Flies were caught on warm and dry days (20–30°C) close to a dog meadow, poultry house, cattle barn, horse stable, pigpen, and rabbit cages in the surroundings of the small town of Dormagen near Düsseldorf in Germany. To avoid contamination by the tissues of typical insect catchers, the flies were first caught either with sterile vessels or with commercial sterile plastic bags and were immediately placed for 5–10 min in sterile petri dishes on blood agar. After this incubation, the flies were removed from the petri dishes, killed by CO₂, and identified under a dissecting microscope. Later, larger numbers of flies were also caught with freshly washed butterfly nets. In these cases only the intestinal contents of these flies were examined.

The catching sites at four selected recreation sites (often with crowds of people and where there were also numerous birds—geese, swans, ducks, and pigeons) were situated in larger towns or close by them. The following four sites were selected:

The flies were caught at intervals of 7–14 days (depending on the weather) with the help of butterfly nets, the opening of which had a diameter of 25 cm. The flies were transferred singly into sterile plastic vessels immediately after the catch.

The feces of the birds was collected in sterile, one-way plastic tubes and transported to the institutes for microbiological and/or parasitological investigations.

The blood agar plates onto which the freshly caught flies had been placed were incubated at 37°C for 24 h. After the incubation, the petri dishes were checked for growth of microorganisms. For identification, the microorganisms were isolated and subcultured on blood agar and selective agar plates, and were finally incubated at 37°C for another 24 h. For identification of fungi, the microorganisms were isolated and were subcultured on Saboraud’s dextrose agar, and were then incubated at room temperature for 4 days. After the incubation period, the bacterial colonies were identified by standard bacteriological procedures (e.g., coagulase, oxidase test, Gram’s reaction, API^®, Prolex^®, VITEK^®, etc.). Isolated E. coli bacteria were identified for their pathogenicity by in-house real-time polymerase chain reaction, differentiating enterotoxic E. coli, enteropathogenic E. coli (EPEC), EHEC, and enteroaggregative E. coli.

The flies that were found close to the stables differed considerably with respect to their species relations from those found around dog meadows (Figs. 9.1–9.5). These differences are surely based on their different needs for different suitable breeding sites. Tables 9.3 and 9.4 summarize the occurrence of the different fly species at the different catching sites.

Around the stables, Musca domestica was the absolutely dominant species. In all catches in 3 years it was always present in the same relations:

In several cases its occurrence in poultry houses reached approximately 90%, which coincided with several important and massive fly outbreaks which were investigated by our group:

In all these cases the private houses up to a distance of 1 km were filled with hundreds of Musca domestica adults, which were apparently attracted by the dark interior of the houses when arriving from the surrounding fields, from the compost plant, and/or from badly stored chicken feces.

Practically in all cases the sex ratio of the flies caught was nearly 50:50 independent of whether the flies were caught close to the stables (i.e., outdoors) or inside houses.

The bloodsucking species Stomoxys calcitrans was an exception: only 42% of the flies caught outside were females. This might be attributable to the behavior of the females to suck blood and then to lay their eggs inside stables.

Tables 9.5 and 9.6 provide information on the life cycles of several important fly species, which of course primarily attack farm animals, but, however, also molest humans by often numerous touchdowns. During these contacts, agents of diseases (see Tables 9.1 and 9.2) may be placed on humans and their food too. In these cases the flies could become vectors of zoonotic agents of diseases (see also Sect. 9.5 and Chap. 10).

Tables 9.5 and 9.6 in addition show the periods when the flies are most active at the in general moderate temperatures of central Europe. In warmer regions they are active for practically the whole year, so the potential transmission of agents of diseases may occur throughout the year. This makes it clear that only strict prophylaxis measures will protect animals and as a consequence also humans who live in the close neighborhood of animals.

All flies caught in the surroundings of human dwellings and/or different animal houses or recreation sites are so-called synanthropic species (Sukopp and Wittig 1998). The definition of the term “synanthropy” characterizes plant or animal species which have adapted their life cycle to human housing areas. There they may reproduce in such high numbers that they do not need additions from outside to maintain their population at a constant level. In cases of an increase in food, many other individuals of this species might be attracted and this may lead to real plagues. Eusynanthropy and hemisynanthropy are subgroups of synanthropy. In the first case, the occurrence and reproduction of a certain species is obligatory because of the co-occurrence with human houses. Members of the genus Drosophila are examples of flies in Europe. Examples of other insects are the bedbug (Cimex lectularius), the bread beetle (Stegobium paniceum), and imported cockroaches (Blatta orientalis, Blattella germanica, Supella longipalpa, Periplaneta americana), which can only exist in human houses, whereas forest cockroaches (e.g., Ectobius silvestris) enter human dwellings only occasionally. “Hemisynanthropy” (the facultative form) covers species which find an optimum amount of food and facilities for survival inside or around human dwellings, but these species also survive easily outside human settlements. For example, Lucilia caesar is such an species as is the Eurasian swift (Apus apus), which likes to use human buildings as a starting point for its magnificent flights, although it may also start from natural rocks, etc.

With respect to these definitions of synanthropy, many flies are hemisynanthropic animals, which use the facilities of human settlements with all their garbage, superfluous food, and protected places for their—often immense—reproduction. They may, however, survive easily far away from human settlements, since dead animals, their carcasses, and their degrading feces offer practically unlimited food and propagation facilities. Therefore, even the best fly control measures cannot prevent the constant influx of flies from outside into human houses and into the stables of farmed animals. However, eusynanthropy and hemisynanthropy of most flies make it necessary for humans to control fly propagation by minimizing the breeding sites in and around human buildings of any kind. This can be done simply by reduction of garbage, removing remnant food, removing feces, changing straw, etc. In addition—especially in monocultures of many animals—chemical treatment of animals, of the stable walls, and/or of the straw might become necessary to prevent feeding farm animals from being disturbed or even to avoid infections with agents of diseases as listed in Tables 9.1 and 9.2.