Ant Junit tests are running much slower via ant than via IDE - what to look at?

<junit fork="yes" forkmode="once" printsummary="off">
        <classpath refid="test.classpath"/>
        <formatter type="brief" usefile="false"/>
        <batchtest todir="${test.results.dir}/xml">
            <formatter type="xml"/>
            <fileset dir="src" includes="**/*Test.java" />
        </batchtest>
    </junit>

todir="${test.results.dir}/xml"