A strain of cockroaches in Europe has evolved to evade sugar traps used to eradicate them, scientists said in a study published on Thursday.
A team from North Carolina State University found that the newly improved cockroaches had a "reorganized" sense of taste, making them perceive glucose used to coat poisoned bait as bitter rather than as sweet.
The American scientists tested their theory by giving the super-bugs a choice of jam or peanut butter, then analyzed their taste receptors, which are similar to human taste buds.
"Cockroaches are highly adaptive, and they’re doing pretty well in the arms race with us," said North Carolina State University entomologist Jules Silverman.
The same team first noticed the change 20 years ago when some pest controllers were failing to get rid of cockroaches because the insects refused to eat the bait.
More from GlobalPost: Cockroaches have ninja-like skills to make their escape
Dr. Coby Schal also explained that the newly published study had revealed the "neural mechanism" behind the refusal and why the cockroaches now think sweet is bitter.
But the phenomenon doesn't occur in all varieties of cockroaches. The glucose-hating bugs were collected in Puerto Rico as well as descendants of the Florida insects, and the research focused on the German cockroach, a version of the bug that is much smaller than the better known American roach. Other types of cockroaches with the finicky eating habit are from Southern California, Cincinnati, Indiana, South Korea and Russia.
Scientists are now looking for other kinds of cockroaches that show aversion to glucose.