Public Health

“Ladybugs use a defensive behaviour called ‘reflex bleeding’ when threatened,” explained Sophie Thorogood, technical training manager at Pest-Stop. “This releases a yellowish body fluid, known as hemolymph, which smells unpleasant and can stain fabrics. If you squash them, this fluid will be released.”

The ladybug expresses the hemolymph through the joints in its legs, as a deterrent to any predators. It works thanks to the isopropyl methoxy pyrazine inside the fluid, which gives it its distinctive odor and taste. The smell alone would be a good reason not to squash a ladybug; the bad odor can linger even after wiping away the liquid.

But hemolymph can also cause damage once released. This is because it is also made up of alkaloids that are toxic to many ladybug predators — and can even cause numbness or irritation to some humans.

“It’s better to move them outside and let them be on their way, rather than squish them"

For those who aren’t sensitive or allergic to hemolymph, there are still other negative consequences of squishing ladybugs. The fluid can stain both fabrics and surfaces with its yellow or orange color, causing long-term discoloration that can be hard to remove. Not only is this unsightly, but no one needs reminding of the cute ladybug they killed.