I got into work early this morning. At the doorway to the bathroom I frequent, I beheld an amazing sight. There was a sizeable, light-coloured insect in a state of disassemblage on the floor in front of the door. Picking through the wreckage was a slightly smaller dark insect with a chitanous carapace.
I wanted to stay and watch, but I also had to use the bathroom. After I finished my business, they were still right there on the floor. I hopped back into my office (next to the bathrooms), grabbed a piece of paper, and scooped them up for closer examination on my desk.
Of course, once they were placed on the desk, the still-living insect bolted for the nearest cover (a Compaq Presario v5000). I played hide and seek with it for about 6 minutes, but quickly tired of its survival instincts. What I wanted to see was its gluttony so that I could capture the feeding on camera, so I proferred the remnants of its meal, still on the paper, to the scurrier but to little avail.
Clearly it was not comfortable eating in plain sight where it preceived imminent danger. So I relocated them to the floor under my desk. Under relatively darker evirons, the black bug was content to return to feeding. I filmed it with a point-and-shoot camera (Casio Exilim Z55) that was woefully ill-equipped to handle dark and close-up work. Nonetheless, I faithfully captured the moment the best I could, partially lying on the floor of my room while some automated processes were running.
Fig. 1: Video of Feeding
Naturally, the mystery of the identities of the insects began to draw my attention after the novelty of watching one insect dig through the innards of another, less fortunate insect lost its appeal. For posterity, I took a few snapshots. Again, it must be reiterated that my camera is not built for close-up work, so sadly, the quality leaves a lot to be desired.

Fig. 2: Feeding in the Dark

Fig. 3: Really getting in there

Fig. 4: Nom nom nom nom
During the course of the composition of this post, I did some research into the insects I observed. The living one was easy enough to identify, as I had a specimen that had been stepped on, but remained largely intact (COD: thoracic rupture). It looked like a black beetle that lived on the ground; this was verified by a quick Google Image Search for "Black Ground Beetle".
The edible one proved to be more difficult, owing to several of its body parts being detached and likely missing. Its most striking feature, apart from its ability to separate into pieces, was the pair of filament-like structures protuding from its abdomen. Such a feature is fairly rare in the insect world, allowing me to rule out about 90% of them right away. From this point, I just had to look up pictures for known insects with tail-like structures.
At first, it seemed like Bristletails fit the bill, but closer inspection revealed that bristletails did not have the same kind of long legs seen in the photos. I've finally settled on Mayfly. Mayflies have the filamentous tails and long-ish legs seen in the photographs.
The ground beetle was likely scavenging the remains of a dead mayfly, as beetles generally have a tough time tackling airborne prey. Adult mayflies live only a couple of days, devoting all that time to reproduction. The wings were likely bitten off at the first opportunity to reduce dragging weight.
