Finishing up your holiday gift-buying this week? If your recipient list includes a lady firefly, we’ve got the perfect idea: a gooey bundle of protein-packed sperm. Researchers, writing in the journal Scientific Reports, say these "nuptial gifts" from male fireflies to their mates contain an astonishing array of fertility-promoting nutrients.

Corresponding author Sara Lewis specializes in sexual selection in insects. Lewis and her colleagues at Tufts University have been studying firefly sex for years, and they’re still not sick of it—nor are the fireflies, apparently. “I think it’s safe to say that adult fireflies are obsessed with sex,” she said in a statement. She and her team have identified some of the crucial factors in firefly courtship, but the firefly’s gift has remained something of a black box.

Terry Priest via Flickr Creative Commons // CC BY-SA 2.0

 
Nuptial gifts are a normal part of the mating game for many insect species. Male bugs use them as an enticement and as a way of boosting the odds that their genetic material will make it to the next round. The substance of these gifts varies quite a bit, from decorated crickets’ “gummy bears” to male mantises’ ultimate sacrifice of their own bodies.

To peek inside the firefly’s gift, the research team sent the little packages through a gauntlet of genetic, proteomic, and metabolomic tests, trying to create an ultimate ingredient list.

That list proved to be long, including more than 200 different proteins. Some of those compounds make up the physical stuff of the capsule; some help break it down and become useful once it enters the female firefly’s body. Others prompt her body to produce more eggs, hold on to sperm, or increase the sperm’s efficacy. The gift also contains a nasty-tasting toxin called lucibufagin, which has previously been shown to help protect firefly eggs from predators. It is, in short, the total nuptial package.

And it works well. The research team found that lady fireflies who consumed nuptial gifts produce more eggs over their lifetimes and even live longer, while males who give larger gifts tend to have more kids.

Co-first author Nooria Al-Wathiqui calls the little bundles “complex, elegant structures” and says they’re produced by “a bevy of male glands. In fact, if you look inside a male firefly, you’ll find them jam-packed with gift-making machinery.”