marigold caterpillars

Many of our marigolds have small green caterpillars in the flowers. The flowers then get malformed. Does it help if I pick off those flower heads, and can I just drop them on the soil (as I have been doing) or do I have to compost them properly?
What are the caterpillars called? And could the trouble be caused by this year's terrible drought? I've grown marigolds for decades, mostly in the same place, and never had trouble before.

 

Hi

they are a moth I get them on some of my plants are your marigolds "Callendula" variety as my French dont get touched by caterpillars

if and when you pick the flowers off you need to crush them underfoot otherwise the caterpillars may crawl to the next available plant

 

Hens will eat Callendula/Pot Marrigold flowers and doing so will increase the colour of egg yolks, any attached caterpillars will be tasty treats.

 

Thanks Spruce, yes they are calendula. I'll try and crush them, in friendship of course!
And Scrungee, I dry the petals for lutein, which is very good for my eyes and skin. So luckily I haven't got hens to eat them ...