This is Scientific Americans 60 Second Science.

I'm Marissa Shea.

One of the delights of summer is watching monarch butterflies dancing through the air,

but it's becoming harder to see them in certain locales.

In some places, the population has dropped by as much as 90 percent, and climate change may

make life even more challenging for these charismatic insects.

That's because higher carbon dioxide levels can lower the amount of toxins in milkweed,

the monarch caterpillars food.

The caterpillars use those toxins to protect themselves

from a deadly parasite that produces spores. When the caterpillars are really

small, those spores get into the monarch's gut and they break apart and

they start drilling holes in the gut lining and

reproducing and just doing nasty parasite things that are bad for the monarchs.

Leslie Decker, an ecologist at Stanford University.

Decker and her colleagues raised hundreds of monarchs. They fed half the Caterpillar's milkweed grown at current CO2 levels.

The other half got milkweed grown at nearly double those CO2 levels.

What we found is that elevated CO2

changes the medicinal quality of the milkweed

in a way that makes monarchs sicker.

They're less able to tolerate their pathogen,

so the parasite becomes more hurtful to them and it also reduces their

overall lifespan when they're infected in comparison to uninfected monarchs.

...