INTO THE SECOND WEEK OF DECOMPOSITION

Decomposition has really progressed here during the early part of the second week the bear has been out! The maggots have grown, and huge numbers are reducing the mass of the bear. In general, we have seen a predictable sequence of insect species. However, a few surprises have come up! Here is what we found during 29 and 30 May 2007....

29 May 2007: Overall, the maggot numbers and size of individual maggots have increased. Adult fly activity is still heavy.

29 May 2007: The head is still a site for a lot of activity...

29 May 2007: Feeding by maggots have begun to expose the skeleton of the bear's hind leg.

30 May 2007: The maggot mass has increased dramatically. There are 10's of thousands of maggots throughout the abdomen and thorax, as well as the orifices of the head. Adult fly activity is heavy. Beetles (Staphylinidae, Histeridae, Silphidae) are common.

30 May 2007: The head is still very active. Note to the left of the nose is a large (about 1 inch in length) carpenter bee - similar to a bumble bee. Up to 3 individuals have been observed around the nose and mouth sipping decompositional fluids. This is probably an excellent nitrogen source. These insects only became apparent at the carcass near the end of the first week of decomp.

30 May 2007: The maggot mass is huge! You can hear it when close up. These are mostly maggots in the third (final) instar, or stage of larval development. They are widespread throughout the carcass. Many have apparenetly embedded themselves into the surface of the skin and require a quick pull to free them from the carcass for collection. The stench present emits what I feel is almost an ammonia-like smell on top of the pungent odor of decay.

30 May 2007: An interesting aspect of maggot biology is the "post-feeding" stage. After getting a full gut, maggots move off a carcass (or corpse) to find a remote area to burrow into the soil where they form the pupa. This is a good life strategy as many larger scavengers such as coyotes and raccoons engulf maggots when chowing down on the soft tissues... The photo above shows several maggots outside the exclosure. Hundreds of maggots were found by lightly scraping the soil surface around the exclosure.

BLACK BEAR DECOMPOSITION - WEEK 1

We have been observing the bear, collecting insects, and rearing maggots for a week now. We have watched the bear and the insects change through time.
The bear has gone through phases of being very stiff and rigid to becoming more 'relaxed' as decompostion progresses. The stench is overwhelming. The skin has begun to slough off the body due to the action of the 10's of thousands of maggots present.

The insects have changed as well. The first arriver was a green bottle fly (Phaenicia sericata), a very common blow fly. They laid eggs quickly. The black blow fly (Phormia regina) came next, followed by cheese-skipper (Piophilidae) and black scavenger (Sepsidae) flies.

See our Forensic Insect Photo Atlas for some pictures of these flies:
http://www.cmnh.org/site/ResearchandCollections_InvertebrateZoology_Research_ForensicEnt_ForensicPhotoAtlas.aspx


We have hundreds of maggots being reared on beef in a small enclosure about 100 feet from the bear. We keep the insects there so the stench of decaying meat doesn't foul our lab and generate protests from colleagues. We also keep them in an outdoor enclosure so we can easily follow their growth and development at the same temperatures the bear and its insect community are exposed to.



HERE ARE SOME PHOTOS OF THE FIRST WEEK OF DECOMPOSITION:



22 May 2007: Laura Bock, a student of the Cleveland Institute of Art and a Museum summer intern, erects an exclosure around the bear to deter large scavengers. We thank the Kirtlandia Adopt-A-Student program for providing funds for Laura and her work!

22 May 2007: The bear during its first hours exposed to insect activity. Note that it is in a cage (or exclosure) to prevent large scavengers such as coyote from disturbing the study.

22 May 2007: The bear in its exclosure. It is positioned at the edge (or ecotone) between an open goldenrod field and a forest fragment composed mainly of wild black cherry. This is fairly typical habitat for black bear.

24 May 2007: The first colonizers... Blow flies arrived quickly and laid eggs. Within two days, we noted these maggot masses in the nostrils. There were also maggots in the mouth and around the anus. Openings to bodies and carcasses are the first places flies lay eggs. The tissue is soft, and there is moisture there that prevents the soft-bodied maggots from desiccating...

25 May 2007: The debris on the bear is just leaf-fall. Note the sticky trap next to the paw. It is just a cardboard sheet with a sticky material on it to capture flies. Each of those dots on the sticky trap is a fly! Hundreds were attracted to the bear. The sticky trap gives us an idea of what fly species are attracted to the bear. New traps are placed out daily...

26 May 2007: It doesn't look like much has changed since yesterday, but note the slight change in postion of the head to the photo above. Most of the action is taking place within the head and anus, out of view. The head is shifting because the decomposition of the musculature, as well as its consumption by maggots, will cause the animal to "relax" somewhat.

28 May 2007: Again, not much looks too different, but note the tail is pulling back from the body due to maggot action. The whitish material seen under the chin is frass, or insect excrement (yes, maggots poop) from those feeding in the nostrils and inside the mouth.

28 May 2007: Six days into decomposition, things are really moving... The skin is sloughing from the body. A huge maggot mass has accumulated around the anus/genitalia/abdomen. The nostrils, mouth, and ears are stuffed with blow fly maggots. Hundreds of flies (families Calliphoridae, Muscidae, Piophilidae, Sepsidae, and Phoridae) are still active. Many of the maggots are approaching full growth. See our blow fly life cycle diagram at:

http://www.cmnh.org/site/ResearchandCollections_InvertebrateZoology_Research_ForensicEnt_ForensicBlowfly.aspx

Note that the daytime temperatures are reaching the high 70s to mid 80s F, while night temps have dropped as low as 50F.

28 May 2007: Note that the skin is sloughing off the body below the chin.

28 May 2007: This is the maggot mass that was generated around the abdomen at day six. A blow fly can lay 100 eggs or more. When these maggots mature in a few days, they will wander off the carcass to find a safe place in the soil to form the pupal stage. Once they do that, we suspect it will take some 5-7 days before an adult fly is liberated from the pupal skin (or more technically, the puparium).

WHY AND HOW WE STUDY DECOMPOSITION

Why we are doing this...

We will observe and record the comparative decompositional patterns of pigs (standard animal used in decomp studies) and a black bear (Ursus americanus). While swine is often used to simulate human decompostion (during forensic research), bears are physically different than pigs (fur, size, body cavity, etc.) and may have different decompositional patterns and insect visitation dynamics. These data may then be applied to any future cases involving poaching of black bear in this part of the US. At the conclusion of the study, the bones of the animals and the insects collected will be accessioned into the CMNH collections.

How do we do this?

1. MAKE DAILY OBSERVATIONS

We record visual observations and photograph the carcass daily. We note insect activity, and the degree of decomposition for that day. We also record hourly temperature which we can use to calculate insect growth rates.

2. COLLECT INSECTS

We collect representatives of the insect community daily during the first few weeks. An insect succession will take place - in other words, the insect species on the carcass will change through time. By noting the insects present, we can document the succession which will possibly provide some data for determining how long a carcass has been dead.

Maggots are the most important insect specimens, particularly those of blow flies (family Calliphoridae). They are attracted to carcasses (and human corpses) very quickly, often within a few minutes or hours following death. They begin to lay eggs, and the maggots that hatch from the eggs provide a wealth of information of time since death (also known as postmortem interval).

We also conduct rearings of immature insects, particularly maggots, to the adult stage to facilitate their identification. Adult insects are relatively easy for the trained expert to identify, but maggots can be challenging. Having adults is handy... We can also study the growth and development of the flies collected. As we can expect several species of blow fly to be present (and each has its own development rate), a species-level identification is needed.

3. ANALYZE THE DATA

Basically, at the end of the decompositional process where only a skeleton remains, we can pull together our data to show the insect succession and the rates of development for the species present. With these data, a wildlife official can show us a poached bear and if insects are present, we can give an accurate estimation of the time of death. This can provide important supporting information during poaching investigations.

Black Bear Decomposition and Wildlife Poaching: How Insects Help Investigations

The poaching of wildlife is an age-old problem that continues today. Black bear are harvested for meat, and their gall bladders are taken for their use in creating traditional medicines. The species is endangered in Ohio, and it is illegal to harvest them.

To date, data are lacking on the use of insects to determine the approximate time of death of a poached animal. The use of forensic entomology has been used extensively to assist in human death under mysterious or suspicious circumstances (See the Cleveland Museum of Natural History’s Forensic Entomology web site:

http://www.cmnh.org/site/ResearchandCollections_InvertebrateZoology_Research_ForensicEnt.aspx).

By collecting insects and determining how old they are, investigators can estimate the approximate (or more accurately the minimum) time of death. Blow flies are the most important visitor at carcasses (or human bodies) because of their sensitive sense of smell. They can find bodies/carcasses exposed to nature within minutes or just a few short hours following death and begin to lay eggs immediately. The eggs hatch, and the larvae feed and grow. The trained entomologist is able to age the maggots and therefore judge the approximate time of first egg-laying, thus determining the time between death and body discovery, or postmortem interval. Note that blow flies will not lay eggs on living tissue except under very rare circumstances.

The Cleveland Museum of Natural History acquired a black bear struck by a car in Ashtabula County some 10 years ago. It can not be taxidermied, so the bear will be used as a foresnic wildlife study subject. The specimen will be placed out at an undisclosed (for security purposes) site in Geauga County, Ohio, and left to the insect scavengers who will “recycle” the bear carcass back to nature. At the conclusion of our observations, the bones will be collected and placed in the Museum’s osteology (bone) collection.

Soon after the bear is placed in nature, pigs will be placed out cotangentially for comparative purposes. Because of their percent hair cover on the body, size, and volume of body cavity is similar to humans, swine make fine substitutes for human cadavers during forensic entomology investigations.

We will upload text, photo, and video observations of this decomposition study throughout the summer.


Joe Keiper, Ph.D.
Curator of Invertebrate Zoology
Cleveland Museum of Natural History
16 May 2007