Complex sentence: Females will fly 1--3 km before laying their eggs on the river which then sink to the bottom and hatch after about 45 days, the larvae then develop in the mud for as long as three years before hatching.
Split into simpler sentences: Females will fly 1--3 km before laying their eggs on the river, which then sink to the bottom and hatch after about 45 days. The larvae develop in the mud for as long as three years before hatching.