Citizen science?

As I walked along a green lane decorated on either side by an abundance of  late spring flowers I noticed the arrival of cuckoo spit, those frothy dollops that cling to leaves and stems. It's created by baby froghoppers (tiny bugs) that ingest the plant sap and foam it up to conceal themselves inside the bubbly blobs. Nothing to do with actual cuckoos, it's just that the  stuff  appears round about the time that the birds [used to] "sing night and day". 

Red campion seemed to be especially  popular with spittlebugs (alternative name) - there were  gobbets of goo hanging all over it. Except, not quite: I noticed that the froth was all parked on the leaf bracts and not on the flowers. It figures, because there's no sap in the petals.

Then I noticed something else. Even though there were  campion and  foxgloves growing right next to each other, there was no cuckoo spit at all on the foxgloves. There were many many foxgloves and I inspected all most of them as I ambled by. Nope, no cuckoo spit. SO,  the adult leafhopper must "know" that foxglove sap is toxic and would kill the babies if they ingested it to make foam. So they don't lay their eggs on it. Isn't that amazing? 
(Despite scouring the internet for confirmation of this I've found no reference to froghoppers avoiding foxgloves. Maybe I've discovered something new to science?)

More about froghoppers