This gives a pretty good idea of the size of these early-instar (Instar: Many invertebrates molt through dozens of progressively larger and better-developed stages as they grow. Each of these stages is known as an instar. Hard-bodied nymphs typically molt through more instars than soft-bodied larvae.) Baetid nymphs in January.
Baetidae (Blue-Winged Olives) Mayfly Nymph from the Namekagon River in Wisconsin