Chamaemyiid larvae live in the galls of other flies.
A bee colony can be considered to be a special environment (for other animals). A number of Chamaemyiid flies belonging to a given species, say the species S, might, during their normal activity, come within the range of this environment. This can be the case in several places involving a number of individuals of species S. If there are no special interactions of these Chamaemyiid flies with elements of this environment, nothing will happen. But if there take place genuine interactions with these elements on a more or less regular basis, for example if the flies let themselves carry away by the bees by clinging to their body, and in this way end up in the bee colony (from which they can return in the same way), or if the flies can get hold of some food carried by the bee, then they have discovered one more potential ecological niche of the family Chamaemyiidae from its intrinsically determined set of potential ecological niches.  The earlier divergence of the family Chamaemyiidae, having already resulted in the existing different species of the family, expresses the successive discovery and subsequent occupation of the different potential ecological niches already intrinsically defined by the groundplan of the family. The described interactions with elements of the new environment reveal yet another member of the groundplan's set of potential ecological niches. The qualitative content of this new niche will be injected into the Implicate Order where it will exist as a noëtic entity and noëtically react with the noëtic content of the groundplan of the family Chamaemyiidae. The reaction-product will then be projected into the Explicate Order at the appropriate places (where the interactions took place, and where-only projection is possible) where it is experienced as a process of evolutionary adaptation of a part of the original Chamaemyiid species S to the new ecological niche resulting in the transformation into Braulids, that is, into bee-louses. In this process, consequently, the original Chamaemyiid species has splitted into two, one of which is still the original species while the other is a new species. But this new species is in such a degree morphologically transformed that it is legitimate to place it in a new family, the Braulidae (and even, according to ROHDENDORF, in a new infraorder, the Braulomorpha).

The next three families of epizoic diptera (together constituting the "Pupipara") have larvae that almost have no independent life, each being fed individually in its mother's womb, and becoming a pupa as soon as it is liberated. The adult flies do all the feeding, and subsist on a pure diet of blood, living as external parasites of mammals and birds. They are very considerably modified in structure to suit this way of life, and seldom or never leave their host. Although the Pupipara share the laying of fully-formed larvae instead of eggs they are apparently not a natural group in the sense of one special taxon.
It is instructive to remark that we can interpret flies that suck blood from other animals, such as mosquitoes, black-flies, horse-flies, and tsetse-flies, but that, as do these flies, only temporarily attach themselves to their hosts, as representing a first evolutionary stage of ectoparasitism or epizoic life style. This does, however, not necessarily mean that epizoic flies like the Pupipara actually have descended from such free-living but occasionally blood-sucking flies. Interesting in this respect is the following (BRUES, Insects, Food, and Ecology, 1946) :  Numerous cases of small midges belonging to  Ceratopogon  and other genera of the family Ceratopogonidae (biting-midges) have come to light in which the adults have been found sucking the blood of other insects. One species of  Forcipomyia  attaches itself to the wing veins of lacewing flies  Chrysopa  (Order Neuroptera) and a Danish  Ceratopogon  occurs on the wings of moths with the proboscis inserted into the wing veins. A very interesting account of a number of species belonging to several genera has been given by MacFie (1932), especially of some that occur on the wings of dragonflies where they feed by inserting the proboscis into the veins. Some of these lack the tarsal claws, clinging to the wings of the host by means of the remarkably modified empodium at the tip of the last tarsal joint. See next Figure.

Figure 2 :  A blood-sucking midge,  Pterobosca  adhesipes,  which attaches itself to the wings of dragonflies.
A -- Adult in position on the wing of  Agrionoptera.
B -- Tip of tarsus, showing the sucker-like process.
(After BRUES, 1946)

The next account of this group and the three families that are meant by it is taken from OLDROYD,  The natural history of flies, 1964, pp. 229.
There are three families of Pupipara :  Hippoboscidae feed upon many different mammals and birds.  Streblidae and Nycteribiidae are confined to bats. It appears most probable that these three families came from at least two different ancestors, Hippoboscidae perhaps from flies living in birds' nests, and Streblidae and Nycteribiidae from flies that bred in the roosts of cave-dwelling bats. Hippoboscidae have nuch in common with tsetse-flies which also drop fully fed larvae, and have adults that feed only on blood. The obvious difference is that tsetse-flies have retained their independence, and only visit their victims when they want to feed, whereas Hippoboscidae spend their adult lives on their hosts. The two families [Hippoboscidae and tsetse-flies] have enough in common to suggest that in the remote past they might have arisen from a common ancestor among the muscoid flies. In particular, their piercing proboscis is formed from the stem of the labium, and the labella, which are spongy lobes in house-flies, are hard, small, and insignificant in Hippoboscidae, whereas in Streblidae and Nycteribiidae it is the labella themselves that are drawn out into a piercing organ.
[We will now discuss the biology of the three families one after another -- following OLDROYD -- and will add a generalized discussion about their evolutionary origin.]

Hippoboscidae  (louse-flies, keds)

There are about a hundred species of Hippoboscidae scattered throughout the world, and almost everything of interest about them concerns the adult flies. They are always flattened dorso-ventrally, with a tough, leathery appearance, and strong legs equipped with long, curved claws. They are called 'louse-flies' when they occur on birds, and 'keds' on mammals, the latter especially the wingless species.

Figure 3 :  The epizoic swift louse-fly,  Crataerina  pallida,  possesses strongly developed claws, and vestigial wings. The object below is a puparium of this species.
(After SCHUMANN, in Neue grosse Tier-enzyklopädie, 1971.)

The adaptation of these flies to a parasitic life has evidently been going on for some time, and is very complete, affecting every detail of their external appearance. The flattened shape and strong, spider-like legs enable them to move quickly about on the skin of the host, pulling themselves along by grasping the hairs or feathers, with a crab-like motion.
The thorax is a solid box with its component sclerites more firmly united than in most flies, but the abdomen is soft, and mainly membranous. The sclerites of the abdomen are reduced in number as well as in size, and show a progressive reduction from the primitive to the advanced members of the family, and more reduction in females than in males. The eyes are also smaller than they are in flies that live a free life in the open air, but not as greatly reduced as they are in the other two families of Pupipara.
Most Hippoboscidae have wings, and many fly well. As to the wings of some species, see next Figure.

Figure 4 :  Wings of the epizoic dipterous family Hippoboscidae (louse-flies).
Upper image :  Lipoptena  cervi L.  Length 5 mm.
Central image :  Hippobosca  camelina Lch.  Length 10 mm.
Bottom image :  Ornitheza sp.   Length 4 mm.
(After ROHDENDORF, 1951)

Broadly speaking, those that fly actively are found on a variety of hosts, and few, if any, are physiologically confined to one host in the sense of being unable to tolerate any other blood. As with fleas, and perhaps other parasites, it is really the host's habitat to which the parasite is adapted, and it will accept other hosts if they occur in similar surroundings. So the number of hosts available to any particular Hippoboscid is determined by the type of habitat.
Crataerina  (Crataerrhina) (Figure 3) and  Stenepteryx  are Hippoboscids with narrow and pointed wings, or very short ones, which in either case cannot be used for flight. This sacrifice of the powers of flight is linked with the fact that these flies live exclusively on swallows, martins, and swifts, birds that spend most of their time on the wing, and which return year after year to the same nesting colonies. It would therefore seem reasonable to say that loss of flight is an advantage, reducing the risk of separation from such a high-speed, streamlined host. The process of reduction has gone even further in more tropical members of this group.  Myiophthiria  in the Old World, and  Brachypteromyia  in the New, have ludicrous little pads, with only a caricature of wing-venation, like the wings of fairies in a pantomime. Unfortunately for theory,  Ornithomyia  biloba  and perhaps one or two others also live on swallows, but have the fully winged mobility of their genus. Once again we wonder why one insect has slowly evolved what seems to be an elaborate adaptation to a particular way of life, while another insect does the same job without adaptation. See next Figure for a winged  Ornithomyia.

Figure 5 :  Ornithomyia  avicularia L.  (Hippoboscidae).  5 mm.
(After OUDEMANS, from SENDEN, Muggen en Vliegen, Part 26 of Wat leeft en groeit)

[Here it is again evident that organic evolution is not a process exclusively focussed on biological improvement. The evolutionary process is mainly focussed on creating diversity. Life already exists for a very long time, so one of its characteristics must be diversity, because only then Life as such can survive extensive destructions of certain habitats as a result of major climatological and geological changes and catastrophes. The reason why some Hippoboscids have evolutionarily lost functional wings while others, living on the same type of host, have retained them, is just to retain diversity.
In the Implicate Order the noëtic reaction of the qualitative content of (1) Ornithomyia, of (2) Crataerina and Stenepteryx, and of (3) Myiophthiria and Brachypteromyia, with the qualitative content of the ecological niche offered by swallows, results in the respective (three) different states of the wings. And the very seat of these differences simply lies in the corresponding differences obtaining between the qualitative contents of the three mentioned groups of Hippoboscids. In this connection it is also clear that in contrast to a hippoboscid that has evolutionarily completely lost its wings, a hippoboscid still possessing vestigial wings can evolutionarily return to one with fully functional wings.

Crataerina  pallida  (Figure 3) is surprisingly common in the nests of the European swift, and may weaken or even kill nestlings by its voracious appetite for blood. Pupae overwinter in the deserted nest, and the new generation of adult flies emerges after the birds have returned in the following summer.  Crataerina  is thus obviously adapted to birds that return to the same nest, or at least to the same colony. If the nest is not reoccupied the hungry flies crawl -- being unable to fly -- in search of food.
All the Hippoboscidae of birds are likely to be taken on birds of prey, to which they have transferred when their original host was killed, so that hawks, owls, and falcons appear to be infested with a great variety of parasites.
The Hippoboscidae that live on mammals are the lesser section of the family, and apparently a later evolutionary experiment. Like the bird flies, they have their active, fully winged members, and their flightless ones. The genus  Hippobosca  itself consists of relatively large, handsome flies, with a striking pattern of brown and yellow, and with fully developed wings. They can be found on mules, horses, cattle, camels, and dogs. Other species of  Hippobosca  live on various antelopes and gazelles, and one species,  H. struthionis,  has transferred itself to the ostrich. This last example gives convincing support to the idea that it is the habitat that is significant to the fly, and not the specific nature of the host itself. Apparently to  Hippobosca  the ostrich is not a bird, a member of another zoological class of animals, but is simply a gazelle with feathers!
The active mammals of the steppes have active, fully winged Hippoboscids. The less active deer of woodland and open forest have their own group of flies, which have developed the curious habit of breaking off the wings, a habit also present in the bird-feeding acalyptrate  Carnus  hemapterus.  Adults of both sexes are fully winged for mating and finding a suitable host, but then they break off the wings near the base, and commit themselves to the fortunes of their host. They are able flyers, and it is not easy to imagine why they should have evolved the mechanism that is needed in order to shed the wings in this way. It is usually said that they benefit by being able to move freely about their host, unimpeded by the wings, but it is not obvious why  Lipoptena,  and the African  Echestypus,  should need this advantage, when  Hippobosca  is able to keep its wings.
There is something to be said for the complete loss of wings, as in the sheep ked,  Melophagus  ovinus.  Here the parasite has to live in a dense, tangled fleece, creeping about as if on the floor of a primeval forest.  Melophagus  has gone to the extreme of adaptation to this life, not only becoming wingless, but loosing the halteres too, and reducing the eyes further than any other Hippoboscid, see Figure 11 .  These wingless, flattened flies look like ticks, and are somtimes confused with the true sheep tick,  Ixodes  ricinus.  Their proper name is the sheep ked, and in a similar way  Lipoptena  cervi  is known as the deer ked, especially after it has shed its wings.
Hippoboscidae infest the kangaroos and wallabies of Australia, and the lemurs of Madagascar, mammals that are at opposite ends of their evolutionary line. The stage of evolution reached by the respective Hippoboscidae cannot be matched with that of their hosts, and once again it looks as if the flies spread into a habitat rather than on to a host, and made do with the mammals that happened to be there, regardless of their zoological classification.

Figure 5a :  Two common African louse-flies, parasitizing on birds.
Ornithoctona  laticornis  (upper image) possesses well-developed wings, while these are significantly reduced (in size) in  Crataerina  acutipennis  (bottom image), a parasite of the swift. 6 mm.
(After SKAIFE, LEDGER, and BANNISTER, in Afrikanische insekten, 1979)

[The evolutionary origin of Hippoboscidae can be described in about the same way as that of the Braulidae: The family of ancestral flies, not yet epizoic, successively occupies its intrinsically predetermined potential ecological niches. Many such niches do not significantly differ from the niche occupied by the evolutionarily first member of the family. And occupation of, and subsequent adaptation to, these niches, result in the addition of further metatypic characters to the family-groundplan core. That is to say, most of such characters are merely added to -- but without going to belong to -- the existing prototypical characters that constitute the family-groundplan, while only a few of them actually replace some prototypic characters. This means that the acquired adaptations and other adventive structures do not destroy the original family-groundplan. However, one or two species of the ancestral family can discover yet another potential ecological niche, namely to be epizoic on warm-blooded animals (Also here the discovery of this niche is being introduced by more or less regular interactions with these animals). And via injection, noëtic reaction, and projection we see new species appear which are fully adapted to this new way of life. But this time the adaptation is so far-reaching that almost all original family-prototypic characters have been replaced by these adaptive structures, resulting in the appearance of a new family-groundplan as we see it in the Hippoboscidae. But in contrast to the Braulidae, in the Hippoboscidae the order-groundplan (the groundplan "Diptera") generally remains explicit.]


In contrast to the Nycteribiidae (considered later), most of the Streblidae can be recognized as flies, though the females of  Ascodipteron  make up for this by looking quite unlike insects at all (see Figure 8 below).
Instead of being flattened like the Hippoboscidae, most Streblidae of the Old World have a cylindrical body, the thorax being nearly globular. Many of the Streblidae of the New World are more flattened, and  Nycterophila  coxata  could be mistaken for a flea. The tips of the tarsi (feet) are flattened, with powerful claws, and the whole body is covered with a neat array of bristles.

Figure 6 :  Pseudostrebla  ribeiroi  from Brazil.
(After JOBLING, from WEBER, 1966)

Most Old World Streblids have wings, and fly well on occasion, and their wing-venation is not widely different from that of other flies. They solve the problem of what to do with their wings by folding them in pleats along the back, in a way that is very convenient for them as they move about the fur of their host bats.

Figure 7 :  Wing of  Pseudostrebla  ribeiroi  (Streblidae). Length 2 mm.
(After JOBLING, from ROHDENDORF, 1951)

Streblidae are found only on bats, and then only in warm countries. JOBLING showed that their distribution falls neatly within the winter isotherm of +100C in the Northern and Southern Hemispheres, this being the critical temperature at which the bats begin to hibernate. During hibernation the body-temperature of the bats falls to within a fraction of a degree of that of their surroundings, and this is too much for the Streblidae :  In the few instances where they have occurred outside the mentioned limits there have been special circumstances, an exceptional year, or the protection of a cave against low temperatures.
JOBLING also notes that the Streblidae of the Oriental and Austral-asian regions are isolated from those of Africa and the Mediterranean. He attributes this to the low winter temperatures of the Iranian Plateau, where the bats are forced into hibernation, an invisible barrier that is none the less effective.
There are almost a hundred species known, in about twenty genera, and there is a sharp difference between those of the Old World and the New. While the number of species in the two hemispheres is about the same, the Old World has only four genera, while the New world has sixteen. Moreover there are differences between these two groups which suggest that they are descended from two distinct ancestral lines which diverged a long time ago. Since the American Streblidae have evolved so many genera of such diversified shape, they must have progressed more rapidly at first, whereas the Streblidae of the Old World are still at the species stage.
The relationships of Streblidae with their hosts, like those of Hippoboscidae with theirs, seem to depend more on the habits of the bats than upon their zoological relationships. Streblids are most abundant on bats that roost in caves, congregating in masses, often of more than one species of bat, and sharing their parasites as well as their shelter. When a species of Streblid is known only from one species of bat it is generally a bat that roosts in isolation, or with only members of its own species. Fruit-eating, forest-dwelling bats live more isolated lives than cave-bats, and tend to have their specific parasites, though sometimes they share these with cave-bats which make excursions into the forest and may even roost there sometimes.
The most remarkable Streblid, and one of the weirdest of all flies, is the genus  Ascodipteron, see next Figure.

Figure 8 :  Bat-parasites of the family Streblidae.
Adult females of  Ascodipteron  jonesi  embedded in the skin of a bat's wing.
(After OLDROYD, 1964)

The female fly not only remains on its host, but burrows into it with enlarged mouthparts until the parasite almost disappears from sight. Wings and legs are shed, and the sclerotized body is reduced to an almost unrecognizable remnant. On the other hand, the first abdominal segment swells and becomes a membranous bag, which envelops the rest of the fly, and converts it into a flask-shaped object from which the scientific name is derived. The male flies remain normal in appearance, and fly actively.  Ascodipteron  drops its larva to the ground where it pupates, in the same way as the larvae of Hippoboscidae and of tsetse-flies. All other female Streblidae attach their mature larvae to a wall or other surface, and this becomes encrusted with puparia from which the adult flies emerge in due course. Since they are already in the roosting place of the bats they have no difficulty in finding a fresh host.
Jobling considers that Streblidae probably arose from some ancestral muscoid fly that bred in the dung of bats in caves, but I [Oldroyd] am not sure that I agree. It is difficult to see why they should abandon a larval feeding medium that is at once organically rich and unlimited in amount.  Mormotomyia  has not done so [The larvae of this fly feed in the dung of the bats, and the adults appear to suck sweat and other body-secretions from the bats themselves. The family Mormotomyiidae is considered to be intermediate in evolution between the acalyptrate families and the dung-flies or Cordyluridae (Scatophagidae), which begin the series of calyptrates.], but lives all its life in the dung, not bothering about the bats themselves. I should have thought it more likely that the ancestral flies first developed the blood-sucking habit, like tsetse, and dropped their larvae to the ground in the same way, and as  Ascodipteron  still does. As the family flourished best on bats that lived a communal life in caves, the flies gradually came to deposit their larvae in the cave too, and so transferred their whole life into the roosting-place of their hosts.

[As regards the origin of the Streblidae in terms of one or more species of the ancestral not yet epizoic family discovering another potential ecological niche, of injection, of noëtic reaction, and of projection, we can say the same as we did with respect to the Hippoboscidae. Here the evolutionary sequence leading to Streblidae might be along the lines just suggested by Oldroyd : non-blood-sucking flies ==> flies sucking blood on bats and laying eggs in the dung of bats ==> flies sucking blood on cave-dwelling bats and laying fully-grown larvae in the cave.]


A similar origin perhaps may be postulated for the Nycteribiidae, also restricted to bats. The fact that these two families share the same hosts only serves to emphasize the striking differences between Streblidae and Nycteribiidae.

Figure 9 :  A wingless bat-parasite of the family Nycteribiidae.
Note the long legs, the small head (H), placed dorsally, and the hooked claws.
(After OLDROYD, 1964)

Nycteribiidae never have wings, and have evidently been without them for a very long time, because the thorax has lost its usual box-like structure as the flight-muscles dwindled. Streblidae still look like flies (except for Ascodipteron), but Nycteribiidae look like six-legged spiders. The upper surface of the thorax is little more than a framework of hard chitin, joined together with large areas of soft membrane, and the head is a grotesque structure apparently sitting on top of the thorax (See Figure above). Indeed, any one seeing a Nycteribiid for the first time is likely to mistake the under surface for the upper, and fail to find the head at all !  The eyes are greatly reduced, and may be absent altogether. When they are present they are quite unlike those of other adult flies, being either a single, round facet, or two little lenses on a black mount.
The female flies leave their hosts and attach their larvae to surrounding surfaces, the rock walls of caves, or trees where the bats roost, or to the timbers of roof-spaces in buildings. Some have been reported to attach their larvae to the hairs of the host bat, but this is not the general rule. Apart from this brief excursion, Nycteribiidae never leave their host except to move over to another bat with which it is in contact.
As in the other two families of Pupipara, host selection is not very precise, and seems to be more of a habitat-preference than a definite choice of a breeding host. As with Streblidae, Nycteribiidae that live on small bats congregating in caves are found to occur on a wider range of different species of bat than those living on relatively solitary hosts, such as fruit bats. The genus  Cyclopodia  favors the great flying foxes (Pteropus) while  Eucampsipoda  hyrtlei  and some other  Cyclopodia  infest the allied fruit bats of the genus  Rousettus.  The Nycteribiidae do not appear to harm the bats and are not known to carry any disease.
[End of abstract on Pupipara based on OLDROYD]

In the Nycteribiidae so many family-prototypic characters have been overwritten (replaced) by new adaptive structures that the original family-groundplan has become highly implicit or even totally deleted, resulting in the appearance of a new family-groundplan, that of the Nycteribiidae. Even many order-prototypic characters have been overwritten, resulting in the destruction of the basic 'fly-look'. See also next Figure.

Figure 9a :  Penicillidia  jenynsi  (Nycteribiidae),  from Formosa (Taiwan). Dorsal view of male (left), and ventral view of thorax and abdomen (right).
(After RICHARDS & DAVIES, in Imms' General Textbook of Entomology, 1977)

We said  "... have been overwritten (replaced) by new   a d a p t i v e  structures".  But when we compare things with the other representatives of the Pupipara (Hippoboscidae and Streblidae) we run into the problem of deciding whether a given structure is adaptive or not.  Let's go into this matter :
Streblidae and Nycteribiidae both live exclusively on bats and suck their blood. Frequently, a single species of Nycteribiid may utilize several species of host which may be of different genera or, more rarely, of different families. Conversely, a species of bat may support several species of Nycteribiids :  thus, at least 9 species of the latter have been recorded from  Miniopterus  schreibersi  in various countries. Because host selection in Nycteribiidae and Streblidae seems to depend more on the nature of the habitat where the bats live than on the precise species of bat, we can say that the respective ranges of hosts of the Streblids and Nycteribiids are expected to broadly overlap, so that we can affirm that they in fact live in the same ecological niche  [Of course there must be some difference in ecological niche, and we expect that to be of a biochemical or physiological nature, together with some other subtle differences in their relationship with the bats. Further, the mentioned overlap in host range of the two families does not necessarily mean that representatives of both families can be found to live together on a single bat individual (and, although I am not a specialist, I have not seen anything reporting this form of coexistence)].  So Nycteribiids and Streblids live in the same ecological niche (or at least in highly similar such niches), and their adaptive structures are therefore expected to be the same or at least very similar (because also their respective ancestral families were -- as can be assumed -- not very different from each other). But this is not the case. Streblids (and also Hippoboscids) have well retained the order-groundplan, they possess the 'fly look' (including the female of the Streblid  Ascodipteron,  mentioned above, because only before she makes a way beneath the skin of the bat near the base of the ear or sometimes elsewhere she casts both legs and wings). On the other hand, Nycteribiids never have wings and have, as it seems, lost almost all morphological characters that would determine them to belong to the order Diptera  ( They have, however, retained still relatively well developed halteres, while in  Melophagus  ovinus  (Hippoboscidae) they are completely absent, see Figure 11 ).  They look, as has been said, more like six-legged spiders. They are, apparently, highly adapted to an epizoic life on furred animals. But we cannot say that the Streblidae, being so different morphologically from Nycteribiidae, are less well adapted to such a life. And the same can be said of the Hippoboscidae (living not on bats, but on other mammals and on birds) :  Many of them possess wings and are definitively fly-like. For example  Ornithomyia,  see Figure 5 above , and  Hippobosca  depicted in the next Figure.

Figure 10 :    Hippobosca  rufipes.  From S.Africa.
(After RICHARDS & DAVIES, in Imms' General Textbook of Entomology, 1977)

And even where they do not possess wings and are not at all fly-like, as is the sheep ked  Melophagus  ovinus,  the result is not a spider-like appearance as in Nycteribiids, but a compact short-legged creature :

Figure 11 :  The sheep ked  Melophagus  ovinus.
(After RICHARDS & DAVIES, in Imms' General Textbook of Entomology, 1977)

Nevertheless we cannot assert that all these forms are in a lesser degree adapted than are the Nycteribiids. And the differences of body-habit between the winged Hippoboscids on the one hand and the Nycteribiids on the other cannot be attributed to differences in the groundplans of the respective ancestral families (giving rise to respectively Hippoboscids and Nycteribiids) because already within the Hippoboscidae we see both the fly-like and the non-fly-like body-habits. Also in Streblids we encounter both body-habits. And the three epizoic dipterous families (Hippoboscidae, Streblidae, Nycteribiidae) apparently come from comparable not too different cyclorraphic ancestral families, whose (small) differences cannot be responsible for the great morphological differences which separate these three epizoic families. We wonder therefore whether all the morphological structures in Nycteribiidae are really adaptive structures.
As we have explained, we assume that the evolutionary transformational process leading from the ancestral families to the respective epizoic diptera is the physical expression (as seen in the Explicate Order) of noëtic reactions occurring in the Implicate Order and the projection of their products into the Explicate Order. In the latter Order we apparently see this as evolutionary processes (in space and time) in virtue of which adaptive structures appear, giving rise to new families. Of course such evolutionary processes are not actually observed by us because if they actually do take place they take too much time. And in the present cases no relevant fossils are known. The evolutionary processes are therefore merely scientifically assumed to have taken place, assumed on the basis of available indirect data.
Because of the significant morphological differences obtaining between epizoic families that have essentially an identical way of life and are equally well adapted to it, we are forced to assume that the noëtic reactions, responsible for the origin of these families, are partly neutral with respect to adaptation, meaning that many of the new morphological characters that appear in virtue of them are not strictly adaptive, while others are. We could say that the several types of existing epizoic flies (fully winged forms, forms with vestigial wings, forms with no wings at all, and among the latter spider-like long-legged forms and forms with relatively short legs lacking a spider-like body-habit) are not representing different degrees of adaptation to a (blood-sucking) life among feathers or in fur, but are just different 'models' or versions of such an adaptation, expressing the omnipresent tendency of Life to increase diversity. So the nature of the difference between these versions is not adaptive, that is, the differences have not come about by ecological factors, they do not express different ecological types, but express purely  formal  types in the sense of structural groundplans.

*  *  *

In the present document we have discussed the way of life and the overall morphology of true epizoic diptera. We did this because they are significant for a theory of organic groundplans.
In the next document we will continue the development of the theory of groundplans and discuss in what way two totally different (larval) groundplans of predatory insects are nevertheless perfectly suited to fit into the same (larval) ecological niche. The mentioned groundplans are of predatory larvae of insects which are not taxonomically related :  They even belong to different insect orders, viz., Planipennia (Neuroptera) and Diptera.

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