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Oribatida mites: Fast runners and slow crawlers

Microhabitats often consist of a complexity of organism species. Under suitable conditions, samples can be kept „alive“ for months and even for years by regularly adding moisture and organic tissue, in case of my sample of this footage: patato pieces.



Mites of the Oribatida and their different ways of locomotion. Copyrights: Stefan F. Wirth, Berlin April 2019. Please give the video a like on youtube too.


Soil samples from island Norderney


This soil sample was collected in summer 2018 on the North Sea island Usedom during my participation at the „Geo Tag der Natur“. It contained several specimens of the predatory chilopode Lithobius sp. and pieces of rotting wood, moss and forestground, everything collected under rotting treetrunks and tree branches. The samples additionally contained the carabid beetle Pterosticus cf. niger and ants of genus Lasius. Samples were collected in a small forest area with wetland aspects. The soil quality was rather moist.


Astigmatid mites


I later added potato pieces and regularly some water droplets to the sample with still living big arthropods/ insects. After some weeks, specimens of the astigmatid mite Acodyledon cf. schmitzi developed on dryer areas of the potato pieces. These mites were presumably phoretic associates of the carabid beetles. They died out after several months, after the sample had dried out a little bit and may be due to changes of the room temperature during winter time.




Now, almost a year later, the micro habitat is inhabited by mites of the Oribatida in greater numbers of specimens of at least three species: Nothrus sp. (genus not yet clarified), Nothrus palustris (already found for the first time shortly after the sample collection) and a species of Phthiracarida.


Locomotion and biodiversity


Purpose of the short film is to show different organisms, cultured after about a year in this sample: mites, nematodes, collembolans and microorganisms, fungae and bacteria. Of the bigger arthropods/insects, only one Lithobius species survived until now.  Also the diversity of ways of locomotion in different oribatid species is emphasized: There are slow crawlers (Nothrus) and fast runners (Phthiracarida).


Berlin, April 2019, Copyrights Stefan F. Wirth

Mite Histiostoma sachsi (Astigmata): Juvenile dispersal instar deutonymph and its orientation behavior

Some animals live in environments, where there is (almost) no light available. It makes no sense to see in the dark, but it is important for a specimen to know, where it actually is, where it is going to, whether there is enough food and what the conspecifics are doing. Predators need to be recognized in time, and a sexual partner must be found. There is also need for an efficient communication between specimens of a species. How can all this be performed by mites of the Astigmata, which usually live inside decomposing soil habitats in a more or less permanent darkness?


Olfactory sense organs in mites of the Histiostomatidae


Histiostoma sachsi (Histiostomatidae, Astigmata) is such a mite, living inside cow dung or compost. It might have a rudimentary ability for a light perception, but has not visible or functional eyes. It cannot produce any sounds. It can only feel and smell. Seemingly very limited abilities, but the contrary is fact: Due to evolution this mite is perfectly adapted to its life-style. It can feel objects by touching on them using its body setation (= body hairs). And it smells by means of very specialized body hairs, which are called solenidia and appear in different types, shapes and functions. These mites don’t smell on the level of us humans, which would be very insufficient. If at all, it should be compared with a dog. I am always fascinated when seeing blind dogs and how perfectly they can interact with their environment, despite their handicap. That’s may be how the efficiency of olfactory perception abilities of such a mite must be imagined. They do not only perceive scent particles from other animals, plants and soil components. Even olfactory signals from their conspecifics will be correctly and differentiatedly interpreted. And that not only marginally.  Olfactory signals represent indeed the major mode of their intraspecific communication.


Chemical communication of mites of the Histiostomatidae


Communication always requires contributions from both sides, a signal and an answer. These mites smell the signal of a conspecific using their solenidia, and they answer by the secretion of biochemical components. For these purposes, they possess a huge and complex gland system located on the upperside of their backs. Volatile excretions aggregate inside a big and rounded reservoir and finally leak to the outside via a pore, called oilgland opening. These gland systems are located symmetrically on both sides, each with one reservoir and one pore.

The meaning of the sent volatile message simply depends on the composition of the correspondingbiochemical components. Even diffferent stereochemical configurations of the same molecule can have different meanings. Citral for instance is a major component and has in different stereoisomers different functions. Such cummunicative volatile signals are usually named pheromones. And mites of the Histiostomatidae can indeed produce different kinds of pheromnes via the same gland system. Aggregation pheromones inform specimens about a suitable place to stay together with their conspecifics, for example due to a sufficient amount of food resources. Alarm pheromones solicit mites nearby to flee from an unpleasant situation. Sexual pheromones attract adult partners to each other in order to perform the mating procedure. But the gland secretions can even more. As allomones, they communicate with specimens of other species. They function as defenses against predators or other dangerous cohabitants.


Deutonymphs need to find a carrier for dispersal


Another form of communicative interspecific interactions is performed by a specific juvenile instar, the deutonymph. It looks morphologically quite different from all other instars (heteromorphic situation), does not need or possess a functional mouth, has a thicker cuticle as protection against drying out and a complex sucker organ on its underside in order to attach itself to an insect or another bigger arthropod. Deutonymphs of the astigmatid mites search for bigger carrier-arthropods to get carried from one habitat to another (dispersal strategy  is calledphoresy). While doing so, they again use their specifically modified leg setation (hairs) on the first pairs of legs to perceive scents for the detection of a suitable and passing by carrier. Basically it is still unknown, whether the term „communication“ is indeed appropriate in this context as we don’t know yet about a mutual interaction between deutonymphs and their carriers, before the phoretic ride begins.



Olfactory orientation of the deutonymph of Histiostoma sachsi, copyrights Stefan F. Wirth, February 2019.


Specific way of walking in deutonymphs


In detail, different kinds of behaviors can be observed in deutonymphs, when searching a carrier. The detailed behavioral patterns in this context can slightly differ between even closer related species. Deutonymphs of Histiostoma sachsi as all deutonymphs show a characteristic mode of walking, in which especially the first pair of legs plays an important role. During each step, performed by four pairs of legs, the first legs are lifted up much higher than all other hind legs. While doing so, they slightly tremble up and down. A behavior that mostly supports a better basic orientation inside a „jungle-„micro-landscape, being filled up with soil particles and decomposing plant tissues. But what H. sachsi deutonymphs additionally need in order to find their carriers is repeatedly to rest between the walking activities. Thus the first legs, which normally are still walking legs, are made free and that way available for the perception of carrier-scent-components only. These  namely are the legs that bear the highest densiy of solenidia.


Two different behavioral modes for an efficient orientation towards a carrier


Two different modes of resting with olfactory searching activities could be observed: In periodic intervals the deutonymph attached to the ground by using its sucking structures. They were then more or less laying on their entire undersides with only their forebodies slightly lifted up. By alternating moving the first legs up and down, olfactory information could be perceived from all directions without having the own body as a barrier to backwards. To improve its orientation situation, the deutonymph additionally turned on its own axis around, being stabilized by its sucking structures, which are flexible enough to follow these movements. When the deutonymph intended to continue its walk, it first needed to detach from the ground, which happened via muscle contractions that caused an abrupt detachment of the corresponding suckers. But main aim of the deutonymph is to find an elevated place, where the probability of a passing by carrier is especially high and from where a bigger insect (or other arthropod) can easier be ascended. There the second behavioral mode was performed. The deutonymph only fixed the edge of its hind body to the ground, again using the suckers on its underside, which are located close to this edge. This time the entire mite body stood in an upright position. The first legs again „waved“ alternating up and down and could under these especially elevated conditions even perceive scents from bigger distances. By occasionally slightly and alternating turning their upright bodies to both sides, olfactory information could be easier detected from all directions.


Carrier of H. sachsi still unknown


The frequency of such movements in mites increases typically as closer a suitable carrier approaches. But this was not yet observed or documented for Histiostoma sachsi. Its carrier inside the compost substrate is still unknown, which is why I so far could’t perform corresponding experiments. The species‘ describer, Scheucher (1957), found her mite specimens in cow dung and also didn’t identify the corresponding carriers there.

The observations presented in my video are part of my research project about morphologies and behaviors of deutonymphs in the Histiostomatidae.


Berlin, February 2019. All copyrights Stefan F. Wirth.


Eudicella colmanti – Mating behavior of a colorful beetle

Rose chafers represent a group of colorful beetles, which taxonomically belong to the Scarabaeidae and thus are relatives of famous beetles such as Scarabaeus sacer, well known for rolling dung into balls and for being an important symbol for creation and the rising sun in the ancient Egyptian world. Even the stag beetles are more distant relatives of rose chafers.


Colorful and active during daytime


Unlike some related beetle clades, rose chafers are usually active during the day. This is also indicated by their very colorful bodies. Colors in insects can have different functions, but they usually all are optical signals, which require a visibility in the sun light. Greenish colors are common in rose chafer species and might have optical inner specific signal functions, but also might support an optical camouflage. This would also make sense in the preferred habitats of the adult beetles, which usually feed on softer parts of blossoms and on their pollen. But they also feed on fruits, whereby mostly liquids are incorporated as the chewing mouthparts are not very well developed.


Tropical rose chafer Eudicella colmanti during its copulation behavior, 4K videography, copyrights Stefan F. Wirth.


Tropical rose chafers from African countries


About 3000 species of rose chafers are known, of which most inhabit the tropical zones. The about 20 species of the genus Eudicella are more or less restricted to the African continent.

Eudicella colmanti is native to Gabun, Kamerun and Kongo, thus a species with a main distribution in Central Africa. But E. colmanti is like other species of this genus worldwide often kept in terraria, although species like E. smithi are more common inhabitants of this kind of artificial habitats. They all can be more or less easily reared.


Specific flying mode and copulation behavior


This is why I was able to study behavioral characters in detail. And rose chafers indeed show interesting behaviors. They for example perform a unique way of flying. It is a specific character of rose chafers (a so called apomorphy) that they fly with closed fore wings, which cannot be opened as in other beetles.

I documented in my video the mating behavior of a beetle couple. Interestingly this was not too difficult, although both genders can, when separated from each other, react to disturbances with a high agility.


Almost permanent copulation activities


But in the copulatory position, they accepted to be removed from their terrarium to the filming set and even stayed in position, when they were enlighted from different positions with very bright light beams. Please note the the female, which I observed regularly actively searching for a position underneath the male (behavior not clearly visible in my footage). But it also conspicuously never stopped feeding (on an apple) during the copulatory process (very well visible in my footage), obviously to obtain enough nutrients for the production of eggs. A copulation in my couple is not a unique event, but is repeated regularly and can take hours.


Phoretic mites


Both genders carried bigger numbers of mites. These were phoretic deutonymphs of the taxon Astigmata (Acariformes, Acaridae). As never determined the mite species, as it was not clear, whether it represented a natural associate of these tropical beetles, or whether it was a species native to Germany, which for example was carried into the terrarium via Drosophila flies.

Copyrights Stefan F. Wirth, Berlin March 2017/ February 2019

Berlin forest Grunewald – former gravelpit area, type location for the mite Histiostoma palustre

The city of Berlin geomorphologically consists of witnesses of the Weichselian glacier. The modern city itself and adjacent federal states represented end moraine areas with fluvio-glacial debris accumulations,  even well visible today due to a very sandy soil composition and a corresponding vegetation, creating landscapes, which partly almost look like from around the Mediterranean Sea.

Sands carried by the glaciers towards their end positions remained in partly huge layers with a thickness of up to 20 meters or more.


Gravelpit zone and its history


Also the area of the old gravelpit zone, called „Sandgrube im Jagen 86“, in the Berlin forest Grunewald is located inside such an end moraine zone, which was represented by plates belonging to the geological Teltow-plateau. In the time period between 1966 and 1983, gravel was excavated for industrial purposes. After 1983 a part renaturation was supported by nature conservationists. In 1992 in total 13 hectares of the former gravelpit area were allocated as nature conservation areas.

Other parts of this unique landscape remained accessible for the public. They represent today popular places for leisure and experiences of nature. Especially the huge sand dune is a popular destination for families with children.


Aerial videography of the gravelpit area in January 2019, copyrights Stefan F. Wirth. Please like my video also on Youtube, in case you like it.



Gravelpit zone and its ecology and biodiversity


The whole area – nature protection and accessible zones – show a complex mosaic of different  landscape types, offering numerous animal and plant species a well suitable refuge.  Neglected grasslands and dry meadows are surrounded by sandy areas free of any vegetation („dunes“) and moist osier beds and wetlands with ponds. The wetlands represent breeding grounds for numerous amphids. Lizards such as the sand lizard Lacerta agilis and snakes such as the grass snake Natrix natrix can regularly be observed. Sandy habitats offer space and specific ecological conditions for a interstitial fauna, consisting for example of different bee and sand wasp species.

In total the area bears more than 300 ferns and flowering plants, 16 breeding bird species, 7 amphibian species and 188 butterfly species.


My own scientific mite research in the gravelpit area


I was performing scientific research in that gravel pit landscape during the work on my phd-thesis between 2000 and 2005. My interest was (and one of my interests is still) focussed on specific organisms living around the shoreline of ponds.

The whole area of the gravelpit landscape is a good example for ecological changes that happen naturally with the ongoing time or even being affected by climatic changes. Between 2005 and 2018, the landscape partly changed significantly. Neglected grasslands and dry meadows covered less space originally, and instead several smaller ponds existed and offered amphibs and wetland inhabiting insects additional habitats. But some of the ponds already years ago dried out permanently. Their remnants are now covered by extended dry grasslands.

In former times of my phd thesis and even today, my research interests focus and focussed on the mite fauna in and around the muddy shorelines of ponds inside this former gravelpit area. The ponds are mostly surrounded by sapropel, a seemingly black and brownish mud, which is colored that way due to the incorporation metal sulfides. These muddy areas develop due to biochemical modifications of organic material in the absence of oxygen. Different insects, especially beetles live on top of these waterside habitats or even inside. Carabids of genera Elaphrus or Bembidion represent predators, while heterocerid beetles of genus Heterocerus are substrate feeders, presumanly with a preference for diatoms. Also water beetles of Dytiscidae and Hydrophilidae inhabit these habitats.


The mites Histiostoma maritimum and Histiostoma palustre


I discovered some of these beetles as dispersal carriers for specific mites. The dispersal strategy to take a ride on bigger animals to become carried from one habitat to another is called phoresy. Mites of the Astigmata represent typical phoretic organisms. I am scientifically specialized in a specific family of the Astigmata, which is named Histiostomatidae, and I discovered the mite species Histiostoma maritimum Oudemans, 1914 on Heterocerus fenestratus and H. fusculus as well as on Bembidion and Elaphrus species insside and on top of these muddy zones. I was the first acarologist, who ever studied the biology of this mite species. I furthermore discovered another mite species that was completely new to the scientific knowledge, and thus I scientifically described it as Histiostoma palustre („palustris“ = „muddy“) in 2002.

This species deserves particularly mention due to an unusual biological phenomenon: populations show a so called male dimorphism (better diphenism). Besides males with a „normal“ morphology, morphologically modified males appear. Their second legs differ from the typical shape of a mite and are modified into clasping organs. The function of these conspicuous organs could so far only be interpreted in the context of male to male competition conflicts for a female. In such situations, I observed the organs being used as arms against other males, against such ones with and such ones without clasping organs.



Right modified leg of a male of Histiostoma palustre. Copyrights Stefan F. Wirth, 2002/ 2019



Modified leg of a H. palustre male in closed position. Copyrights Stefan F. Wirth, Berlin 2002/ 2019



Underside of a H. palustre male with modified leg. Copyrights Stefan F. Wirth 2002/ 2019



Asymmetry: male of H. palustre with only the right leg modified. Copyrights Stefan F. Wirth 2002/ 2019


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Asymmetry: male of H. palustre with only the left leg modified. Copyrights Stefan F. Wirth 2002/ 2019



Copulation of a Histiostoma palustre male with both-sided modified legs. Copyrights Stefan F. Wirth, Berlin 2002/ 2019



Details of a copulation with a modified male, copyrights Stefan F. Wirth, 2002/2019



Berlin, January 2019. Copyrights Stefan F. Wirth

Phoretic Mites waiting on Ant Pupae

Greater numbers of pupae from a nest of the myrmecine ant Myrmica rudinodis are attached by phoretic mites, which wait for these pupae to hatch. They would then attach the newly developed ants to be carried around and dispersed this way. They this way had already occupied their later ants before, namely during their pupal stage, one could call this phenomen „pupa-guarding“. In my samples, I discovered two species of mites performing this pupa guarding behavior. Most abundant were deutonymphs of the mite Forcellinia wasmanni (Astigmata). But also individuals of a mite species of the Gamasina were repeatedly discovered sitting on pupae, where they were hiding between head, ventrum and limbs of the pupa. They even seemed to defend their pupae, when they felt disturbed, e.g. by my filming activities.


Ant pupa guarding by mitees, looking for a carrier for dispersal


These pupa guarding-findings concerning this ant and with these corresponding mite species might be new to science (so far I didn’t found literature indications) and thus need to be studied closer in the future in order to understand the whole context of behaviors. In the footage, two types of pupae are visible, pupae of the winged alates and those of workers. Mites generally prefered both, but especially the deutonymphs of Forcellinia wasmanni seemed to appear more often on the pupae of later workers. Most pupae had at least one deutonymph attached, rarely, there were found up to four individuals. This is different to what could be found on older workers. They on their ventral side can have 4-6 deutonymphs. Many workers seem to be covered with the deutonymphs, but I didn’t check more workers until now, so I can’t say, how many were without mites. It is unknown, how deutonymphs come to the pupae, whether they simply leave older workers for the pupa-guarding or whether they were waiting in the soil for the pupae to arrive (due to the brood caring activitoes of the ants).

Mite-Life inside an ant nest. Copyrights Stefan F. Wirth 2015/18


Astigmatid mite with a strict relationship to ants


The mite Forcellinia wasmanni is known to be strictly associated with ants (e.g. Türk & Türk 1957). It is clear that attaching young female alates would secure the dispersial of the mite into a new ant nest. It is not clear, which function the transport via ant workers can have. But Türk & Türk (1957) mention that the free living instars of Forcellinia wasmanni would feed on dead ants. Such a kind of microhabitat for the development is not unique in astigmatid mites. Some species within the Astigmata are known to have such preferences for decaying cadavers, but are then feeding on microorganisms, which grow on these (insect) cadavers. Ant workers might be ideal to carry mite deutonymphs to new cadavers, where they would leave and develop. Ants generally have a very well developed hygienic behavior. This guarantees the mites to get access to cadavers regularly. I do not know any other video footage, showing living deutonymphs attached to their carriers on such a magnification level as visible in this film. The original footage of these deutonymphs is much longer.


Morphology and behavior of the dislersal-instar, the so called „deutonymph“


The function of the proterosoma (dorsal shield of the forebody) is acting as a flexible structure, protecting the mouthpart-area (non-functional in deutonymphs) and the fore-legs, but being very motile and being easily pushed backwards (under the following hyterosoma-shield), when the mite lifts up from the surface of the ant pupa. I cannot state much more concerning the second mite, found on pupae, which is a species of the Gamasina. I discovered this phenomenon only on three of my pupae. Ant nests represent complex communities of organisms, to which fungae, other insects, mites and nematodes can belong. The samples visible in this film were collected in July 2015 on the German island Usedom inside a forest area between the villages Zinnowitz and Karlshagen. The ant nest was quite small. An ant hill was not visible.


Complexity of life in ant nests


The complexity of life within ant nests is a result of evolution. I am an enemy of creationistic movements, including all modern faces of creationism. Creationism stimulates carelessness und illiteracy in the believing people.



Berlin August 2015/ December 2018, copyrights Stefan F. Wirth

Habitat compost: Mite Histiostoma sachsi carries old cuticle and dirt as camouflage

My parents have a compost area in their backyards. I use it as reference habitat for two mite species of the family Histiostomatidae (Astigmata): Since I began my research in 2000, the compost regularly contained Histiostoma feroniarum with its typical male dimorphism. Since summer 2017 another species appears additionally regularly: Histiostoma sachsi. Both species do not appear under the same conditions. While H. feroniarum prefers fresher decaying material, H. sachsi on visibly older decomposed tissue. There mite be even more mites of the Histiostomatidae exist in this complex compost habitat, but under my laboratory conditions, only the two named species were so far successfully reared out of samles always again. Regarding the determination of H. sachsi on a species level, I was more careful in my comments to a former video (June 17), in which I named it Histiostoma cf. sachsi due to doubts about a correct identification. Meanwhile, also due to the morphology of the deutonymph, I determine „my“ compost mite as Histiostoma sachsi Scheucher, 1957. But it is still to emphasize that Scheucher described H. sachsi from cattle dung, not from compost. But generally, both habitats can sometimes share the same inhabitants.


Adult females carry their old cuticles and „dirt“ on their backs as tactile comouflage


Biologically conspicuous is darkish material, which especially adult females carry on their backs. Unlike males, females posses elongated setae on their backsides. These setae support the holding of material such as old cuticle and soil particles. In slide preparations, this cover usually appears amorphic and contains substrate from the mite’s environment. My video footage indicates that the basis of this cover is a retained old cuticle from the former nymphal instar . That this cannot easily be proven with the light microscope is due to the very soft and fine character of the cuticles in these mites. Remnants might become decomposed by microorganisms after a while.

Compost: the habitat of the mite Histiostoma sachsi Scheucher, 1957 (Acariformes, Astigmata, Histiostomatidae). Copyrights Stefan F. Wirth, please like my video also on youtube, in case you like it.


The phoretic dispersal instar, named deutonymph, in mites of the Astigmata controls its body position due to sticky leg endings and suckers on their undersides


Deutonymphs of H. sachsi represent one of my resent models to study mite-dispersal behavior. My research focus since a while concerns ultrastructure and function morphology of the deutonympal suckerplates and other structures to attach to insects for dispersal (this dispersal strategy is called phoresie). The anterior front-suckers on the suckerplate of the mite’s underside is extendable and very flexible, not only to find a suitable position on the insect carrier. When falling, the deutonymphs use it to lift their bodies up into a proper position again. Additionally they will try to get hold using „sticky“ lobe-shaped setae on the endings of legs I and II. Both is visible in my footage. The forelegs seem generally to make the first contact, when trying to get on a suitable carrier.


Deutonymphs of Histiostoma sachsi take a ride on other mites (Oribatida)


The suitable carrier of H. sachsi is unknown to me. Some astigmatid species have even a range of carrier-„hosts“. In my samples, deutonymphs at least attach to other mites, especially to mites of the Oribatida. This is in a very short scene visible in my video too.


Copyrights Stefan F. Wirth, Berlin December 2018

A scarab beetle’s larva and pupa: habitats for mites and other organisms

The micro-world is complex. Its habitats intertwine themselves, some even are unusual, because they are formed by single animal individuals. An example is a holometabolic insect, here the tropical rose chafer Eudicella colmanti. The larvae of my specimens are covered with deutonymphs of an astigmatid mite (Acaridae, eventually Acarus sp.).

This makes the beetle larva to a habitat for these mites, although the mites in this case don’t feed or reproduce there. They instead are „only“ passengers on their transportation to a new „real“ habitat, where they become adult, feed and reproduce. This strategy to be carried by other organisms from one living place to another is called phoresy.

The situation in my terrarium might be artificial in the sense that mites are putatively not of tropical origin as the beetles (reared in Germany) and thus do not originally „belong“ to the beetle species. The mites might have reached into the terrarium via fruit flies or similar native organisms or via the terraria of the online shop, where they were bought. But the mite deutonymphs show a distinct affinity for adult beetles and their larvae nevertheless, which they attached in great numbers (not the pupa). The microscopic footage of the mite deutonymphs contains activities of their genital openings, located close to the sucker plates on their undersides.

They occasionally open and close and discharge secretions or water. This might be due to osmoregulation and/or in order to prove the adjacent sucking structure with moisture for a more stable hold.

The larva after some months built its pupa chamber, consisting of soil particles and larva secretions. Tese pupa chambers offer on their outer sides obviously enough nutrients for collembolans, which appeared there in greater numbers, especially on an older chambers with its pupa waiting to hatch. Mites of the Gamasida and tiny annelids could also be observed there. The video consists of macro fotage and microscopic footage, all recorded in 4K and rendered in an uncompressed quality.


Berlin, December 2017/November 2018, copyrights Stefan F. Wirth

Das Geheimnis der Bernstein-Tierchen

Image    Stefan F. Wirth betreibt Forschung in den Bereichen Zoologie, Acarologie, Evolutionsbiologie und Ökologie in Kooperation mit verschiedenen internationalen Instituten. Sein Forschungsschwerpunkt sind Milben, die an Insekten und andere Arthropoden gebunden sind. Außerdem doziert er an der FU Berlin zur Biologie der Insekten und Milben sowie zu evolutionsbiologischen und ökologischen Themen. 

© aller Textpassagen Stefan F. Wirth. Alle Rechte der Textpassagen vorbehalten, insbesondere das Recht auf Vervielfältigung und Verbreitung sowie Übersetzung. Kein Teil dieser Seite darf in irgendeiner Form ohne schriftliche Genehmigung von Stefan F. Wirth reproduziert werden oder unter Verwendung elektronischer Systeme verarbeitet, vervielfältigt oder verbreitet werden. Die Weiterverwendung der Fotos erfortert zudem die Zustimmung weiterer Personen des Urheberrechts. 

Da ich mich von nun an selbst publizieren möchte, habe ich den Artikel, für den nur ich die Urheberrechte besitze, von der Seite entfernen lassen.


Bernsteine stammen aus längst vergangenen Zeitaltern. Manchmal sind in diesen Steinen winzige Tiere eingeschlossen, Milben oder kleinste Spinnen beispielsweise. Noch steht die Erforschung dieser Wesen am Anfang. Doch sie verspricht spannende Erkenntnisse über die Frühzeit des Lebens. Von Stefan F. Wirth .

Fast jeder kennt die orange-gelb schimmernden und häufig durchsichtigen Steine und hat womöglich schon Museums-Stücke bewundert, die manchmal im Innern winzige Tierchen beinhalten – wie im Foto links: eine Spinne. Bernstein ist ein ungemein ästhetisch anmutendes Gestein. Nicht umsonst gilt das legendäre Bernsteinzimmer des Preußenkönigs Friedrich I. als  „achtes Weltwunder“.

Bernstein ist dabei nur der Sammelbegriff für vorzeitliches Baumharz, das die Jahrmillionen überdauerte. Im Detail gibt es unterschiedliche Sorten aus verschiedenen Zeitaltern, die sich im chemischen Aufbau voneinander unterscheiden.

Doch welchen Nutzen hat Bernstein für die Forschung? Warum sind mikroskopisch kleine Milben darin zum Beispiel interessante Studienobjekte, und warum ist davon auszugehen, dass manche Tier- und Pflanzenarten, die gemeinsam im Bernstein eingeschlossen wurden, sich dort nicht zufällig begegnet sind, sondern vielmehr üblicherweise gemeinschaftlich auftreten?

Die Frage lässt sich zunächst allgemein beantworten: Fossilien, um die es sich ja auch im Falle der Bernstein-Organismen handelt, gewinnen häufig durch den Vergleich mit heutigen Lebewesen erst an wissenschaftlicher Aussagekraft.

Finden wir zunächst also scheinbar nichts weiter als eine Hummel, eine Ameise, einen Käfer oder eine Spinne im Bernstein erhalten, dann stellt sich bei genauem Hinsehen heraus, dass diese Tiere selten allein sind. Winzige Organismen sitzen auf ihnen drauf. Sind das natürliche Bedingungen oder Zufälle?

Blinde Passagiere, Mitflieger und Reisegesellschaften

An Fossilien kann man das manchmal nicht mit Sicherheit beantworten. Untersucht man jedoch noch heute lebende Gliedertiere, wird man feststellen, dass es tatsächlich „Mitreisende“ gibt. Und die kann man mitunter sogar leicht mit dem Transport-Tier zusammen züchten und die Zusammenhänge derartiger Bindungen zueinander im Detail studieren. Erst wenn solche Erkenntnisse aus der heutigen Welt der Tiere vorliegen, können Wissenschaftler Fossilien hinreichend verstehen und im richtigen Kontext interpretieren.

Tatsächlich zeigen Vergleiche mit heutigen Organismen, dass die oben genannten Tiere regelmäßig Mitläufer oder Mitflieger an sich tragen. Man kann sogar sagen: Das Insekt oder die Spinne wird zum Lebensraum, einem Mini-Ökosystem, obwohl manche dieser blinden Passagiere eher an ruhende Taxi-Passagiere erinnern und weniger an aktive Lebewesen.

Ökosysteme sind für Biologen interessante Forschungsobjekte. Darunter versteht man meist die Gemeinschaft verschiedener Arten, die in einer Wechselwirkung mit ihrer (unbelebten) Umwelt stehen. Manchmal finden sich sogar Hinweise auf eine gemeinsam verlaufene Evolutionsgeschichte der verschiedenen Organismen, die zu solch einer Artengemeinschaft gehören, zum Beispiel der auf einem Insekt. Das Phänomen, in dem nicht näher miteinander verwandte Organismen sich schrittweise durch Evolution aufeinander spezialisiert haben, bezeichnet man als Koevolution.

Man kennt solche Hinweise auf parallel verlaufene Evolutionen zum Beispiel von Blütenpflanzen und einigen sie bestäubenden Insekten. Wie man eine solche Koevolution überhaupt nachweisen kann?

Hierzu müssen die Evolutionsbiologen Stammbäume rekonstruieren und nachprüfen, ob die der betroffenen Organismen an entsprechenden Stellen ein ähnliches Verzweigungsmuster aufweisen.

Im Zusammenhang mit Insekten und anderen Gliedertieren sind parasitische „blinde Passagiere“ bekannt, die es häufig auf das Blut ihrer Wirte abgesehen haben. Aber auch solche „Mitreisenden“ kennt man, die nur transportiert werden wollen, weil sie zu klein und zu langsam sind, um neue Lebensräume selbstständig erreichen zu können. Manche der Parasiten und auch einige dieser neutralen „Mitreisenden“ haben offenbar einen langen Abschnitt ihrer Evolution in Wechselwirkung mit der ihres Insektes durchlaufen. In vielen anderen Fällen ist die Forschung noch immer gefordert, diese Zusammenhänge zu klären.

In Bernstein eingeschlossen: Farne, Moose, Flechten und kleine Wirbeltiere

In meiner Forschung sind besonders solche Milben dankbare Studienobjekte, die sich bei einer Größe von weniger als einem halben Millimeter mit komplizierten Saugnäpfen auf Insekten und anderen Tieren festheften, um so transportiert zu werden – (das unten stehende Foto zeigt die Milbe bei lichtmikroskopischer Vergrößerung).

Es handelt sich dabei nicht um Parasiten, sondern vielmehr um neutrale „Mitflieger“. Häufig werden nämlich fliegende Insekten von Milben als Transportmittel bevorzugt, denen im Übrigen trotz mitunter recht zahlreichen Passagieren kein bemerkbarer Schaden entsteht.

Derlei „Reisegesellschaften“ gab es bereits in längst vergangenen Zeitperioden unserer Erde. Sie sind bislang aber sehr unzureichend untersucht worden. Besonders ergiebig für die Milbensuche ist Baltischer Bernstein, der wissenschaftlich übrigens als „Succinit“ bezeichnet wird. Bernsteineinschlüsse werden der Forschung noch Überraschende Erkenntnisse liefern.

Doch was hat es mit diesem Gestein auf sich? Bernstein mit Einschlüssen konnte sich bilden, indem Organismen wie Moose, Farne, Flechten, kleine Wirbeltiere und insektenartige Gliedertiere zufällig in das noch flüssige Baumharz von Nadelbäumen gelangten, wo sie festklebten und vollständig umschlossen wurden. Nach dem Erhärten des Harzes, das die eingeschlossenen Organismen nun luftdicht eingebettet vor bakterieller Zersetzung bewahrte, sorgten chemische Veränderungen dafür, dass aus dem Baumharz-Brocken Schritt für Schritt Bernstein wurde, wie wir ihn heute kennen.

Was simpel klingt, konnte im Detail noch nicht durch die Wissenschaft erklärt werden. So ist zum Beispiel nichts über den Artenreichtum Succinit-bildender Bernstein-Baumarten bekannt. Stittig ist auch, welche Verwandten der Bernsteinbäume es unter den heutigen Nadelholz-Gruppen gibt.

Nicht mehr bezweifelt wird indes, dass die Bernstein-Bäume ungewöhnliche Eigenschaften hatte: Sie besaßen ein besonders schnell aushärtendes Harz, wie wir es bei modernen Nadelbäumen in dieser Ausprägung nicht finden können. Es gibt klare Hinweise, die belegen, dass es bereits am lebenden Baum zu seiner endgültigen Gestalt erstarrt sein muss. Nur so ist zu erklären, dass die tierischen und pflanzlichen Einschlüsse unversehrt in ihrer ursprünglichen Form erhalten bleiben konnten, ohne dass es durch den späteren Druck beim Einlagern in die Erde zu Verformungen kam. Deformationen kennen wir von Fossilien aus Schieferlagerstätten nur zu gut.

Baltische Bernsteine sind etwa 30 bis 50 Millionen Jahre alt und entstammen einer Region, bestehend aus der heutigen Ostsee und der skandinavischen Halbinsel, die einst mit ausgedehnten Wäldern bedeckt war.

Erforschung einer weitgehend unbekannten Mikrowelt

Obwohl Bernstein in unterschiedlicher chemischer Zusammensetzung und auch aus verschiedenen Zeitepochen erhalten ist, erweist sich der Baltische Bernstein als besonders zahlreich mit darin eingeschlossenen Organismen versehen. Dies ist jedoch vor allem auf seine Fundhäufigkeit und die damit einhergehende bessere wissenschaftliche Bearbeitung zurückzuführen.

Vertreter von Insekten, aber auch Asseln als Repräsentanten der Krebse, Hundertfüßer und Spinnentiere sind in all ihren mikroskopisch kleinen Strukturen so wunderbar erhalten, dass man glauben könnte, sie seien erst gestern verstorben.

Die Mikrowelt aus Milben und Insekten, Spinnen oder Tausendfüßern im Bernstein ist nur unzureichend erforscht und wenn überhaupt, dann nur lückenhaft dargestellt, was oft vor allem auf technische Beschränkungen zurückzuführen ist. Denn wie soll man eine Milbe aussagekräftig sichtbar machen, die weniger als einen halben Millimeter groß ist? Selbst hoch auflösende Lichtmikroskope sind überfordert, zumindest solange der Anspruch erhoben wird, den Bernstein nicht zu beschädigen. Denn dies wird häufig von den Museen oder Sammlungsbesitzern nicht gestattet.

In dieser Situation befand sich auch die Bernstein-Milbe, die ich zusammen mit einem Kollegen des Museums für Naturkunde in Berlin und weiteren Wissenschaftlern aus Manchester untersuchte. Das nur etwa 176 µm lange Tier, ein Jugendstadium, das als „Deutonymphe“ bezeichnet wird, sitzt festgesaugt auf dem Vorderkörper einer ausgestorbenen Sechsaugenspinne (eine bedrohlich aussehende Webspinnen-Gruppe, die auch heute noch vorkommt), bei der es sich um genauso ein Original handelt, das als Vorlage für die neue Beschreibung dieser Spinnenart diente. Daher durfte das Bernsteinstück nicht zerschnitten werden, um beispielsweise mikroskopisch dünne Schliffe für die Untersuchung mithilfe normaler Lichtmikroskope anzufertigen.

Um die winzige Milbe, die aus der recht großen Gruppe der so genannten „astigmaten Milben“ stammt, dennoch dreidimensional sichtbar machen zu können, entschlossen wir uns, die Computertomographie einzusetzen. Ein eventuell wegweisendes und ungewöhnliches Unterfangen!

Unserer Kenntnis nach haben wir in unserer Publikation aus dem Jahre 2011 weltweit erstmalig ein Tier dieser winzigen Größe (176 µm) mithilfe der einfachen Mikro-CT  dreidimensional und in sehr guter Auflösung darstellen können.

Wir wissen jetzt: Schon vor Millionen von Jahren gab es „Taxis“

Unser Erkenntnisgewinn: Es handelt sich scheinbar um den ältesten bekannten Nachweis einer Milbe aus der Familie der Histiostomatidae (wobei aufgrund der fossil erhaltenen Merkmalssituation – die Milbe war teilweise beschädigt – des Tieres auch die Zugehörigkeit zu einer anderen, nah verwandten Milben-Gruppe nicht  auszuschließen ist). Das Alter des Tieres aus dem Eozän (44 bis 49 Millionen Jahre) wird von uns als Mindestalter angesehen, dennoch wissen wir nun sicher, dass die eigenartige Verbreitungsweise dieser Milben, nämlich ein größeres und schnelleres Tier als „Taxi“ zu gebrauchen, schon Millionen Jahre alt ist.

Aus der Milben-Gruppe, mit der ich mich derzeit befasse, sind bislang nur wenige Fossilien bekannt, was auf die geringe Größe dieser besonders kleinen Tiere zurückzuführen ist. Sie werden dadurch nämlich oft übersehen. Bessere optische Technologien, aber auch die gewachsene Aufmerksamkeit der interessierten Zoologen, werden dazu führen, dass bislang im Bernstein kaum beachtete Vertreter winziger Tiere wie diesen Milben, künftig viel besser wissenschaftlich bewertet werden können.

Auch das aus evolutionsbiologischer Sicht äußerst spannende Phänomen der gemeinsamen, aneinander gebundenen Evolutionsgeschichte unterschiedlicher Tiergruppen kann durch Bernsteinfossilien künftig wohl besser verstanden werden.

Ein gutes Beispiel für diesen Forschungsansatz sind Milbenarten, die an unterschiedlichen Arten von Borkenkäfern gebunden sind. Möglicherweise hat man es hier mit Koevolution zu tun. So bearbeite ich derzeit ein Bernsteinstück, das einen heute ausgestorbenen Borkenkäfer mit winzigen Milben behaftet enthält. Diese Milbenart zeigt bereits äußerliche Merkmale, die man auch bei heutigen Borkenkäfermilben aus dieser Verwandtschaftsgruppe finden kann.

Es ist im Übrigen ganz grundsätzlich bei der Bewertung von Fossilien stets zu berücksichtigen, dass sie die Artenvielfalt und ökologische Zusammenhänge vergangener Zeitalter, abhängig von zufälligen Einbettungsereignissen, stets nur lückenhaft wiedergeben. Fossilien sind daher als kleines Puzzlestück aus einem großen Ganzen zu bewerten, das zu einem beträchtlichen Teil auf immer verloren ist.


Foto oben: Spinne im Bernstein – Copyright: Jason Dunlop, Museum für Naturkunde Berlin.

CT-Foto unten – Copyright: University of Manchester/Andrew McNeil.