Vänerns stränder håller på att växa igen av buskar, träd och vass, detta hotar den biologiska mångfalden runt sjön Många vikar och sund täcks av vass och detta är en stor orsak till att de hotade arterna får svårt att överleva, möjliga orsaker till igenväxning är ökat kvävenedfall, markdeponerat kväve från jordbruk, minskad skötsel i form av bete eller slåtter samt reglering av vattenståndet i sjön. Många arter kräver en öppen solbelyst miljö för sin överlevnad, så även Liten myrlejonslända (Myrmeleon bore) som kan fungera som en indikator för hög biologisk mångfald. Syftet med denna rapport är att ge en bild av vilka faktorer i naturen som gynnar liten myrlejonslända. Detta för att eventuellt kunna bidra med underlag vid vidare arbete med restaurering av Vänerns stränder och omgivande mark. Liten myrlejonslända föredrar torra väl solexponerade sandslänter i söderläge där den finns en bit upp från strandkanten. Inventeringen av larver av Liten myrlejonslända på stränder gjordes med hjälp av linjetransekter med 2 meters mellanrum, där man räknar fångstgroparna som byggs av myrlejonsländans larver. De miljövariabler som mättes i undersökningen för att kunna se ett eventuellt samband med förekomsten av Liten myrlejonslända var trädtäthet, väderstreck på stranden, avstånd till annan strand med förekomst av Liten myrlejonslända, kornstorlek, lutningen av stranden, andel blottad sand på stranden, andel vegetation på stranden samt förekomst av tall i strandområdet. Analysen visar att den viktigaste förklaringsfaktorn för förekomst av Liten myrlejonslända är närhet till annan strand där det förekommer Liten myrlejonslända. Som förklaringar till variationer i tätheten hos Liten myrlejonslända finns sluttning på stranden främst följt av andelen blottad sand på stranden. / The beaches of Lake Vänern in Sweden are in a stage of being overgrown by bushes, trees and reeds. Today many of the bays and channels are covered with reeds, and this is one of the main reasons for the loss of species around the beaches of Lake Vänern. Causes that may be affecting, for example, increased nitrogen deposition, increased amounts of ground deposited agricultural nitrogen, reduced maintenance in the form of grazing or mowing, and also the fact that the water levels are being regulated in the lake which reduces the natural fluctuations that may otherwise contribute to a more open beach environment. Many species are dependent of an open sunlit area for their survival and amongst them is the small antlion (Myrmeleon bore), who can serve as an indicator species for the biodiversity of an area. The purpose of this report is to provide a frame of what factors in nature that favors small antlion. This is to possibly provide a basis for further work on the restoration of the shores of Lake Vänern and surrounding land. The small antlion prefers dry, well sunlit sand slopes, where it can be found somewhat uphill from the shoreline. The inventory of larvae of small antlion on beaches were made using line transects with 2 meter intervals, from where the conical traps built by the antlions where counted. The environment variables that were measured in the survey in order to see a possible link with the presence of small antlion was tree density, cardinal on the beach, distance to another beach with the presence of small myrlejonslända, grain size, the slope of the beach, proportion exposed sand on the beach, proportion of vegetation on the beach and the presence of pine in the beach area. The analysis shows that the most important explanatory factor for the occurrence of small antlions is proximity to another beach where there are small antlions. As explanations for variations in the density of small antlions, slope of the beach was number one followed by the proportion of bare sand on the beach.

1) An investigation was undertaken into the various activity rhythms found in the larvae of Myrmeleon obscurus (Neuroptera, Myrmeleontidae). Pit construction was used as the criterion of activity. 2) The capacity sensitive electronic circuit used to monitor the daily pit building activity is described. 3) Various factors affecting the size of the pits constructed by ant-lion larvae were investigated. Pit size was found to be correlated with the size of the larvae, larger larvae constructing bigger pits. Population size was also shown to have an effect, since the more crowded the animals were the smaller and closer together their pits became. The death rate due to competition between the larvae also increased as the ant-lions became more crowded. 4) Feeding frequency also affected pit size. Ant-lions which were starved constructed very small pits. 5) Pit size was affected by the texture of the sand, maximal pit size being attained in sand with a grain size of between 353 μ and 211 μ. This was shown to be the most abundant grain size in sand from the natural habitat. In sand coarser or finer than this, pit size was reduced. 6) Generally smaller pits were constructed at lower temperatures, but this response depended largely on the lunar cycle. The upper and lower critical limits for pit construction were found to be 11° C and 42° C. Below and above these temperatures no pits were constructed, although the ant-lions remained alive. 7) Daily destruction of the pits decreased the pit size. 8) The existence of the daily pit building activity rhythm, which occurs at dusk, was demonstrated in individuals and in populations of ant-lion larvae. This rhythm was studied using the capacity sensitive circuit, and also by direct observation of groups of animals over a 24 hour period. 9) The daily activity rhythm appeared to be endogenous, since it continued for at least a month both in constant light and in constant dark. The rhythm was altered by reversals in the daily light-dark cycle, and it was concluded that light was the main phase setting factor. 10) An attempt was made to determine the location of the "clock" or "clocks" controlling the daily activity rhythm. This was investigated by chilling the heads of individual ant-lions with a fine copper wire, and also by chilling large groups of animals in the refrigerator. From these experiments no definite conclusions could be drawn about the location of the "clock". 11) The existence of a lunar pit building cycle was demonstrated in both field and laboratory populations of ant-lions. Maximal pit size was attained at full moon. Very low temperatures were found to suppress these lunar peaks. 12) The lunar pit building rhythm was shown to be endogenous, since it continued for at least two months in constant dark and one month in constant light. 13) The lunar pit building rhythm of very young larvae was investigated, and it was shown that while larvae which hatched in the field appeared to possess a lunar rhythm, larvae which were hatched in the laboratory did not have a rhythm. It was therefore concluded that the light of the moon was necessary to establish the lunar rhythm. 14) Some possible explanations for the lunar cycle were investigated experimentally. It was concluded that the lunar rhythm was not related to the number of prey present at various times of the lunar cycle or to the spacing of the animals in their habitat. The lunar rhythm was shown to be due to the combination of a lunar day activity rhythm and a solar day activity rhythm. 15) Some aspects of the daily rhythm are discussed, and this rhythm is compared with those found in other insects. Probable functional reasons for the rhythm are presented. Summary, p. 133-136.

Nach dem Erstnachweis von Myrmeleon-Bohrungen (Tjeder, 1941) in der Dresdner Heide im Jahr 2019 (KURTH 2020, Sächs. Entomol. Z. 10: 71-80) wurde die Populationsgröße und Dichte der Art bestimmt. M. bore wurde hauptsächlich in offenen, spärlich bewachsenen, sandigen Gebieten mit direkter Sonneneinstrahlung gefunden. Die flächengewichtete Dichte des gesamten Untersuchungsgebietes (4,05 Hektar) betrug 0,177 Larven/m2. Schätzungen der Populationsgröße basierend auf zufälligen Quadratzahlen führen zu einer Zahl von 4000-7000 Individuen - die größte bekannte Population dieser Art. Die für diese Art aus Laborversuchen bekannte positive Korrelation zwischen Larvengröße und Grubendurchmesser wurde an unserem Studienstandort bestätigt. Diese Korrelation könnte es Forschern ermöglichen, die Altersstruktur von Wildpopulationen abzuschätzen. Angesichts der besonderen Verantwortung Deutschlands für den Schutz dieser Art und der Größe der Population fordern wir den Schutz des Gebietes und eine Priorisierung gegenüber anderen geschützten Arten in diesem Gebiet. / Following the first record of Myrmeleon bore (Tjeder, 1941) in the Dresden Heath area in 2019 (KURTH 2020, Sächs. Entomol. Z. 10: 71-80), the population size and density of the species was determined. M. bore mainly was found in open, sparsely vegetated, sandy areas with direct sunlight exposure. The area-weighted density of the entire study site (4.05 hectares) was 0.177 larvae/m2. Population size estimates based on random quadrat counts lead to a figure of 4000-7000 individuals - the largest known population of this species. The positive correlation between larval size and pit diameter known for this species from laboratory trials was confirmed at our study site. This correlation may allow researchers to estimate the age structure of wild populations. Given the special responsibility of Germany for the protection of this species and the size of the population, we urge the protection of the site and a prioritisation over other protected species found in the area.