Homosexually Humping Corpse-Eating Beetles Here For A Good Time, Not A Long Time

Heat Stress Increases Same-Sex Mounting in Burying Beetles

New research indicates that male burying beetles (Nicrophorus vespilloides) mount other males more frequently when exposed to heat stress. While scientists previously hypothesized that heat might disrupt the chemical signals beetles use to identify mates, the study revealed that same-sex mounting is a common occurrence even under normal environmental conditions.

The findings, presented at the Society for Experimental Biology conference in Florence, Italy, highlight the complex ways climate change may influence the social behaviors of ectothermic insects. Solène Morelle, a PhD student at the University of St Andrews in the United Kingdom, led the investigation into how rising temperatures affect the beetles’ ability to communicate and reproduce.

Chemical Communication and the Climate Trade-Off

Burying beetles rely on a thin layer of waxy substances on their exoskeletons called cuticular hydrocarbons (CHCs) to navigate their environment. These molecules serve two primary, and potentially conflicting, functions: they prevent the insects from dehydrating in hot, dry habitats and act as chemical signals for communication.

According to Morelle, there is evidence of a trade-off between the waterproofing and signaling roles of these hydrocarbons. Longer-chain CHCs are more effective at preventing water loss because they are less likely to evaporate, while shorter-chain CHCs are more volatile, making them easier for other beetles to detect.

In a warming climate, beetles may shift their CHC profiles toward longer chains to prevent dehydration. Researchers suspect this shift could make the chemical signals used to distinguish between sexes or identify rivals less effective. If a beetle cannot accurately identify a potential mate, it may lead to errors in reproductive behavior.

Experimental Results: Heat vs. Normal Conditions

To test the impact of heat on behavior, the research team conducted an experiment comparing burying beetles kept in controlled conditions at 68 degrees Fahrenheit (20°C) against a group subjected to a simulated three-day heatwave at 79 degrees Fahrenheit (26°C).

Morelle observed the frequency and duration of mounting encounters among the beetles. While she hypothesized that heat would increase sex recognition errors—leading to more same-sex mounting—the results provided an unexpected baseline.

I was surprised to find out how much same-sex mounting the beetles showed, even under normal conditions, Morelle stated. While the heatwave did lead to a further increase in reciprocal mounting among males, the fact that the behavior occurs regularly when temperatures are mild suggests it may not be a simple mistake.

Implications for Parental Success and Survival

Burying beetles are known for their involved parental care, which includes burying small carcasses—such as mice and birds—to serve as a nursery for their larvae. This process requires significant coordination between mates, including protecting the nest and driving away competitors.

Because effective communication is essential for these tasks, researchers are concerned that heat-induced chemical changes could have broader consequences. If a beetle fails to distinguish between a cooperative partner and an intruder, the resulting confusion could threaten the survival of an entire brood.

However, researchers note that the physiological cost of a single unsuccessful mating attempt is likely low. The physiological cost of a single unsuccessful mating attempt probably isn’t very high on its own and does not outweigh the risk of losing a chance to mate with a female, Morelle noted.

Understanding the “Why” Behind the Behavior

Currently, it remains unclear why male burying beetles engage in same-sex mounting so frequently. Beyond potential errors in sex recognition, such behavior can also occur during social conflicts, competition, or periods of high activity. The research team is continuing to analyze their chemical data, using gas chromatography-mass spectrometry to identify the specific compounds involved. As climate change continues to push ectotherms toward their physiological limits, understanding these subtle shifts in social behavior is becoming increasingly critical to predicting the long-term reproductive success of these species.