Re: What are the ants on my cornflowers doing?

Your previous answer was correct.
 Some plants leak sap especially if nipped, sap is sweet so they may be 
sucking minute bits of sap from the plant. They may be scraping small 
amounts of organic matter off the surface. The worker ants are scavengers 
and collect seeds, nectar, even dead insects as well to take back to the 
next. They also prey on greenfly, blackfly and other
small insects.
I did a search on them and found that they also might be tending to aphids 
or defending a possible aphid farm from other insects look below to see if 
there are any aphids on the plants. 
Here are some more sites for information.  Enjoy!



http://www.tameside.gov.uk/corpgen1/gardenants.htm
 

http://www.myrmecology.org/javai
ndex.htm

http://www.exeter.gov.uk/services/departments/environmentalhealth/pest/