Squash bees pollinate the sprawling, large-leaved coyote gourd (=stinky gourd) plants so often seen in local parks.
Such specialized bees also pollinate related food crops in the cucumber family, including pumpkins, zucchini, and melons. 

With coyote squash, these native bees have little competition. Large, black carpenter bees and tiny cucumber beetles are secondary pollinators.
While I have seen the familiar imported European honeybee hover by the orange-colored blossoms, I have never witnessed one entering the flower.

Since the flowers bloom at night, that is when the squash bees are active.
Females live near the vines, alone in burrows they dig, emerging to visit the flowers in the evening.
Male bees head for the flowers in the morning, finding a place to sleep as the blooms wilt and close.
Hoping for female companions,  many perch sentry-like inside the flower, as shown here.

You may notice different structures inside the flowers. The reason is that there are male and female blossoms on the same vine.
The simpler structure is that of the male flower.

..Ron Hemberger.