diff --git a/src/pyobo/sources/mirbase.py b/src/pyobo/sources/mirbase.py
index 52c43fec..45233568 100644
--- a/src/pyobo/sources/mirbase.py
+++ b/src/pyobo/sources/mirbase.py
@@ -50,7 +50,7 @@ def get_obo(force: bool = False) -> Obo:
 def get_terms(version: str, force: bool = False) -> List[Term]:
     """Parse miRNA data from filepath and convert it to dictionary."""
     url = f"{BASE_URL}/{version}/miRNA.dat.gz"
-    definitions_path = ensure_path(PREFIX, url=url, version=version, force=force)
+    definitions_path = ensure_path(PREFIX, url=url, version=version, force=force, verify=False)
 
     file_handle = (
         gzip.open(definitions_path, "rt")
@@ -63,13 +63,21 @@ def get_terms(version: str, force: bool = False) -> List[Term]:
 
 def _prepare_organisms(version: str, force: bool = False):
     url = f"{BASE_URL}/{version}/organisms.txt.gz"
-    df = ensure_df(PREFIX, url=url, sep="\t", dtype={"#NCBI-taxid": str}, version=version)
+    df = ensure_df(
+        PREFIX,
+        url=url,
+        sep="\t",
+        dtype={"#NCBI-taxid": str},
+        version=version,
+        verify=False,
+        force=force,
+    )
     return {division: (taxonomy_id, name) for _, division, name, _tree, taxonomy_id in df.values}
 
 
 def _prepare_aliases(version: str, force: bool = False) -> Mapping[str, List[str]]:
     url = f"{BASE_URL}/{version}/aliases.txt.gz"
-    df = ensure_df(PREFIX, url=url, sep="\t", version=version)
+    df = ensure_df(PREFIX, url=url, sep="\t", version=version, verify=False, force=force)
     return {
         mirbase_id: [s.strip() for s in synonyms.split(";") if s and s.strip()]
         for mirbase_id, synonyms in df.values
diff --git a/src/pyobo/sources/pfam.py b/src/pyobo/sources/pfam.py
index 5ca2ba44..4df02096 100644
--- a/src/pyobo/sources/pfam.py
+++ b/src/pyobo/sources/pfam.py
@@ -35,6 +35,7 @@ def get_pfam_clan_df(version: str, force: bool = False) -> pd.DataFrame:
         version=version,
         dtype=str,
         force=force,
+        backend="urllib",
     )
 
 
diff --git a/src/pyobo/sources/rhea.py b/src/pyobo/sources/rhea.py
index f7c94993..d680d395 100644
--- a/src/pyobo/sources/rhea.py
+++ b/src/pyobo/sources/rhea.py
@@ -41,6 +41,22 @@ def get_obo(force: bool = False) -> Obo:
 
 def iter_terms(version: str, force: bool = False) -> Iterable[Term]:
     """Iterate over terms in Rhea."""
+    url = "ftp://ftp.expasy.org/databases/rhea/rdf/rhea.rdf.gz"
+    graph = pystow.ensure_rdf(
+        "pyobo", "raw", PREFIX, version, url=url, force=force, parse_kwargs=dict(format="xml")
+    )
+    result = graph.query(
+        """
+    PREFIX rh:<http://rdf.rhea-db.org/>
+    SELECT ?reaction ?reactionId ?reactionLabel WHERE {
+      ?reaction rdfs:subClassOf rh:Reaction .
+      ?reaction rh:id ?reactionId .
+      ?reaction rdfs:label ?reactionLabel .
+    }
+    """
+    )
+    names = {str(identifier): name for _, identifier, name in result}
+
     terms = {}
 
     directions = ensure_df(
@@ -50,10 +66,12 @@ def iter_terms(version: str, force: bool = False) -> Iterable[Term]:
         force=force,
     )
     for master, lr, rl, bi in directions.values:
-        terms[master] = Term(reference=Reference(PREFIX, master))
-        terms[lr] = Term(reference=Reference(PREFIX, lr))
-        terms[rl] = Term(reference=Reference(PREFIX, rl))
-        terms[bi] = Term(reference=Reference(PREFIX, bi))
+        terms[master] = Term(
+            reference=Reference(prefix=PREFIX, identifier=master, name=names.get(master))
+        )
+        terms[lr] = Term(reference=Reference(prefix=PREFIX, identifier=lr, name=names.get(lr)))
+        terms[rl] = Term(reference=Reference(prefix=PREFIX, identifier=rl, name=names.get(rl)))
+        terms[bi] = Term(reference=Reference(prefix=PREFIX, identifier=bi, name=names.get(bi)))
 
         terms[master].append_relationship(has_left_to_right_reaction, terms[lr])
         terms[master].append_relationship(has_right_to_left_reaction, terms[rl])
@@ -97,33 +115,11 @@ def iter_terms(version: str, force: bool = False) -> Iterable[Term]:
                     xref_id,
                 )
                 continue
-            terms[rhea_id].append_xref(Reference(xref_prefix, xref_id))
+            terms[rhea_id].append_xref(Reference(prefix=xref_prefix, identifier=xref_id))
 
     # TODO are EC codes equivalent?
     # TODO uniprot enabled by (RO:0002333)
     # TODO names?
-
-    url = "ftp://ftp.expasy.org/databases/rhea/rdf/rhea.rdf.gz"
-    graph = pystow.ensure_rdf(
-        "pyobo", "raw", PREFIX, version, url=url, force=force, parse_kwargs=dict(format="xml")
-    )
-    result = graph.query(
-        """
-    PREFIX rh:<http://rdf.rhea-db.org/>
-    SELECT ?reaction ?reactionId ?reactionLabel WHERE {
-      ?reaction rdfs:subClassOf rh:Reaction .
-      ?reaction rh:id ?reactionId .
-      ?reaction rdfs:label ?reactionLabel .
-    }
-    """
-    )
-    for _, identifier, name in result:
-        identifier = str(identifier)
-        if identifier not in terms:
-            logger.debug("isolated element in rdf: rhea:%s ! %s", identifier, name)
-            continue
-        terms[identifier].reference.name = name
-
     # TODO participants?
 
     yield from terms.values()
diff --git a/src/pyobo/struct/struct.py b/src/pyobo/struct/struct.py
index f73e5989..54281831 100644
--- a/src/pyobo/struct/struct.py
+++ b/src/pyobo/struct/struct.py
@@ -172,7 +172,7 @@ def _ensure_ref(reference: ReferenceHint) -> Reference:
             raise ValueError
         return _rv
     if isinstance(reference, tuple):
-        return Reference(*reference)
+        return Reference(prefix=reference[0], identifier=reference[1])
     if isinstance(reference, Reference):
         return reference
     raise TypeError
diff --git a/src/pyobo/utils/io.py b/src/pyobo/utils/io.py
index 414b5f4e..d9e0f1d5 100644
--- a/src/pyobo/utils/io.py
+++ b/src/pyobo/utils/io.py
@@ -13,6 +13,7 @@
 from typing import Dict, Iterable, List, Mapping, Optional, Set, Tuple, TypeVar, Union
 from xml.etree.ElementTree import Element
 
+import pandas as pd
 from lxml import etree
 from tqdm.auto import tqdm
 
@@ -108,7 +109,8 @@ def multisetdict(pairs: Iterable[Tuple[X, Y]]) -> Dict[X, Set[Y]]:
     """Accumulate a multisetdict from a list of pairs."""
     rv = defaultdict(set)
     for key, value in pairs:
-        rv[key].add(value)
+        if pd.notna(value):
+            rv[key].add(value)
     return dict(rv)
 
 
diff --git a/src/pyobo/utils/path.py b/src/pyobo/utils/path.py
index b4f30515..b5e27971 100644
--- a/src/pyobo/utils/path.py
+++ b/src/pyobo/utils/path.py
@@ -4,9 +4,10 @@
 
 import logging
 from pathlib import Path
-from typing import Callable, Optional, Union
+from typing import Any, Callable, Dict, Literal, Optional, Union
 
 import pandas as pd
+import requests_ftp
 from pystow.utils import download, name_from_url, read_tarfile_csv
 
 from .misc import cleanup_version
@@ -26,6 +27,8 @@
 
 VersionHint = Union[None, str, Callable[[], str]]
 
+requests_ftp.monkeypatch_session()
+
 
 def prefix_directory_join(
     prefix: str,
@@ -62,6 +65,8 @@ def ensure_path(
     name: Optional[str] = None,
     force: bool = False,
     error_on_missing: bool = False,
+    backend: Literal["requests", "urllib"] = "urllib",
+    verify: bool = True,
 ) -> str:
     """Download a file if it doesn't exist."""
     if name is None:
@@ -72,10 +77,19 @@ def ensure_path(
     if not path.exists() and error_on_missing:
         raise FileNotFoundError
 
+    kwargs: Dict[str, Any]
+    if verify:
+        kwargs = {"backend": backend}
+    else:
+        if backend != "requests":
+            logger.warning("using requests since verify=False")
+        kwargs = {"backend": "requests", "verify": False}
+
     download(
         url=url,
         path=path,
         force=force,
+        **kwargs,
     )
     return path.as_posix()
 
@@ -89,10 +103,21 @@ def ensure_df(
     force: bool = False,
     sep: str = "\t",
     dtype=str,
+    verify: bool = True,
+    backend: Literal["requests", "urllib"] = "urllib",
     **kwargs,
 ) -> pd.DataFrame:
     """Download a file and open as a dataframe."""
-    _path = ensure_path(prefix, *parts, url=url, version=version, name=name, force=force)
+    _path = ensure_path(
+        prefix,
+        *parts,
+        url=url,
+        version=version,
+        name=name,
+        force=force,
+        verify=verify,
+        backend=backend,
+    )
     return pd.read_csv(_path, sep=sep, dtype=dtype, **kwargs)