Hi Mary, 

Yes, it does appear to be woolly adelgids - a major pest of hemlocks in Maryland. It looks like you can treat your tree and should recover. Removal may not be necessary since smaller infestations can be treated by spraying an insecticide. You can use this tool to find a local licensed arborist who is certified to apply insecticide to the affected trees.

Trees in the hemlock family are part of the Pinus genus (Pine tree family), which are considered 'keystone' species - they are host plants that feed the young caterpillars of approximately 90% of butterflies and moths (Lepidoptera). In fact, your hemlocks are host to 200 species of caterpillars! For this reason, management of the pest is recommended rather than removal.

You can check out the National Wildlife Federation's (NWF) full list of keystone species for our ecoregion here, along with the number of caterpillars it supports.

Jamie