Beetle Juice and Black Bass

Join Our Community of Science Lovers!

Image: after Eisner et al., PNAS

The tiny whirligig beetle has an effective defense against the fish it regularly encounters in ponds and slow streams: from two glands opening at the tip of its stomach, this surface swimmer secretes a combination of chemicals, including gyrinidal, that apparently make it taste bad. New research shows that largemouth black bass in particular will either avoid this beetle juice or try to rinse it off before eating a whirligig. Cornell University scientists Thomas Eisner and Daniel Aneshansley describe the finding in the October 10th issue of the Proceedings of the National Academy of Sciences.

Eisner and Aneshansley conducted a number of experiments on the beetles and bass they collected from ponds near Cornell. When they fed the bass both beetles and their larvae, mealworms, they discovered quickly that the secretion-free mealworms were clearly preferred (see chart). Whereas the bass ate all of the mealworms, they ignored some 80 percent of the beetles. The three that were eaten--all by one fish--were flushed first: the bass went through an elaborate process of spitting the bug out and reingesting it repeatedly. Other bass spit out for good the whirligigs they flushed, and in all cases the beetles were no worse for the wear.

On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

In another experiment, Eisner and Aneshansley coated the mealworms with the beetle juice and found the larvae were also heavily flushed, although eventually eaten. The mealworms' ultimate fates, the authors suggest, is because the secretion can be completely rinsed off. The beetles, in contrast, emit this chemical slowly and steadily. The researchers further demonstrated that the amount of flushing the fish did was dependent on the dose of the secretion--and that the fishes' tolerance for it rose with their hunger.

It’s Time to Stand Up for Science

If you enjoyed this article, I’d like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.

I’ve been a Scientific American subscriber since I was 12 years old, and it helped shape the way I look at the world. SciAm always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does that for you, too.

If you subscribe to Scientific American, you help ensure that our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten labs across the U.S.; and that we support both budding and working scientists at a time when the value of science itself too often goes unrecognized.

In return, you get essential news, captivating podcasts, brilliant infographics, can't-miss newsletters, must-watch videos, challenging games, and the science world's best writing and reporting. You can even gift someone a subscription.

There has never been a more important time for us to stand up and show why science matters. I hope you’ll support us in that mission.

Thank you,

David M. Ewalt, Editor in Chief, Scientific American