Mystery bug on a Pear tree

Mystery bug on a Pear tree

Observation - Mystery bug on a Pear tree. Description: There were several of these small bugs on a Pear tree in a wildlife patch on the local allotment. They are only a bit larger than the ants that were also on the tree. They varied a bit in coloration with some being a bit darker than others and later in th

There were several of these small bugs on a Pear tree in a wildlife patch on the local allotment. They are only a bit larger than the ants that were also on the tree. They varied a bit in coloration with some being a bit darker than others and later in the day they disappeared.

We have no idea what they are, or even what order they might belong to, we wondered if they might be some kind of wingless moth?