Burmy were once thought to be a pokemon which could not survive winter unless they first evolved, and instead would lay their eggs and wait for a new generation to hatch in the spring. This was not because of cold temperatures, but because wild Burmy make their cloaks from the leaves of deciduous trees, for the needlelike leaves of evergreens make for poor cloak material. Because their cloaks are usually destroyed after a single battle, the second attempt to attack these pokemon would leave them helpless against predators.
Yet Burmy are a remarkably adaptable species, and in the company of trainers, far from their forest homes, they have been observed making cloaks out of sand or even garbage. With the advent of the snowplow, many drivers reported witnessing live Burmy in the vast piles of snow they cleared from Sinnoh's roads, and further investigation revealed that these pokemon were real and survived this season by making cloaks out of snow. However, their snow is packed too tightly to allow easy movement, so Burmy typically hibernate during the winter; if they are forced to move, their cloak will disintegrate without even needing to be scratched.
There are no recorded instances of snow-cloaked Burmy evolving into Wormadam, although this hypothesized snow forme has captured the imagination of artists and scientists alike. They can not become stronger through battle in these cloaks, and feeding them rare candies is impossible, for Burmy refuse to don their cloaks of snow when they have a pokeball to call home.