This insect looks like a hairy striped caterpiller with horns!
THAT'S BECAUSE IT IS A HAIRY STRIPED CATERPILLAR WITH HORNS.
VAPOURER MOTH CATERPILLAR.
MORE INFORMATION THAN YOU PROBABLY WANT HERE:-
That is one really interesting caterpillar. Thank you. It will encourage me to diversify my plants, if they become a problem. It's nice to be forewarned that they can irritate the skin if you touch them.