冰虫是指Mesenchytraeus属的环节动物的总称，生活于北极地区的冰层中。

Mesenchytraeus solifugus是最早发现的种类，于1887年在阿拉斯加发现。是地球上极少数能在摄氏0度以下仍能生存的生物。冰虫的酶在接近零度左右仍有活力；但温度若超过5度，酶便会消化其细胞膜，把冰虫本身给溶化。冰虫可达约数公分长，体色有黑、蓝、白等。在约清晨及傍晚时会接近冰层表面。以雪水藻类和花粉为食。

目前仍不清楚冰虫如何在坚硬的冰层中创建信道。一些科学家认为冰虫是以冰床中的超细微缝隙来旅行；一些人则相信冰虫可以分泌某种化学物质来溶解冰层。

Ice worms are annelids of the genus Mesenchytraeus. They are the only annelid worms known to spend their entire lives in glacial ice. They include M. solifugus, M. harrimani, M. kuril, M. maculatus and M. obscurus.

The first ice worms species were discovered in North America in 1887 in Alaska, on the Muir Glacier. These glacier ice worms can be found on glaciers in Alaska, Washington, Oregon and British Columbia. They have not been found in other glaciated regions of the world. The specific name solifugus is Latin for "sun-avoiding," as ice worms retreat underneath the ice before dawn. Enzymes in ice worms have very low optimal temperatures, and can be denatured at even a few degrees above 0 °C (32 °F). When ice worms are exposed to temperatures as high as 5 °C (41 °F), their membrane structures disassociate and fall apart (i.e., "melt") causing the worm itself to "liquefy." Ice worms are several centimeters long, and can be black, blue, or white. They come to the surface of the glaciers in the evening and morning. On Suiattle Glacier in the North Cascades, population counts indicated over 7 billion ice worms.