As the saying goes, one man’s meat is another man’s poison. Whereas the smell of decomposing flesh would put a human off the idea of sex, if you’re a young virgin female hide beetle, then it’s “OOH BABY!” But it’s not just the smell of cadaver that has the lady beetles reeling, it’s the smell of sex in the air.
Chemical compounds known as pheromones send airborne messages between members of the same species, conveying information ranging from “This way to food” to “I’m fertile, frisky, and ready for action!”
When virgin female hide beetles get a whiff of cadaver mixed with male sex pheromones, then it’s time to cue the Barry White. Neither scent alone does it for the females, but the combination ensures that there is both a male to mate with and a food supply for her larvae, increasing the chance of reproductive success.
To find out if virgin female hide beetles are attracted to this combination of smells, and during which stage of decomposition this occurs, a team of researchers, led by Christian von Hoermann from Ulm University, Germany, filled olfactometers with different volatile scents and recorded which scents the virgin female hide beetles were attracted to. The scents used were pig cadaver (collected at different stages of decay), male pheromone gland extract, synthetic pheromones, and a control, pentane (an organic solvent used to extract the other odors). Piglet cadavers were used because they resemble human torsos in hair coverage, the ratio of fat to muscle, biochemistry and physiology, and likely have an odor-profile similar to the volatile compounds found in a human cadaver.
The females ignored both the control and the synthetic pheromone. They also ignored everything apart from the smell of piglet in the dry remains stage, so long as it was accompanied by male pheromones. (Because nothing says baby-makin’ like desiccated bacon, amiright?)
How and when the first receptive females appear on a carcass, as well as the developmental stages of their larvae, are important components of determining the time since death.
Anyone who has watched CSI knows that decomposition of a cadaver is accompanied by a series of various insect species, all which have evolved preferences for different stages of decomposition. During the first stage of decomposition, the fresh stage, the first insects to arrive are blow flies and flesh flies, which can arrive within minutes of death and whose eggs and larvae need moist tissue for successful development. During the next stage, the bloated stage, the cadaver is teeming with masses of feeding maggots. In the post-bloating stage, rove beetles and clown beetles arrive, who eat the fly larvae.
This little piggy never made it to market. Source: Wikimedia Commons
By now, the cadaver is ripe for dermestid beetles, such as the hide beetle, because they feed on the remaining cadaver skin and ligaments. More than 3,000 hide beetles have been recorded on a single cadaver, which can be completely stripped to the bones by their corpse-snacking larvae. These larvae feed and remain on the dried-out cadaver skin after most of the adults have left following they’ve had their fill of food and sex.
During the last two stages, the advanced decay stage and the dry-remains stage, checkered beetles, skin beetles, and scarab beetles are present. The life cycle and sequence of arrival for these species is so predictable, that forensic scientists use their presence to estimate the time of death.
Although cadaver odor alone is enough to attract the freshly emerged male hide beetles, approximately 9 days after death, the smell of bacon alone isn’t enough to attract the 2 to 3 week old virgin females, who also want the promise of sex. Evolution appears to have ensured that female hide beetles only respond to the smell of a mate or a larval food source when the other is also present, indicating the perfect spot for feeding, mating and egg laying, and increasing the chance of survival for their offspring.
von Hoermann, C., Ruther, J. & Ayasse, M. (2012) The attraction of virgin female hide beetles (Dermestes maculatus) to cadavers by a combination of decomposition odour and male sex pheromones. Frontiers in Zoology (in press).