...Or at least a couple to choose from. One of the great difficulties of searching for an insect with a particular description is the sheer number of the creatures that exist. Combine that with the fact that new species are always being discovered and the taxonomic system is in a state of flux, and being sure that you have exhausted all plausible matches is nearly impossible. Any characterization of a Suborder or Family is a description of the traits possessed by most submembers, but there are always exceptions. Sadly, there is really no practical way to incorporate these exceptions into the search, so if any of them is a possible Gregor Samsa, it will fall through the cracks.
That said, the hierarchical taxonomic system allows for the dismissal of many subcatagories at once. First, it is helpful to narrow down the search field to a single Order, as that alone will knock hundreds of thousands of species off the list. Two Orders have the necessary elytra: Hemiptera ("true bugs") and Coleoptera (beetles). One distinguishing characteristic of so-called true bugs is that their mandibles have developed into proboscises. At first this was a feature that seemed to have potential; when Gregor first eats in his new form, he is described as "sucking greedily on the cheese." What better to suck up food with than a proboscis? However, it is directly stated that he has "strong jaws," which he uses to turn the key to his room. Neither Coleoptera nor Hemiptera possess both mandibles and proboscises (bees, incidentally, do have both, but Gregor is certainly no bee). I feel that the evidence is significantly more compelling for Gregor having mandibles, and that the description of him "sucking" the food is meant more to relate the strangeness of eating in a new way.
So, Gregor is a beetle. But what kind? there are over 350,000 species of Coleoptera. Time to return to the attributes list. The beetle must have a relatively broad, rounded body. It must feed on decomposing organic matter. It must be brown. It must be flightless.
Within the Order of Coleoptera, some Families can be quickly eliminated. For instance, the family Elateridea (click beetles) have a mechanism for righting themselves if flipped onto their backs. Kafka describes Gregor having much difficulty turning over from his supine position in bed. Weevils (Superfamily Curculionoidea) have characteristic long snouts, which nothing in the text suggests. More important, though, is which groups do fit the qualifications. Once all the factors are added in, the best match is the Superfamily Scarabaeoidea (the only Superfamily in the Infraorder Scarabaeiformia). Within this Superfamily are contained all the necessary traits. Now the task is to find which subcatagories possess them all, without additional prohibitive traits.
By process of elimination, most of the Families can be discounted. Passalidae have the wrong diet, while Lucanidae (stag beetles) have distinctive horns.* Many of the families have long hairs or are capable of flight. Of the Families within Scarabaeoidea, only two have all the requisite characteristics and nothing prohibitive: Scarabaeidae (scarab beetles) and Geotrupidae (ground-boring dung beetles). Either of these could be Gregor's Family.
Now, if the idea of taxonomic Family doesn't quite fill you with warm fuzzies, consider the fact that from a pool of over 350,000 possibilities, the candidates have been narrowed to a scant 30,600 and dropping fast. While Geotrupidae is a relatively small Family (containing only about 600 species), Scarabaeidae is quite large, incorporating nine Subfamilies. Luckily, of those only one matches Gregor's description, that being the Subfamily Aphodiinae. Within Aphodiinae, few species have the correct diet. The ones who do are mainly found in the Tribe Aegialiini. Within Geotrupidae, information is hard to find. However, the Genus Thorectes fits all necessary qualifications.
And that, I think, is as close to an answer as it is currently possible to get. I propose that Gregor Samsa is a scarab beetle of the Tribe Aegialiini, or a ground-boring dung beetle of the Subfamily Thorectes. At last, a (more specific) identity for Gregor.
For me, possibly the most delightful part of this conclusion is that the character of the cleaning lady- portrayed as vulgar and uneducated- came closer to the truth than any of the text's many interpreters.
*Note: Many female stag beetles do not have horns. However, in my research I am making the assumption that Gregor's human sex translates to his insect sex.