Early colonisation of urban indoor carcasses by blow flies (Diptera: Calliphoridae): An experimental study from central Spain
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Published on: November 17, 2023
Daniel Martín-Vega1, Carla Martín Nieto2, Blanca Cifrián2
1Departamento de Ciencias de la Vida, Universidad de Alcalá, 28805 Alcalá de Henares, Madrid, Spain; Department of Life Sciences, Natural History Museum, London SW7 5BD, United Kingdom.
Abstract:
Due to their ubiquity and synanthropy, blow flies (Diptera: Calliphoridae) are generally the first colonisers of cadavers and, therefore, frequently used to estimate a minimum post-mortem interval (minPMI). Whereas in outdoor situations blow flies are expected to locate and colonise exposed cadavers within hours or even minutes after death, it is usually assumed that the colonisation of a cadaver indoors might be delayed for an uncertain period of time. This uncertainty severely limits the informativity of minPMI estimates based on entomological evidence. Moreover, these limitations are emphasised by the lack of experimental data on insect colonisation of indoor carrion and by the fact that most of the forensic cases involving entomological evidence have been reported to occur indoors. In this study we investigate the early colonisation of pig carcasses placed indoors in a building located in the centre of an urban environment in central Spain. Three carcasses were placed in three equal rooms with a window half opened during five experimental trials: summer 2013, autumn 2013, winter 2014, spring 2014 and summer 2014. The species composition and their contribution to the carrion colonisation differed among seasons. Calliphora vicina Robineau-Desvoidy was the sole coloniser of carcasses in winter and colonised the carcasses within the first 24-48h in every season, although Lucilia sericata (Meigen) was the first coloniser of most summer carcasses. On the other hand, Calliphora vomitoria (L.) and Chrysomya albiceps (Wiedemann) colonised the carcasses significantly later in spring and in spring and summer, respectively, with a delay of several days. In autumn, however, there were no significant differences in the colonisation times by C. vicina, L. sericata and Ch. albiceps. C. vicina and L. sericata showed a clear preference for ovipositing in the natural orifices of the carcasses, whereas Ch. albiceps oviposited more frequently on the trunk and legs.
Insights
Blow flies colonize indoor carcasses rapidly, with Calliphora vicina being a consistent early arrival across seasons. This study provides crucial data for estimating post-mortem intervals in indoor forensic cases.
Area of Science:
- Forensic Entomology
- Ecological Studies
- Urban Entomology
Background:
- Blow flies are key indicators for estimating minimum post-mortem intervals (minPMI).
- Indoor carrion colonization timing is poorly understood, limiting forensic entomology applications.
- Most forensic cases occur indoors, highlighting the need for indoor colonization data.
Purpose of the Study:
- To investigate the early colonization patterns of blow flies on indoor pig carcasses.
- To determine seasonal variations in blow fly species composition and colonization times indoors.
- To provide experimental data for improving indoor minPMI estimations.
Main Methods:
- Placement of pig carcasses in three indoor rooms with partially open windows.
- Conducting five experimental trials across different seasons (summer, autumn, winter, spring).
- Monitoring and recording species composition, colonization times, and oviposition sites.
Main Results:
- Species composition and colonization timing varied significantly by season.
- Calliphora vicina consistently colonized carcasses within 24-48 hours, even in winter.
- Lucilia sericata was the primary colonizer in summer, while Calliphora vomitoria and Chrysomya albiceps showed delayed colonization.
- Chrysomya albiceps exhibited different oviposition preferences compared to C. vicina and L. sericata.
Conclusions:
- Blow fly colonization of indoor carrion is relatively rapid, challenging previous assumptions of significant delays.
- Calliphora vicina is a reliable early colonizer indoors across seasons.
- Seasonal data on blow fly activity and oviposition behavior are crucial for accurate indoor forensic entomology.
