Later arrivers...

19 July 2007: Upper left, Stearibia nigriceps, a piophild fly; Upper right, Leptocera sp., a minute dung fly of the family Sphaeroceridae; Lower left, Nicrobia violaceae, a beetle of the family Cleridae; Lower right, another fly of the family Piophilidae, Prochyliza.

The flies and beetle illustrated above are common on both the pig and the bear carcass. They illustrate nicely the concept of change through time as they come after the initial wave of blow flies and house flies. They are adapted to the drying conditions encountered on an aging carcass, and take advantage of the areas of carcasses touching the ground. Here, it is moist, dark, and protected.

In terms of our use for determining a postmortem interval, these species are not as useful as blow flies. But, they their presence or absence can be useful. They indicate a change in the carcass, and are part of the insect succession.

All four species above are generalized scavengers of decaying animal tissue in the larval stage. The adults seen above really are there to mate and lay eggs. The adults do little if anything to aid decomposition directly.

The Ecological Players in the Decompositonal Game

15 July 2007: Upper left, Phormia regina, the black blow fly; Upper right, Lucilia illustris, a green bottle fly; Lower left, Fannia canicularis, the lesser house fly; Lower right, Sarcophaga sp., a flesh fly.

OK, not much has been happening on the pig or bear carcasses. So we shall take a detailed look at some of the insects obtained during the course of this investigation.

The flies illustrated above are some of our most informative and/or interesting flies on the decomposing bear and pig. The two above represent our predominant blow flies. The green bottle fly (Lucilia illustris) is one of several species of green bottles we encounter regularly on carrion here in northeastern Ohio. It is often the first to arrive, and based on our sweeping of adult flies off the carcasses, larval collections off of the carcasses, larval collections of the wandering masses of maggots, and our rearings, we found that L. illustris was indeed the first arriver.

The black blow fly (Phormia regina) arrived and developed concurrently with L. illustris, but developed a little more slowly. Lucilia flies were only present on the carcass for a short while, followed by numerical domination by the black blow fly.

The lesser house fly (Fannia canicularis) was interesting. Not an early arriver, nor very predictable in its arrival time, it is not a precise predictor of time of death. However, the literature suggests it arrives when fecal material in the guts of the carcasses are exposed. Our observations show that this is not necessarily the only time it arrives and deposits eggs. We found that the adults lay eggs underneath the dry carcasses on the vegetation, and the larvae develop nicely on the blackened, decomposing grasses fouled by mammal decomposition. Further, we obtained eggs, larvae, and pupae of this species when we exposed raw beef.

Lastly, Sarcophaga or flesh flies are often times present in reasonable numbers on carcasses. I reared flesh flies off a dead shrew near this field site recently, and it was the only taxon present on the small carcass. We have so far recovered no individuals from any of our efforts. The lack of flesh flies is both interesting and not easily explained.

Next post, we shall provide information on more fly species taken on our pig and bear carcasses.

A tale of two carcasses...

2 July 2007: We are still keeping an eye on the bear periodically. We lift the legs, head, and torso to accumulate a collection of cryptic beetles and their larvae. This will allow us to document relatively long-term succession of insects on the carcass. During this phase of deep dessication, we collect beetles and sweep for flies approximately weekly.

2 July 2007: The pig, like the bear, is also in the dry phase of decomposition. The underside is still moist, and maggots are present (see below).

2 July 2007: This morning, just a few hours short of exactly 1 week into decomposition, we had a mass exodus of maggots from underneath the carcass. The grasses and weeds obscure the view, but in the photo above you can make out the larvae clearly. The smaller carcass supported fewer numbers than the large bear (a 119 pound difference), but there were thousands of maggots moving into the undergrowth to burrow into the soil for pupariation.

3 July 2007: After the movement of maggots off the body yesterday, little activity is observable.

3 July 2007: The effects of maggot feeding... The larvae consume the carcass down to the bone, exposing the drying internal organs and pave the way for a dry phase of decomposition. This is where beetles, sepsid flies, and piophilid flies become the dominant players.

4 July 2007: We're pretty much in a phase where, like the bear, decomposition will progress very slowly. We'll continue to collect, but not daily. We will collect beetles on our under the carcass and sweep for flies 1-2 times per week. It is very overcast today, and rain appears to be iminent. That being so, we may see a resurgence in fly activity. If it does indeed rain, I'll head out check again today. The moisture will make some of the tissue soft again, and perhaps we'll have a second wave of blow flies. It really depends on how much rain we get, if any...