seaborn のpairplotでhueの引数でエラーが出る

##書いたコード

from sklearn.datasets import load_iris
import pandas as pd
import matplotlib.pyplot as plt
import seaborn as sns
%matplotlib inline

iris=load_iris()

df=pd.DataFrame(data=iris.data, columns=["sepal length","sepal width","petal length","petal width"])

sns.pairplot(df,hue="species")

###エラー

KeyError                                  Traceback (most recent call last)
~/opt/anaconda3/lib/python3.8/site-packages/pandas/core/indexes/base.py in get_loc(self, key, method, tolerance)
   3079             try:
-> 3080                 return self._engine.get_loc(casted_key)
   3081             except KeyError as err:

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.PyObjectHashTable.get_item()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.PyObjectHashTable.get_item()

KeyError: 'species'

The above exception was the direct cause of the following exception:

KeyError                                  Traceback (most recent call last)
<ipython-input-25-8ad4f0b18072> in <module>
----> 1 sns.pairplot(df,hue="species")

~/opt/anaconda3/lib/python3.8/site-packages/seaborn/_decorators.py in inner_f(*args, **kwargs)
     44             )
     45         kwargs.update({k: arg for k, arg in zip(sig.parameters, args)})
---> 46         return f(**kwargs)
     47     return inner_f
     48 

~/opt/anaconda3/lib/python3.8/site-packages/seaborn/axisgrid.py in pairplot(data, hue, hue_order, palette, vars, x_vars, y_vars, kind, diag_kind, markers, height, aspect, corner, dropna, plot_kws, diag_kws, grid_kws, size)
   1987     # Set up the PairGrid
   1988     grid_kws.setdefault("diag_sharey", diag_kind == "hist")
-> 1989     grid = PairGrid(data, vars=vars, x_vars=x_vars, y_vars=y_vars, hue=hue,
   1990                     hue_order=hue_order, palette=palette, corner=corner,
   1991                     height=height, aspect=aspect, dropna=dropna, **grid_kws)

~/opt/anaconda3/lib/python3.8/site-packages/seaborn/_decorators.py in inner_f(*args, **kwargs)
     44             )
     45         kwargs.update({k: arg for k, arg in zip(sig.parameters, args)})
---> 46         return f(**kwargs)
     47     return inner_f
     48 

~/opt/anaconda3/lib/python3.8/site-packages/seaborn/axisgrid.py in __init__(self, data, hue, hue_order, palette, hue_kws, vars, x_vars, y_vars, corner, diag_sharey, height, aspect, layout_pad, despine, dropna, size)
   1227             # to the axes-level functions, while always handling legend creation.
   1228             # See GH2307
-> 1229             hue_names = hue_order = categorical_order(data[hue], hue_order)
   1230             if dropna:
   1231                 # Filter NA from the list of unique hue names

~/opt/anaconda3/lib/python3.8/site-packages/pandas/core/frame.py in __getitem__(self, key)
   3022             if self.columns.nlevels > 1:
   3023                 return self._getitem_multilevel(key)
-> 3024             indexer = self.columns.get_loc(key)
   3025             if is_integer(indexer):
   3026                 indexer = [indexer]

~/opt/anaconda3/lib/python3.8/site-packages/pandas/core/indexes/base.py in get_loc(self, key, method, tolerance)
   3080                 return self._engine.get_loc(casted_key)
   3081             except KeyError as err:
-> 3082                 raise KeyError(key) from err
   3083 
   3084         if tolerance is not None:

KeyError: 'species'

###試したこと
どのサイトでも皆さんはhue="species"と書いて実行してますし、feature_nameで列名を指定するのではなく、実際に直接列名を指定してもみました。
なぜ"species"でエラーが出るのでしょうか？