Subject: Caterpillar ?
Geographic location of the bug: Uk Britain
Time: 07:42 AM EDT
Your letter to the bugman: Hi, I found this on my decking and was surprised how aggressive and fast it was, could you identify it please
How you want your letter signed: Mark morgan
This is an Elephant Hawkmoth Caterpillar, Deilephila elpenor, and according to Wildlife Insight: “The Elephant Hawk-moth caterpillar grows to 85mm in length and is one of the largest and most distinctive caterpillars to be found in the British Isles.
It is also the most frequently seen hawk-moth caterpillar, often found feeding and wandering in search for somewhere to pupate in gardens.
The species is named after the caterpillars resemblance to an elephants trunk.
When retracted the caterpillars head recoils giving the impression of a much larger head. The two large ‘eye-like’ markings behind the head also suggest a much larger animal, appearing startling to predators.” The aggression you mention is an act. Often Hornworms in the family Sphingidae will thrash about hoping to startle a predator into perceiving a threat.