Blue Jay Emetic Unit

As defined by biologist Lincoln Brower, a "blue jay emetic unit" is the amount of cardiac glycosides (a type of poison found in plants such as milkweeds) that will make one blue jay vomit. Brower determined the exact amount by putting cardiac glycosides into gelatin capsules which he force-fed to blue jays.

The point of this was that various butterflies ate milkweeds and then became poisonous to the blue jays which, in turn, ate them. Knowing the exact amount of poison needed to make a blue jay vomit allowed Brower to rank each butterfly by its number of blue jay emetic units:

The experiments showed that a monarch that has eaten Asclepias humistrata contains enough poison to make approximately eight blue jays vomit; a butterfly reared on Calotropis procera contains 4.8 blue jay emetic units; one that has eaten A. Curassavica, 3.8 units, and one that has eaten Gomphocarpus, .8 unit. In other words, there is a palatibility spectrum, and the most unpalatable butterfly is at least 10 times as emetic as the most palatable one.

Source: Brower LP (Feb 1969). "Ecological Chemistry." Scientific American 220(2): 22-29.

"barfing blue jay" (picture by Lincoln Brower. Source:

     Posted By: Alex - Wed Oct 03, 2018
     Category: Nature | Science | Experiments

Gross if not interesting.
Posted by gary lee ridge on 10/03/18 at 10:13 AM
I thought this was some weird ad for the Toronto Blue Jays. Get you Blue Jays emetic unit today!
Posted by Yudith on 10/03/18 at 08:00 PM
Another chapter of Mother Nature's never ending program of chemical warfare.
Posted by KDP on 10/04/18 at 08:35 AM
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