Arxiu d'etiquetes: mites

Forensic entomology: arthropods at the crime scene

Unavoidably, every organism’s life comes to an end sooner or later. But where the cycle of life ends for some, others will find their opportunity to start a new life. Insects and other arthropods are some of the organisms that take advantage of dead animal rests to develop, and their study offers us valuable information to set the time, place and circumstances of someone’s death (something of special interest for criminologists). How is this information obtained from the study of arthropods? Keep reading to find out the answer.

Origins of forensic entomology

Forensic entomology is a branch of applied entomology that uses insects and other arthropods as scientific evidences to aid legal investigations; however, its most well-known use is the medicolegal one. Medicolegal forensic entomology is focused on the study of insects and other arthropods that inhabit decomposing remains or corpses to determine the time passed after their death, as well as to clear up the circumstances and determine the location where it took place. It’s a useful tool for criminologists since it can help to verify the alibi of a suspected assassin or to help in the identification of a victim.

Human skull with dermestid beetles. Public domain.

Forensic entomology is not a modern discipline. The concept of forensic entomology and the first case resolved by applying this discipline dates to at least the 13th century in China: the identity of the assassin of a farmer was discovered when all the suspected were gathered and forced to leave their sickles on the ground; then, flies were attracted only to one sickle, because it still had remains of blood and tissues on its edge.

Back then, the use of forensic entomology was anecdotal and their bases were not well-known. It was not until the 17th century that Francesco Redi refuted the “spontaneous generation” theory, which defended the idea that life comes from non-life (organic and inorganic matter) and that no causal agent is needed. Through different experiments, Redi proved something that seems us logical nowadays: life comes through life, so that insects that develop on corpses were already there before we noticed them (either as eggs or larvae).

Unconsciously, Redi’s experiments revealed some more facts: for example, that both location and climatology agents which a corpse is exposed to determine the composition and abundce of insect’s populations. This is very interesting since it helps us to find out the exact location where a death took place and if the corpse was moved to another place.

Historically, it was not until the 19th century that Bergeret, a French doctor, along with the discoveries of Orfila (who listed and described more than 30 insects and other arthropods which colonize dead bodies) and Redi, expanded and systemized forensic entomology. However, it’s considered that the true birth of this discipline took place at 1894, when J. P. Mégnin published his most famous paper: La faune des cadavres: Application l’entomologie a la medicine legale.

Uses and application of forensic entomology

When criminologists face a crime, they ask themselves three basic questions: ‘How’, ‘When’ and ‘Where’. Forensic entomology can respond correctly to those of the moment and place of death.


From a legal point of view, it’s essential to estimate the time elapsed since the victim’s death. This time lapse is known as Post-Mortem Interval (PMI). In human corpses, this interval can be estimated through three methods: histological (temperature, stiffness, cadaveric lividity…), chemical (measurement of the level of different chemicals) and zoological (animal action and insects’ invasion). Also, we must consider the deterioration level of plastic tissues, clothes, etc. However, after 72h the most efficient method to estimate de PMI is forensic entomology.

There exist two ways to estimate de PMI using arthropods:

  • Establishing the age and development rate of larvae. This method is mainly used at the first decomposition stages of dead bodies.
Calliphora sp. larvae on a dead body. Author: Hans Hillewaert, CC.
  • Establishing the composition and level of development of arthropods’ communities to be then compared with the natural patterns observed on near habitats. This method is mainly used at advanced stages of corpse decomposition.


The place of the death strongly determines the species of arthropods we can find in a dead body as well as the succession patterns of their communities. Among the most determinant parameters of arthropods’ communities’ composition we highlight the biogeographical region (species from tropical and temperate regions are almost never the same), the season (at median latitudes, seasonality has an important role on biological cycles) and the specific traits of the habitat (moisture, solar radiation, accessibility and exposition degree, etc.), which can make more or less easier the colonisation of arthropods and, consequently, to alter the PMI estimation.

Along this article, you will notice we only refer to terrestrial arthropods: this is due to the difficulty and complexity to determine the PMI and the place of death at marine habitats.

The main actors: the arthropods


Arthropods we can find in a corpse are classified in four main groups:

  • Necrophagous: they feed directly on dead remains and constitute the main group of arthropods we can find in a corpse. Necrophagous include basically dipterans (families Calliphoridae, Sarcophagidae, Muscidae, Phoridae…) and coleopterans (families Silphidae, Dermestidae…) .
  • Predators and parasites of necrophagous: they’re the second most relevant group of arthropods in a corpse. It is formed by coleopterans (families Silphidae, Staphylinidae, Histeridae), dipterans (families Calliphoridae, Stratiomydae) and parasitic hymenoptera of larvae and eggs of dipterans (e.g., Ichneumonidae) which were previously on the dead body.
  • Omnivorous: wasps, ants and coleopterans which feed both on body remains and remains of other arthropods.
  • Accidental species: those species that use the dead body as an extension of their own habitat, so that they greatly vary according the external conditions (collembola, spiders, millipedes and centipedes, mites, etc.).

To know more about organisms’ relationships, you can read ‘Symbiosis: relationships between living beings‘.

The corpse colonisation step by step

Despite the specific variations depending on each case, colonisation and succession of populations of arthropods in a corpse follow a quite constant pattern.

  1. Immediate principles degradation

Some dipterans (Calliphoridae and/or Sarcophagidae) feel attracted to gases expelled by the body during the first stages of decay (ammoniac, sulfhydric acid, nitrogen, carbon dioxide). Then, they lay their eggs inside natural holes (eyes, nose and mouth), in wounds or on the surface in contact with the substract, which has a high moisture level due to the accumulation of bodily fluids. However, their sense of smell is so developed that they sometimes land on the body when the person is still alive, especially when it has open wounds!

You can learn more about insects communication and senses through the article “How do insects communicate?“.

We rarely see these two families coexisting at the same time in a corpse, probably due to the fact Sacrophagidae larvae prey on the ones of Calliphoridae.

Calliphora vicina (left); Sarcophaga carnaria (right). Authors: AJC1, CC; James K. Lindsey, CC.

Is essential to know the development degree of larvae and pupae of each species, as well as their length of their life cycles and their specific traits to estimate the PMI. These parameters may vary among the species, also due to the external conditions and/or the death circumstances; moreover, their presence is so common that their absence can result informative as well.

 2. Butyric fermentation of fat

When fermentation of fats begins, there appear the first coleopterans (Dermestidae) and lepidopterans (e.g. the moth Aglossa pinguinalis), being very common in one month old corpses. While Dermestidae life cycle lasts 4-6 weeks (larvae feed on fats and moults of preview arthropods), the one of lepidopterans such as A. pinguinalis can last until the next spring if external temperatures are not adequate for their development.

Dermestes maculata (left); Aglossa pinguinalis (right). Authors: Udo Schmidt, CC; Ben Sale, CC.

 3. Caseic fermentation of proteins

During this stage of the body decay, there appear dipterans which are also very common during other fermentation processes, such as the one of cheese or ham (Piophila sp., Fannia sp., as well as Drosophilae, Sepsidae and Sphaeroceridae genres). There also appear coleopterans of the genus Necrobia.

Piophilia casei (left); Necrobia violacea (right). Authors: John Curtis, Dominio Público; Siga, CC.

 4. Ammoniacal fermentation

During this stage, there appear the last dipterans (genus Ophira and family Phoridae, essentialy), which can be found inside bird nests or lairs feeding on animal remains, excrements and organic wastes from their hosts. There also appear different groups of necrophagous coleopterans of the genera Nicrophorus, Necrodes and Silpha, very common during advanced decay stages, and predator coleopterans of the families Staphylinidae (genera Coprohilus, Omalium and Creophilus) and Histeridae (genera Hister and Saprinus).

Nicrophorus humator (left); Coprophilus striatulus (right). Authors: Kulac, CC; Udo Schmidt, CC.

 5. Disappearance of rests

After more than 6 months, the corpse is almost totally dry. In this moment, there appear a huge number of mites of different species that feed on mildew and fungi covering the rests. Posteriorly, there also appear coleopterans that feed on hair rests and nails (Dermestes, Attagenus, Rhizophagus, etc.), some Dermestidae species present on previous stages and some lepidoterans.

After more than a year, the scarce rests are sometimes attacked by coleopterans of the genera Ptinus, Torx and Tenebrio.

Tenebrio obscurus. Author: NobbiP, CC.

.           .           .

Forensic entomology is just one example of how useful can be to study insects and other arthropods both from a taxonomical and an ecological point of view. However, there exist many more applications. Do you know them or want to learn about them? You can leave your suggestions and curious facts on the comments’ section below.


  • Entomología Forense. Colegio de Postgraduados.
  • Joseph, I., Mathew, D. G., Sathyan, P., & Vargheese, G. (2011). The use of insects in forensic investigations: An overview on the scope of forensic entomology. Journal of forensic dental sciences, 3(2): 89.
  • Magaña, C. (2001). La entomología forense y su aplicación a la medicina legal. Data de la muerte. Boletín de la Sociedad Entomológica Aragonesa, 28(49): 161.

Main photo made by the author of this post using different images (fly vector dessigned by Freepik on with a licence CC 3.0 BY).

Home’s micro-squatters

If you ever thought to be alone in your house, you were wrong. In your home there are thousands and thousands of micro-organisms sprout at ease. They are responsible for odors and pollution from yourhome. Would you like to know more about your tenants?


It is stimated that about 90% if our time is spended in closed places, such as office, school or home. These places, as well as the rest of our planet, presents a environmental conditions suitable for proliferation of bacteria, fungi and arthropods. These communities are known as the Home’s Microbiome.

Photomicrograph of the bristle of a used toothbrush where proliferate a lot of microbial communities (Image: Science photo library)

The relations that we stablish with these communities of microorganisms can condition directly in our health. Can find beneficial microorganisms, indifferent microorganisms (i.e that do not produce any effect) and pathogenic microorganism (as Staphylococcus auereus resistant to antibiotics) or allergens as them mites. These pathogens, in most of cases, just represent a litle percentage and not pose any risk for them home’s occupants.


Bacterial communities are very abundant in our homes. We can find them in every corner and have a great diversity. For example, in the dust is estimated that there are som 7000 different bacterial species. In the following graphic, can observe the broad diversity of bacterial species that colonizes certain regions of our home, such as the toilet’s lid, kitchen or our own beds.

Differents bacterial families that we can found arround our home (Image: G.E. Flores)


In normal conditions, a house can present up to 2000 different types from fungi. We can also find them in all home environment such as food, kitchen, walls and even in forgotten places during cleaning as for example the dust accumulated on the door frames. Among them, we can highlight the presence of Aspergillus, Penicillium and Fusarium (common envirnmental fungi). Also proliferate fungi responsible of the wood degradation (as for example Stereum, Tremetes, or Tremellosa) or fungi related with humans, like Candida.

Wall mold that appear in homes (Image: or fruit mold by Penicillium sp. (image: wisegeek).


These microorganisms represents to the Arthropods of our homes. Normally they live in dust, on rough surfaces such as fabrics, mattresses and pillowsa where they feed on died human and animals skin. We can find Dermatophagoides pteronyssus and Dermatophagoides farinae species, commonly knwon as dust mites. Even so, and to a lesser extent, we can find also some that another exemplay of Demodex folliculorum. This mite live in the hair follicles of our face and feeds on dead skin. Normally follows from the skin while we are sleeping.

Dust mite D. pteronyssinus (image: Göran Malmberg) and follicles mite Demodex folliculorum (Image: BBC)


The geographical distribution of these microscopic communities and those factors that determine it, are little known. For that reason, along this decade, studies about hom’s microbiome have increased and proliferated singnicantly.

The large microbial diversity changes over different locations in our home, i.e. we will not find the same microorganisms in bed than in the bowl of the toilet. For example, in our kitchen, depending on the place that we examine, we find greater abundance of specific bacterium or other. In the image bottom, us show as in the stove of our kitchen find more Salmonella sp than Clostridium sp.

Differences in the abundance of bacteria depending on the location (Image: G.E. Flores)

Even so, we can found a certain pater in this distribution, i.e. the microorganisms that inhabit certain areas are more similar than the comminities that we found in other locations. In the following dendogram we can observe that microorganisms found in our pillowcase are very similar to those that found in toilet, but completely different from whichwe can find in our kitchen cutting board.

Dendrogram of similarity between the bacterial communities of various areas of our home. (Image: Robert, D. Dunn).

But, what is the reason for this geographical distribution?

The response is found in the differents emission sources of these organisms. Depending on the source we can find find a few species or others. Obviously the main microorganism source of emission  into the environment are humans. We know that millions of bacteria and other microorganisms live in our body and they spread everywhere, either by respiratory activity, waste digestion or skin contact. Each human leaves a specific microbial fingerprint in those places. 

Major sources of emissions according to the area of the home to examine. See is that the largest source of emission are the own human. (Image: G. E. Flores)

In the graphic you can see that in some places appear microorganisms related to our intestines, specifically those who are ejecting with droppings. Is not wash you hans after going to the service, surely yo go spreading faecal bacteria everywhere. Also, if you pull the string with the toiled lid open, it causes the expansion of faecal bacteria as if it were a spray, reaching our toothbrushes  or the hand soap.

On the other hand, microbial diversity is very influenced by the number and type of home occupants. We cannot found the same microorganisms in a house with two persons than in other one with a family of seven. In addition, is has observed that not found the same microorganisms in homes where there is greater number of women that in which there is greater numer of males. Usually, mens released more microorganisms to environment.

Graphic of the influence of the genre of the occupants in the diversity of microorganisms in our home (Image: Albert barberán).

Another important factor that determines this geographical distribution and microbial diversity is the presence of pets. If in our homes we have animals like cats or dogs, we will found more varied microbial communities. In these case, these microorganisms are related to feces, skin and glans of these animals.

Differences in the abundance of certain bacterial species based on the presence or absence of pets (Image: Albert barberán).

Although the main source of emission are the occupants of these homes, microscopic comminities that colonise all corners are closely related to which we can found on the outside. In the case of fungi, this relationship is more narrow that in the case of bacteria. Even so, it has been observed that species are more varied in houses.

Comparison of the rich bacterial and fungal of our homes and the foreign. (Image: Albert barberán)


How much reason have the phrase “as my home any place! Each home is indeed aunique and specific universe of microscopic communities. There aren’t two equal in the world!



Rapinyaires nocturnes: l’òliba, les seves llegendes i mites

Les rapinyaires nocturnes han patit des de temps immemorials una injusta mala fama, que les ha portat en alguns casos a ser perseguides i odiades. Quines són aquestes supersticions? Quin és el seu estat de conservació? Què pots fer tu per elles? En aquest article descobriràs a les rapinyaires nocturnes i a l’òliba comuna (potser l’espècie més arrelada en el nostre imaginari) i les llegendes associades a ella.


Com el seu nom indica, les majoria de rapinyaires nocturnes (òlibes, mussols, gamarussos) tenen hàbits nocturns o crepusculars. Són carnívores, amb uns becs i urpes (dos dits cap endavant i dos cap enrere) adaptats per esquinçar la carn de les seves preses (petits mamífers, aus, rèptils, grans insectes ).


Les rapinyaires nocturnes tenen generalment una forma arrodonida i un aparent gran cap, amb les plomes de la cara formant l’anomenat disc facial. El disc facial fa les funcions d’antena parabòlica dirigint els sons cap les oïdes. L’obertura de l’orella és de grans dimensions i amb un plec de pell (halda preaural), que funciona com un pavelló auditiu i és mòbil com en alguns mamífers.

Oído de lechuza norteña (Aegolius acadicus). (Foto tomada de Jim McCormac).
Orella de mussol acadià (Aegolius acadicus). (Foto de Jim McCormac).

La posició de cada orella és asimètrica en algunes espècies (una està més alta que l’altra), de manera que algunes -com l’òliba- poden localitzar preses en la més absoluta foscor: una orella percep el so abans que l’altra, de manera que el seu cervell pot calcular el lloc exacte on està la presa (escolta direccional).

Boreal owl skull, cráneo de mochuelo boreal
Crani de mussol pirinenc (Aegolius funereus) on s’aprecien les obertures auditives asimètriques i els anells escleròtics oculars. (Foto presa de Jim Williams)


La visió de les nocturnes està molt desenvolupada. Els ulls, a diferència de la majoria de les aus, estan en posició frontal, cosa que els permet un càlcul perfecte de la profunditat i visió tridimensional. Per contra, són tubulars (no són esfèrics com els nostres) a causa de la gran grandària de la còrnia i lent, cosa que els impedeix moure els ulls dins de les conques. A més, posseeixen un anell ossi protector al voltant dels ulls (anells escleròtics) que també impedeixen el moviment. Per solucionar aquest problema, són capaces de girar el cap fins a 270 graus. Es pot considerar que veuen en blanc i negre (perceben millor canvis de llum que colors), la pupil·la es dilata moltíssim en condicions de poca llum (l’iris queda ocult) i són les úniques aus en que la parpella es tanca de dalt a baix. També posseeixen un parpella” transparent que humiteja i protegeix l’ull, anomenada membrana nictitant.

Visión lechuza, binocular, vista, búho, razces nocturnas
Visió binocular d’una rapinyaire nocturna. Els humans tenim un camp de visió de 180 graus (140 dels quals son visió binocular). (Imatge de The Owl Pages)


Les rapinyaires nocturnes, a diferència de les diürnes, tenen unes plomes de vol amb una estructura especial, amb serrells (barbicel·les) a la superfície superior i contorn. La fricció entre elles i amb l’aire queda esmorteïda, aconseguint un espectacular vol silenciós impossible de detectar per les preses.

Pluma de lechuza común y autillo, donde se observan las barbicelas. (Foto tomada de Pedro Montoya).
Ploma d’òliba (Tyto alba) i xot ( Otus scops),on s’observen les barbicel·les. (Foto presa de Pedro Montoya).


L’òliba (també anomenada  xibeca, babeca, meuca o mifa), Tyto alba, és inconfusible: posseeix un disc facial de color blanquinós, molt ben delimitat i en forma de cor. El dors és de color gris amb taques daurades i fins punts blancs i negres.


Viu en gran part del món (exceptuant l’Antàrtida, nord i est d’Europa i gairebé tota Àsia) en camps oberts, sovint conreats. No construeix niu, sinó que posa els ous en forats d’arbres, forats a la roca o en edificacions humanes (graners, golfes, masies, castells, esglésies ).

Per què l’òliba té aquesta fama negativa que ha provocat la seva persecució en molts llocs del món i d’Espanya? Les causes són diverses, alimentades totes per la por humana:

  • Poden nidificar en llocs abandonats o sagrats com esglésies (algunes amb el seu respectiu cementiri).
  • Hàbits nocturns
  • Són sendentàries, poden quedar-se al mateix vedat de caça durant anys fins que l’aliment escasseja.
  • Aspecte fantasmal a causa dels seus colors i vol suau i sigilós.
  • Per les seves vocalitzacions (en tenen 17 de diferents) semblants a crits humans i esbufecs peculiars. Escolta unes òlibes defensant-se en el següent vídeo:


A la Península ibèrica es creia que les òlibes es bevien l’oli dels llums de les esglésies, deixant els sants a les fosques (quan els veritables lladres eren els sagristans). En posar-se sobre els llums o fregar i vessar l’oli, es creia que odiaven la llum, com si fossin esperits malignes. De fet,  el seu nom en català, òliba, fa referència a aquest mite. Van ser caçades i penjades mortes de les portes de les esglésies i graners per espantar al foc i el llamp.

Les vocalitzacions de les òlibes també s’interpreten com anuncis de la mort, i hi ha la creença (sense cap fonament) que si se sent una durant diverses nits seguides (cosa gens difícil, atesos els seus hàbits sedentaris) una persona perdrà aviat la vida.

Tyto alba, lechuza común, lechuza de campanario
Òliba (Tyto Alba). (Foto de Kerkuil André).

En altres cultures també existeixen llegendes negatives sobre les nocturnes en general: a Àfrica que són enviades per bruixots per matar gent o dimonis malignes que anuncien desastres, en les pampes argentines que són germanes del dimoni, a Sicília, mort o malaltia, a Xile, bruixes que es metamorfosejaven per celebrar aquelarres per totes aquestes raons han estat assassinades i torturades.

Tot i això, també gaudeixen de llegendes agradables (com ser guardianes de les dones que moren, a Austràlia), encara que el cas més conegut és la representació d’Atenea, deessa grega de la saviesa. Actualment encara apareix com a símbol de nombroses institucions o monedes com l’euro grec.

Euro grecia, euro griego
Euro grec. (Font: RTVE)


Actualment l’òliba es troba en estat de retrocés i amb un futur incert a causa de les transformacions introduïdes pels humans en el medi rural, com els canvis de cultiu o l’ús de pesticides i rodenticides, que causen la mort de les seves preses (ratolins) o indirectament de les aus mateixes. Les obres i remodelacions d’edificis on solien nidificar també interfereixen en la seva reproducció. Sol ser un au habitualment atropellada, sobretot els joves en dispersió. També pateixen accidents a causa de les torres i cables d’alta tensió. La subespècie canària (Tyto alba gracilirostris) està desapareixent per la fragmentació d’hàbitats i el baix nombre d’individus de les seves poblacions.

Lechuza muerta
Òliba en un filferro d’espines. (Foto de PacoT).

Està catalogada com En perillen el Llibre Vermell de les aus d’Espanya i inclosa en el Catàleg Nacional d’Espècies Amenaçades en la categoria D’interès especial“.


Tracta d’informar-te sobre aquestes magnífiques aus i dóna-les a conèixer en el teu entorn proper desterrant falsos mites, sobretot si vius a prop de les seves zones de nidificació i alimentació. Si tens cultius, intenta minimitzar l’ús de plaguicides: una parella d’òlibes cacen de mitjana uns 2000 ratolins a l’any, sent per tant beneficioses fins i tot per als humans.

Si trobes una òliba o qualsevol au ferida, cal recollir-la amb cura (utilitzant una tovallola o jaqueta) per evitar ferir-la o que ens faci mal a nosaltres i deixar-la en un lloc fosc i tranquil dins d’una caixa foradada perquè pugui respirar. No se li ha de donar menjar. A continuació posa’t en contacte amb un centre de recuperació de fauna salvatge de la teva regió.


Si t’ha agradat aquest article, si us plau comparteix-lo a les xarxes socials per a fer-ne difusió,  doncs l’objectiu del blog, al cap i a la fi, és divulgar la ciència i que arribi al màxim de gent possible. T’animem també a comentar les teves experiències amb les aus rapinyaires. Coneixes a algú que encara cregui en aquestes llegendes? N’havies sentit a parlar mai d’elles?

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