Which special characters need escaping in a solr query?

You need to use the lucene solr syntax for regexes: http://lucene.apache.org/core/6_5_1/queryparser/org/apache/lucene/queryparser/classic/package-summary.html#Escaping_Special_Characters

It might be a good idea looking at http://lucene.apache.org/solr/4_2_1/solr-solrj/org/apache/solr/client/solrj/util/ClientUtils.html#escapeQueryChars(java.lang.String)