London design studio Osborne Ross has created a set of six animal-shaped Royal Mail stamps designed to appeal to children (+ slideshow).

Each of the creatures appears to hang or cling onto the envelope, with a koala shown gripping the edge and an orangutan swinging by its arms.

The collection also includes a snake – shown wrapped around a traditional rectangular stamp – bat, chimpanzee and woodpecker.

"The brief from the Royal Mail at the beginning was very open: design something which has never been done before and which will appeal to children," the consultancy's Andrew Ross told Dezeen.

Each animal was first illustrated by the studio before being reworked to conform with Royal Mail's technical requirements, which dictate where a stamp can appear on an envelope and what colours can be used.

Osborne Ross sent several trial variants through the postal system before adjusting the final designs and adding straight edges for perforations into each of the creatures.

"We presented several ideas but this was the one that everyone liked from the very start," added Ross. "We tried variants using people but animals gave more scope in terms of hanging and clinging onto things; they were also inherently cuter."

It's not the first time Osborne Ross has partnered with Royal Mail, previously designing a collection of stamps that showed endangered insects and a Christmas set featuring stained glass windows created by William Morris.

The postal service collaborated with Hat Trick Design in 2012 on stamps that commemorated the London Olympics by featuring architecture from around the capital.

Dutch national delivery company PostNL also has a history of commissioning striking stamp sets, working with Tord Boontje last year on a collection of festive designs featuring woodland animals.